Eccentric Training for Tendinopathies in Athletes: A Scoping Review and Evidence Gap Map

Abstract

Tendinopathies are prevalent in athletic populations, particularly in sports requiring repetitive high-load activities. Eccentric training is widely recommended for rehabilitation, yet variability in protocols and inconsistent methodological reporting limit standardization. This scoping review aimed to map existing evidence on eccentric training for tendinopathies in athletes, characterize intervention parameters, evaluate clinical outcomes and safety, and identify methodological gaps to inform future practice and research. Searches of PubMed, Scopus, and Web of Science were conducted. Eligible studies included athletes with tendinopathy undergoing eccentric training interventions. Randomized and non-randomized controlled trials were considered. Data extraction included intervention design, tendon site, loading parameters, outcomes, and adverse events. Critical appraisal was performed using RoB 2 and ROBINS-I tools. Thirty-one studies were included. Most examined patellar tendinopathy in volleyball and basketball players or Achilles tendinopathy in runners and soccer athletes. Protocols varied substantially in load, frequency, and progression strategies. Pain monitoring was integral, often allowing exercise into moderate discomfort. Eccentric training consistently improved pain and function, with heavy slow resistance and adjunct modalities showing comparable or additive effects. Return-to-sport rates were high, and adverse events were minimal. However, performance outcomes, tendon structure, and safety reporting were inconsistently assessed. Eccentric training consistently reduces pain and improves function in athletes with tendinopathy. Evidence is less consistent regarding performance outcomes, tendon remodeling, and comparative superiority over alternative interventions. Standardized reporting of protocols, safety, and sport-specific adaptations is needed to strengthen recommendations for athletic rehabilitation.

Key points.

• Across 31 studies, eccentric training was the most frequently investigated conservative approach for athletic tendinopathies, applied across multiple tendon sites (patellar, Achilles, proximal hamstring) and sports, most often volleyball, soccer, and running.

• Evidence supports eccentric training as generally safe and effective for improving pain and function, while findings on performance, tendon structure, and return-to-sport remain inconsistent and underexplored.

• Evidence gaps include small sample sizes, limited sport-specific outcomes, scarce long-term follow-up, and insufficient safety reporting, informing priorities for future athlete-centered research.

Introduction

Tendinopathies are chronic tendon disorders characterized by pain, swelling, and impaired function, typically resulting from repetitive mechanical loading (Millar et al., 2021). Unlike acute tendon injuries, these conditions involve degenerative changes in the tendon matrix, including collagen disorganization, increased ground substance, and neovascularization, rather than classic inflammatory responses (Sandrey, 2003). Tendinopathies are highly prevalent in athletic populations; they account for approximately 30-50% of overuse injuries in sports (Florit et al., 2019), affecting both recreational and elite athletes. The Achilles tendon, patellar tendon, rotator cuff tendons, and lateral elbow extensor tendons are most commonly involved (Maffulli et al., 2003), reflecting the repetitive high-load demands of running, jumping, throwing, and racquet sports. For example, Achilles tendinopathy is reported in 8-15% of runners (Munteanu and Barton, 2011), while patellar tendinopathy may affect up to 40% of volleyball players (Lian et al., 2003).

The pathophysiology of tendinopathy is multifactorial (Millar et al., 2021). Mechanical overload - both in magnitude and frequency - is a key trigger for degenerative changes (Magnusson et al., 2010). Central mechanisms include failed healing responses, collagen disorganization, neovascularization, and altered tendon metabolism (Fouda et al., 2017). Neuromuscular and biomechanical factors, such as muscle-tendon imbalances, decreased flexibility, and abnormal load distribution, also contribute to the development and persistence of tendon disorders (Mersmann et al., 2017). The interplay between mechanical stress and cellular response is mediated by mechanotransduction, where tendon cells convert mechanical loading into biochemical signals, promoting collagen synthesis and tendon remodeling (Stańczak, 2024).

Conservative management aims to reduce pain, restore tendon function, and prevent recurrence (Cardoso et al., 2019). Modalities include activity modification, soft tissue therapy, pharmacologic interventions, shockwave therapy, and progressive loading programs (Cardoso et al., 2019). Among these, eccentric exercise (ECC) has gained prominence due to its physiological basis and evidence of clinical efficacy (Camargo et al., 2014; O’Neill et al., 2015). Eccentric exercise involves controlled lengthening of a muscle-tendon unit under load, as opposed to concentric contractions where the muscle shortens (Couppé et al., 2015). It generates higher tendon tension with lower metabolic cost, making it particularly effective for stimulating tendon remodeling while minimizing fatigue (Camargo et al., 2014). Eccentric loading may enhance collagen synthesis, tendon matrix organization, and upregulation of growth factors like IGF-I, facilitating tendon healing (KJaer, 2004).

Protocols such as those described by Alfredson et al. (Alfredson et al., 1998) for Achilles tendinopathy have demonstrated safety and effectiveness, typically involving repeated sets of slow, controlled eccentric contractions, while load and volume are adjusted based on the athlete’s pain response rather than maximal strength testing. Curwin’s method (Curwin and Stanish, 1984) similarly emphasizes pain-guided progression, combining concentric and eccentric movements while performing the eccentric phase at a faster rate, targeting 20-30 repetitions per set with 3 sets of 10 repetitions and adjusting load or speed to maintain a moderate level of discomfort consistent with functional activity. Specific tendon-targeted exercises have been described to optimize loading: for the Achilles, athletes progress from flat-ground calf raises to leaning calf raises and stair-based exercises, incorporating supine calf raises on a leg press machine to modulate load, and anterior step-downs to engage the soleus as a decelerator of tibial motion during dorsiflexion (Lorenz, 2010); for the patellar tendon, leg press, decline squats, and eccentric step-downs are employed, ensuring concentric movements are performed with both legs and the eccentric phase solely with the involved tendon (Lorenz, 2010); for lateral epicondylitis, eccentric wrist extension, eccentric radial deviation, and eccentric supination exercises are performed with passive return to the start position, with progression achieved by increasing lever arm or external load (Lorenz, 2010). Evidence suggests that these interventions are effective in reducing pain, improving function, and supporting return to sport, yet most studies emphasize clinical outcomes rather than detailed methodological reporting, including load prescription, exercise progression, and sport-specific adaptation (Habets and van Cingel, 2015; Chen and Baker, 2021).

Although eccentric exercise is widely used, no scoping review has synthesized both the clinical and methodological aspects of eccentric training interventions in athletes. Athletes have unique performance demands, and tendon loading must be carefully adjusted. Mapping existing evidence can highlight methodological gaps, such as variability in sets, repetitions, load progression, pain monitoring, and reporting of functional outcomes, ultimately guiding standardized, evidence-based protocols for athletic populations. Therefore, a scoping review is warranted to systematically map the existing literature on eccentric training for tendinopathies in athletes, describe the parameters and progression strategies of interventions, and identify gaps in methodological reporting, ultimately informing standardized, evidence-based protocols for athletes. In this way, this scoping review aims to: (i) map existing studies on eccentric training for tendinopathies in athletes; (ii) characterize intervention protocols (load, frequency, volume, progression, pain monitoring); (iii) summarize clinical outcomes and efficacy; (iv) identify harms or adverse effects; and (v) identify methodological gaps and inform recommendations for future research and practice in sports-specific populations.

Methods

Protocol and registration

The protocol for this scoping review was prepared following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. A pre-defined protocol was registered on the Open Science Framework (OSF) platform on August 21, 2025. The registration can be publicly accessed at the following URL: osf.io/q4vy3.

Eligibility criteria

The selection of studies for inclusion in the review was guided by a set of well-defined eligibility criteria based on the Population-Concept-Context (PCC) framework, a standard approach for scoping reviews. No restrictions on language or publication years were applied.

Inclusion Criteria

Population: Studies on human participants who are diagnosed with tendinopathy and are identified as athletes (Tier 2 or more in Participants Classification Framework) (McKay et al., 2022). This includes individuals who exercise to improve performance or who participate in organized sports. The definition was broad to include different levels of athleticism based on training volume and competition level, such as competitive athletes and recreational athletes.

Concept: Studies that investigate any form of eccentric training for tendinopathy, regardless of the specific protocol (e.g., heavy slow resistance).

Context: Studies that investigate eccentric training for tendinopathies within the context of athletic training, sports rehabilitation, or recovery protocols. Considered study designs included randomized experimental and controlled studies and non-randomized experimental and controlled studies.

Exclusion Criteria

Population: Studies on non-human subjects or on individuals who do not have a diagnosis of tendinopathy or who do not meet the definition of an athlete. This includes those classified as "exercisers" or "physically active practitioners," who primarily engage in physical activity for general health and fitness, typically with a training volume of less than 2.5 hours per week. Studies that focus on individuals with specific physical impairments classified as Paralympic athletes will also be excluded, as their classification system is distinct.

Concept: Studies that do not investigate eccentric training as an intervention for tendinopathy.

Context: Studies that do not investigate eccentric training within the context of athletic training, sports rehabilitation, or recovery protocols. Review articles, case reports, and studies without accessible full texts were excluded, as they do not offer the primary, unbiased data required for systematic analysis.

Information sources

A search was conducted across multiple electronic databases on August 21, 2025. The databases selected for this review - PubMed, Scopus, and Web of Science - were chosen for their strong relevance to the fields of biomedicine, physical therapy, and allied health. The search covered all records available from each database's inception up to the search date. To enhance the thoroughness of the review, additional literature was located through a supplementary search on Google Scholar, aimed at capturing both peer-reviewed and gray literature; this step was finalized on August 21, 2025. Additionally, a manual review of reference lists from all included studies and related systematic reviews was carried out to identify any further eligible articles not retrieved through database searches. This manual screening was also completed on August 21, 2025.

Searches

The search strategy was carefully developed to ensure specificity by combining keywords with controlled vocabulary terms. Customized search strings were created for each database, taking into account the unique syntax and indexing systems of each platform. The search was organized around three main concepts: the target population (athletes), the intervention (eccentric training), and the condition (tendinopathy). This method was designed to capture all relevant studies, regardless of the specific terminology used by the authors.

A broad range of terms and their variants was included to maximize retrieval. Boolean operators (AND/OR) were employed to combine these terms logically, increasing the precision and relevance of the search results.

The finalized search strategy, along with the selected databases and specific terms used, is detailed in Table 1.

Table 1.

Search strategy.

Participants		Intervention		Condition
Athlete* OR player* OR sportspeople OR sportman OR sportwoman OR sportmen OR sportwomen OR sport* OR competitor*	AND	Eccentric* OR “resistance training” OR “strength training” OR exercise	AND	Tendinopathy OR tendinosis OR tendonitis OR epicondylosis OR epicondylitis OR “tennis elbow”

Selection of sources of evidence

The selection of sources of evidence followed a two-stage process. The initial search results were de-duplicated and imported into a review management software (Endnote online). Two independent authors (R.T. and G.O.) then screened the titles and abstracts of all identified records against the established eligibility criteria. At this stage, studies were categorized as "include," "exclude," or "unclear." Any record flagged as "unclear" or "include" by at least one author proceeded to the next stage. In the second stage, the full texts of all selected records were retrieved and assessed for final inclusion by the same two authors. Any discrepancies between the authors' decisions were resolved through a formal consensus meeting, with a third author (K.G.) serving as an arbiter if a consensus could not be reached. This systematic, multi-stage process was designed to minimize the risk of author bias and ensure the final selection of studies was both comprehensive and objective.

Data charting process

Following the study selection process, data were extracted from each included article using a pre-defined data charting form. This form was developed collaboratively by the author’s team and was piloted on a subset of studies (n = 5) to ensure consistency and accuracy before its use. The extraction process was standardized and systematic, ensuring that data collection was consistent regardless of which author was charting the data. The variables extracted from each study included the study design, participant characteristics, type and location of tendinopathy, specifics of the intervention (e.g., protocol, duration, and frequency), outcome measures used, and key findings reported.

Data items

In accordance with the objectives of this review, data were extracted across several domains.

Intervention-related variables included the type of eccentric exercise (e.g., decline squat, slow heavy resistance), targeted tendon, load prescription (absolute or relative, such as % of body weight or repetition maximum), frequency (sessions per week), volume (sets, repetitions), duration of intervention (weeks), and overall program length. Progression strategies were charted (e.g., weekly load increments, speed variation, range of motion adjustments, or pain-guided progression criteria). Where reported, pain monitoring strategies were recorded (e.g., allowance of up to 5/10 pain on a numerical rating scale [NRS] during exercise, visual analogue scale [VAS] criteria for progression or modification).

Efficacy outcomes were summarized, including: (i) Pain (e.g., VAS, NRS, or tendon-specific pain scores during activity or at rest); (ii) Function (e.g., Victorian Institute of Sport Assessment [VISA-A, VISA-P, VISA-H], Lower Extremity Functional Scale, Disabilities of the Arm, Shoulder and Hand [DASH]); (iii) Performance and return to sport (e.g., time to return to training or competition, sport-specific performance tests such as hop test, jump height, or strength testing); and (iv) Tendon structure and physiology (where assessed, e.g., ultrasound imaging measures of tendon thickness, Doppler activity, MRI findings, or stiffness using elastography).

Safety outcomes were extracted wherever reported, including: (i) Adverse events (e.g., exacerbation of symptoms, increase in pain beyond baseline, development of compensatory injuries); (ii) Withdrawal or discontinuation of intervention due to pain or intolerance; (iii) Incidence of serious adverse effects (e.g., tendon rupture or significant musculoskeletal injury during intervention).

Methodological and reporting variables included intervention fidelity (e.g., whether supervised or unsupervised), adherence (e.g., reported completion rates of sessions), co-interventions (e.g., adjunct therapies such as shockwave, injections, or stretching), and level of detail in reporting according to exercise intervention.

Critical appraisal of individual sources of evidence

Although critical appraisal is not mandatory in scoping reviews, it was undertaken in this study to provide greater insight into the methodological quality of the available evidence and to contextualize the strength and limitations of reported findings. Given the diversity of study designs eligible for inclusion (randomized and non-randomized experimental and controlled studies), design-specific risk of bias tools was applied.

Randomized controlled trials (RCTs) were assessed using the Cochrane Risk of Bias 2 (RoB 2) tool (Flemyng et al., 2023). This instrument evaluates risk of bias across five domains: (i) bias arising from the randomization process; (ii) bias due to deviations from intended interventions; (iii) bias due to missing outcome data; (iv) bias in measurement of the outcome; and (v) bias in selection of the reported result. Each domain is rated as low risk, some concerns, or high risk of bias, based on a structured series of signaling questions. These domain-level judgments are then synthesized into an overall risk of bias judgment for each outcome.

Non-randomized intervention studies were assessed using the Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) tool (Sterne et al., 2016). This instrument evaluates seven domains of bias: (i) bias due to confounding; (ii) bias in selection of participants; (iii) bias in classification of interventions; (iv) bias due to deviations from intended interventions; (v) bias due to missing data; (vi) bias in measurement of outcomes; and (vii) bias in selection of the reported result. Each domain is judged on a scale from low risk, moderate risk, serious risk, critical risk of bias, or no information. As with RoB 2, signaling questions guide the assessment, and judgments across domains are combined to provide an overall risk of bias rating for each study.

Appraisal findings were charted alongside study data to identify trends in methodological quality (e.g., inadequate reporting of progression strategies, limited monitoring of adverse effects, lack of blinding in outcome measurement) and guided the formulation of recommendations for future research.

Synthesis of results

The charted data were synthesized using both descriptive and visual approaches to provide an overview of eccentric training interventions for tendinopathy in athletes. Study characteristics (e.g., design, population, tendon involved, and context) and intervention features (e.g., load, frequency, volume, progression, pain monitoring) were summarized using frequency counts, and narrative description. Clinical and safety outcomes were grouped into domains (pain, function, performance/return-to-sport, tendon structure/physiology, and adverse events) and summarized to highlight patterns of evidence across different study designs and athletic populations. The results of the critical appraisal were integrated descriptively to contextualize the methodological rigor of included studies and to identify recurrent areas of bias, incomplete reporting, or heterogeneity in outcome measures.

In addition to narrative and tabular synthesis, an evidence gap map was developed to visually display the distribution of evidence across key dimensions, including study design, athlete population (e.g., sport, competition level), tendon site, intervention parameters (e.g., type of eccentric exercise, progression strategy), and outcome domains (pain, function, performance, tendon structure, safety). Data visualization was employed to enhance interpretability and highlight areas of strength and paucity in the evidence base.

Results

Selection of sources of evidence

The study selection process for this systematic review followed the PRISMA flowchart (Figure 1). Initially, a total of 2812 records were identified through database searches across PubMed (n = 564), Web of Science (n = 858), and Scopus (n = 1390). After removing duplicate records (n = 947), 1865 records remained for screening.

Figure 1.

PRISMA flowchart (Page et al., 2021).

Following the screening process, 1801 records were excluded based on title and abstract review. A total of 64 reports were sought for retrieval. All 64 reports were successfully retrieved and assessed for eligibility. Of these, 33 reports were excluded due to the following reasons: 15 based on population criteria (e.g., no tendinopathy, no athletes), 4 based on concept relevance (e.g., no eccentric training), and 14 based on context criteria (e.g., no control groups, retrospective studies). Ultimately, 31 studies were included in the final scoping review.

Characteristics of sources of evidence

Across the included studies focusing on Pattelar tendon (Table 2), Achilles tendon (Table 3), and hamstring tendon (Table 4), the majority of trials focused on participants in their late teens to early thirties, particularly competitive athletes in jumping sports (Visnes et al., 2005; Bahr et al., 2006; Breda et al., 2021). A smaller subset of interventions recruited middle-aged recreational exercisers with chronic symptoms, often with Achilles involvement (Beyer et al., 2015; Habets et al., 2021; Demir Benli et al., 2022). In terms of sex distribution, most studies enrolled predominantly or exclusively male athletes, especially in soccer and volleyball cohorts (Visnes et al., 2005; Langberg et al., 2007; Niering and Muehlbauer, 2023), though some reported a balanced or mixed representation (Stergioulas et al., 2008; Cunha et al., 2012; Demir Benli et al., 2022).

Table 2.

Characteristics of the included studies focusing on Pattelar tendon.

Study	Design	Randomized	Controlled	Number of Groups	Sample Size (N per Group)	Participants	Sport Type (s)	Age Range / Mean	Sex	Tendon Involved	Outcomes Collected	Follow-up Duration
(Abat et al., 2016)	Randomized Controlled Trial (RCT, parallel groups)	Yes	Yes	2 (Electro-physiotherapy + eccentric; USGET + eccentric)	G1: 32; G2: 32 (60 completed)	Athletes with unilateral insertional patellar tendinopathy	Athletically active (not sport-specific)	20–60 yrs (mean ~31)	G1: 24M/8F; G2: 27M/5F	Patellar tendon (inferior pole)	VISA-P, USG (thickening, hypoechoic areas, calcifications, vascularization)	2 months (or until VISA-P ≥ 90), biweekly
(Bahr et al., 2006)	RCT (parallel groups + secondary surgical arm)	Yes	Yes	2 (Eccentric training; Surgery); Secondary: Surgery after failed training	G1: 15 knees; G2: 16 knees; Secondary: 9 knees	Athletes/active adults with patellar tendinopathy (Blazina grade IIIB)	Various	≥18 yrs (mean ~25–30)	Mixed	Patellar tendon (proximal)	VISA, VAS pain, satisfaction, 1RM leg press, CMJ	3, 6, 12 months
(Biernat et al., 2014)	RCT (rehabilitation during season)	Yes	Yes	2 (Eccentric squat + functional training; Control, volleyball only)	G1: 15; G2: 13	Male youth volleyball players	Volleyball	16–19 yrs (mean 17.7 E; 16.5 C)	All male	Patellar tendon (jumper’s knee)	VISA-P, USG + Doppler, isokinetic strength, CMJ	24 wks (baseline, 12, 24)
(Breda et al., 2021)	RCT (stratified, investigator-blinded; JUMPER trial)	Yes	Yes	2 (PTLE; EET [control])	G1: 38; G2: 38 (76 total)	Athletes with patellar tendinopathy	Basketball, volleyball, others	18–35 yrs (mean: 24 ± 3.5 PTLE; 24 ± 4.2 EET)	PTLE: 82%M; EET: 71%M	Patellar tendon (inferior pole)	VISA-P (primary), return to sport, satisfaction, adherence, USG, VAS	12 and 24 wks
(Cannell et al., 2001)	RCT	Yes	Yes	2 (Drop squats [ecc]; Leg extension/curl [conc])	G1: 10; G2: 9	Athletes with jumper’s knee	Basketball, soccer, running, volleyball, tennis, squash, rowing, football, gymnastics	15–50 yrs (mean 26)	13M/6F	Patellar tendon (inferior pole)	VAS pain, return to sport, isokinetic strength, thigh girth	12 wks
(Cunha et al., 2012)	RCT (prospective)	Yes	Yes	2 (Pain group [ecc with max pain]; No-pain group)	G1: 10; G2: 7	Athletes with PT (US/MRI confirmed)	Track & field, basketball, capoeira, soccer, handball, combat sports, triathlon, volleyball	PG: 24.1 ± 8.3; WP: 26 ± 5.9	14M/3F	Patellar tendon	VISA-P, VAS	12 wks
(Frohm et al., 2007)	RCT (prospective clinical trial)	Yes	Yes	2 (Eccentric overload in Bromsman device; Standard decline squat)	G1: 11; G2: 9	Athletes with PT (≥3 mo continuous or ≥6 mo recurrent; US/MRI confirmed)	Competitive (17), recreational (3)	G1: 26 ± 8 yrs; G2: 28 ± 8 yrs	16M/4F	Patellar tendon	VISA-P, VAS, isokinetic strength, CMJ, one-leg triple hop	12 wks
(Jonsson and Alfredson, 2005)	RCT (prospective)	Yes	Yes	2 (Quadriceps eccentric; Quadriceps concentric)	ET: 10 tendons; CT: 9 tendons	Athletes with chronic PT (≥8 mo)	Running, soccer, basketball, handball, floorball	ET: 25.7 ± 9.9; CT: 24.1 ± 6.4	ET: 7M/1F; CT: 6M/1F	Patellar tendon (proximal)	VAS (pain), VISA, satisfaction	12 wks; 32.6 mo FU
(Kongsgaard et al., 2009)	Single-blind RCT	Yes	Yes	3 (Corticosteroid inj.; Eccentric; HSR)	39 (13 per group)	Recreational male athletes with PT	Running, soccer, ball sports	32 ± 9 yrs	67%M	Patellar tendon	VISA-P, VAS, FAOS, Microcirculation	12 wks + 6 mo FU
(Knež and Hudetz, 2023)	Multicenter single-blind RCT	Yes	Yes	2 (17° decline board; 25° decline board)	70 total (35 per group)	Adults with chronic PT (>3 mo)	Soccer, basketball, running	25.0 ± 6.8 (17°); 24.1 ± 7.0 (25°)	74.3%M (17°); 65.7%M (25°)	Patellar tendon (midportion)	VAS, VISA-P, KOOS, Lysholm/Tegner	12 wks
(Lee et al., 2020)	RCT	Yes	Yes	2 (Exercise; Exercise+ESWT)	Ex: 14; Comb: 16	Competitive athletes with PT (≥3 mo, US-confirmed)	Volleyball, basketball, handball	21–24 yrs	Mixed	Patellar tendon	VISA-P, VAS, tendon strain/stiffness, EMG	12 wks
(Niering and Muehlbauer, 2023)	Longitudinal RCT	Yes	Yes	2 (CON; ALT)	CON: 18; ALT: 16	Elite youth soccer players with PT	Soccer	CON: 15.1 ± 0.8; ALT: 15.4 ± 1.0	100%M	Patellar tendon (proximal)	VAS, DJ, JaR, CODS, Speed, Endurance, AMS	20 wks
(Ruffino et al., 2021)	RCT	Yes	Yes	2 (Inertial flywheel; HSR)	20; 21	Adults with PT	Volleyball, basketball, soccer, running	IF: 27.5 ± 5.4; HSR: 31.7 ± 8.7	IF: 0F; HSR: 1F	Patellar tendon	VISA-P, PSFS, EQ-5D, US imaging, load test	12 wks
(Sánchez-Gómez et al., 2022)	Double-blind RCT	Yes	Yes	2 (HMB vs Placebo)	4; 4	Federated athletes with PT	Basketball, volleyball, handball, athletics	18–49 yrs	Mixed (2M/2F per group)	Patellar tendon	VISA-P, VAS, CMJ, power, 5RM	4 wks + 4 wks FU
(Gómez et al., 2023)	Longitudinal (rehab)	No	Yes	1 (Combined intervention: ECC + stretching + ESWT + manual therapy)	8 (6M/2F)	Federated athletes with PT	Basketball, volleyball, handball, jumping	18–49 yrs (mean 27.1 ± 8.3)	6M/2F	Patellar tendon	VISA-P, VAS, CMJ, Back Squat, 5RM	8 wks
(van Ark et al., 2016)	RCT	Yes	Yes	2 (Isometric; Isotonic)	13; 16	Volleyball/ basketball players with PT	Volleyball, basketball	16–32 yrs	Mixed	Patellar tendon	NRS pain (SLDS), VISA-P, global rating, adherence	4 wks
(Visnes et al., 2005)	RCT (2-group repeated measures)	Yes	Yes	2 (Eccentric; Control)	13; 16	Elite & 1st division volleyball players with PT	Volleyball	19–35 yrs (mean 26.6)	Mixed (5F each group)	Patellar tendon (majority); some quadriceps	VISA, global eval, jump tests	12 wks + 6 mo FU
(Young et al., 2005)	RCT (parallel, repeated measures)	Yes	Yes	2 (Decline squat; Step squat)	17 total	Elite volleyball players (Victorian State League) with PT	Volleyball	27.3 ± 1.8 yrs	13M/4F	Patellar tendon (proximal)	VISA, VAS	12 wks; 12 mo FU

CT = Concentric Training; CON = Control group; CMJ = Countermovement Jump; DJ = Drop Jump; ESWT = Extracorporeal Shockwave Therapy; ECC = Eccentric Exercise / Eccentric Training; EET = Eccentric Exercise Therapy; ET = Eccentric Training group (sometimes “Eccentric Quadriceps Training”); HSR = Heavy Slow Resistanc; RCT = Randomized Controlled Trial; FAOS = Foot and Ankle Outcome Score; F = Female; M = Male; NRS = Numeric Rating Scale (pain); VAS = Visual Analog Scale (pain); VISA-P = Victorian Institute of Sport Assessment – Patellar; SLDS = Single Leg Decline Squat; KOOS = Knee Injury and Osteoarthritis Outcome Score; PT = Patellar Tendinopathy

Table 3.

Characteristics of the included studies focusing on Achilles tendon.

Study	Design	Randomized	Controlled	Number of Groups	Sample Size (N per Group)	Participants	Sport Type (s)	Age Range / Mean	Sex	Tendon Involved	Outcomes Collected	Follow-up Duration
(Alfredson et al., 1998)	Controlled Clinical Trial (surgical comparator)	No	Yes	2 (Eccentric training; Surgery)	G1: 15; G2: 15	Recreational athletes with chronic Achilles tendinosis	Jogging, soccer	Training: 44.3 ± 7.0 yrs; Surgery: 39.6 ± 7.9 yrs	Training: 12M/3F; Surgery: 11M/4F	Achilles tendon (midportion)	VAS pain, isokinetic calf strength, USG	Training: 12 wks; Surgery: 24 wks postop
(Demir Benli et al., 2022)	RCT (parallel groups)	Yes	Yes	2 (Eccentric exercise; ESWT)	G1: 30; G2: 30	Adults with chronic midportion Achilles tendinopathy	Fitness, soccer, volleyball, pilates, walking	18–55 yrs (mean 37.3 ± 12.2)	40F/23M	Achilles tendon (midportion)	VAS pain, VISA-A, USG, tendon strain	12 wks treatment, 2 yrs follow-up
(Beyer et al., 2015)	RCT (parallel groups)	Yes	Yes	2 (Eccentric exercise; HSR)	G1: 25; G2: 22	Recreational athletes with midportion Achilles tendinopathy	Fitness, volleyball, badminton	31–60 yrs (mean 48 ± 2)	ECC: 18M/7F; HSR: 14M/8F	Achilles tendon (midportion)	VISA-A, VAS, Doppler US, activity level	12 wks treatment, 52 wks follow-up
(Habets et al., 2021)	Multicenter single-blind RCT	Yes	Yes	2 (Alfredson eccentric; Silbernagel conc-eccentric)	AG: 18; SG: 22	Recreational athletes with chronic midportion AT	Walking, running, ball sports	AG: 44.7 ± 9 yrs; SG: 49.9 ± 10 yrs	AG: 8F/10M; SG: 10F/12M	Achilles tendon (midportion)	VISA-A, VAS, EQ-5D, Global Perceived Effect	12, 26, 52 wks
(Knobloch et al., 2007)	RCT	Yes	Yes	3 (AirHeel+ eccentric; Eccentric only; Symptomatic eccentric)	112 total (54, 64, 62)	Adults with unilateral AT	Running, soccer, others	48 ± 12 yrs	59–61%M	Achilles tendon (midportion /insertional)	VAS, FAOS	12 wks
(Knobloch et al., 2008)	RCT	Yes	Yes	2 (Eccentric+ AirHeel; Eccentric only)	116 (57, 59)	Adults with unilateral AT	Running, soccer, others	47–48 ± 11 yrs	63–67%M	Achilles tendon (main body)	VAS, FAOS, Microcirculation	12 wks
(Langberg et al., 2007)	RCT (prospective)	Yes	Yes	2 (Injured vs. healthy)	6	Elite male soccer players with unilateral AT	Soccer	Injured: 26 ± 1; Healthy: 22 ± 1	100%M	Achilles tendon (main body)	VAS, collagen turnover (PICP, ICTP), microdialysis	12 wks
(Malliaras et al., 2013)	RCT (4-group)	Yes	Yes	4 (Control; Concentric; Standard ECC; High-load ECC)	38 total (~9–10 per group)	Healthy males, 18–35 yrs	Soccer, track & field, racquet	26–29 yrs	All male	Achilles tendon	5RM, torque, stiffness, modulus, CSA, stress	12 wks
(Radovanović et al., 2022)	Controlled clinical trial	Yes	Yes	3 (Passive therapy; Alfredson; High-load)	14; 15; 15	Males with chronic AT	Soccer, volleyball	24 ± 8 yrs	100%M	Achilles tendon	VISA-A, NRS pain, stiffness, Young’s modulus, jump height	12 wks; 6 mo FU
(Rompe et al., 2007)	RCT (primary care)	Yes	Yes	3 (Eccentric; SWT; Wait-and-see)	25 each	Adults with chronic non-insertional AT	Various	48 ± 9 yrs	64%F	Achilles tendon	VISA-A, NRS pain, tenderness, US size	12 wks; 4 mo FU
(Rompe et al., 2009)	RCT (primary care)	Yes	Yes	2 (ECC; ECC+SWT)	34 each	Adults with midportion AT	Various	G1: 46.2 ± 10.2; G2: 53.1 ± 9.6	~59%F	Achilles tendon	VISA-A, NRS pain, tenderness, US size	12 wks; 4 mo FU
(Stergioulas et al., 2008)	RCT	Yes	Yes	2 (Laser; Placebo laser)	13; 13	Adults with chronic AT	Basketball, volleyball, various	Laser: 30.1 ± 4.8; Placebo: 28.8 ± 4.8	Mixed	Achilles tendon	VAS pain, stiffness, crepitation, tenderness, dorsiflexion	8 wks; 12 wks FU

AG = Alfredson Group (isolated eccentric protocol); ALT = Alternative Training Group; AMS = Achievement Motivation Scale (psychological); AT = Achilles Tendinopathy; CMJ = Countermovement Jump; CODS = Change of Direction Speed; CON = Control group; CSA = Cross-Sectional Area; CT = Concentric Training; DJ = Drop Jump; ECC = Eccentric Exercise / Eccentric Training; EET = Eccentric Exercise Therapy; EMG = Electromyography; EQ-5D = EuroQol 5 Dimensions (Quality of Life); ESWT = Extracorporeal Shockwave Therapy; ET = Eccentric Training group (sometimes “Eccentric Quadriceps Training”); FAOS = Foot and Ankle Outcome Score; F = Female; FU = Follow-up; HMB = β-Hydroxy β-Methylbutyrate (supplement); HSR = Heavy Slow Resistance; KOOS = Knee Injury and Osteoarthritis Outcome Score; M = Male; MRI = Magnetic Resonance Imaging; NRS = Numeric Rating Scale (pain); NPRS = Numeric Pain Rating Scale; PHT = Proximal Hamstring Tendinopathy; PICP = Procollagen type I C-peptide (collagen synthesis marker); PSFS = Patient Specific Functional Scale;; PTLE = Progressive Tendon-Loading Exercise; RCT = Randomized Controlled Trial; SG = Silbernagel Group (concentric–eccentric protocol); SLDS = Single Leg Decline Squat; SWT = Shockwave Therapy; US = Ultrasound; USG = Ultrasonography; VAS = Visual Analog Scale (pain); VISA-A = Victorian Institute of Sport Assessment – Achilles; 1RM / 5RM = One / Five Repetition Maximum (strength test); YYIRL1 = Yo-Yo Intermittent Recovery Level 1 Test.

Table 4.

Characteristics of the included studies focusing on hamstring tendon.

Study	Design	Randomized	Controlled	Number of Groups	Sample Size (N per Group)	Participants	Sport Type (s)	Age Range / Mean	Sex	Tendon Involved	Outcomes Collected	Follow-up Duration
(Verma et al., 2022)	RCT (2-arm pretest–posttest)	Yes	Yes	2 (Experimental HPLT; Conventional PT)	18; 18	National-level track & field athletes with PHT	Track & field	18–35 yrs (mean ~22.5)	Mixed	Proximal hamstring tendon	NPRS pain, Isokinetic Peak Torque	3 wks

HPLT = High Power Laser Therapy; PT: personal training; NPRS = Numeric Pain Rating Scale

Regarding the sports represented, the most common discipline was volleyball, featured prominently in studies on patellar tendinopathy (Young et al., 2005; Visnes et al., 2005; Biernat et al., 2014; van Ark et al., 2016; Lee et al., 2020), followed by soccer, particularly in Achilles-related trials (Langberg et al., 2007; Malliaras et al., 2013; Niering and Muehlbauer, 2023). Basketball and track & field also appeared frequently as representative jumping or running sports (Cannell et al., 2001; Cunha et al., 2012; Ruffino et al., 2021). With respect to the tendon involved, patellar tendinopathy was the most commonly studied condition in competitive athletes (Bahr et al., 2006; Breda et al., 2021; Ruffino et al., 2021), while Achilles midportion tendinopathy dominated in mixed or recreational cohorts (Alfredson et al., 1998; Rompe et al., 2007; Beyer et al., 2015; Habets et al., 2021). A few studies extended the scope to other regions such as the proximal hamstring tendon (Verma et al., 2022) or quadriceps tendon (Visnes et al., 2005).

The eccentric training protocols (Table 5) described across the studies showed considerable heterogeneity. Bodyweight decline squats performed on a 25° board were the most common exercise strategy for patellar tendinopathy (Young et al., 2005; Visnes et al., 2005; Jonsson and Alfredson, 2005; Bahr et al., 2006; Breda et al., 2021). For Achilles tendinopathy, the Alfredson heel-drop program - consisting of eccentric calf raises with the gastrocnemius and soleus (straight and bent-knee variations) - was the most widely used (Alfredson et al., 1998; Knobloch et al., 2007; 2008; Rompe et al., 2007; 2009; Habets et al., 2021). These core protocols were often modified with additional resistance (typically backpack weights with incremental loading of 5-10 kg) or adapted with alternative devices, such as barbell-guided squats (Frohm et al., 2007), inertial flywheels (Ruffino et al., 2021), or adjunctive modalities like AirHeel wraps (Knobloch et al., 2007; 2008). In some studies, eccentric protocols were paired with comparators such as shockwave therapy (Rompe et al., 2007, 2009; Demir Benli et al., 2022), laser therapy (Stergioulas et al., 2008), or high-load slow resistance (Beyer et al., 2015; Ruffino et al., 2021).

Table 5.

Characteristics of the eccentric training.

Study	Eccentric Training Protocol	Load	Frequency	Volume	Progression Strategy	Pain Monitoring	Comparator Group	Comparator Details	Adverse Events/Harms
Pattelar tendon
(Abat et al., 2016)	Incline eccentric squats (25° decline), single-leg	Bodyweight only	3×/week	3×15 reps	Fixed (no structured progression; until VISA-P ≥ 90)	VISA-P	Yes	Group 1: Electro-physiotherapy (US, Laser CO2, IFC, 3×/week × 8w); Group 2: USGET (every 2w, 3 punctures, US-guided)	None reported
(Bahr et al., 2006)	Decline-board eccentric squats (25°), single-leg eccentric	Bodyweight → backpack (5-kg increments)	2×/day	3×15 reps per session	Load adjusted to maintain pain 4–5/10	VISA, VAS	Yes	Group 2: Open surgical debridement + postop rehab; Secondary surgery if training failed	None reported
(Biernat et al., 2014)	Decline-board squats (25°), added unstable surface + functional training	Bodyweight	Daily (except match/training days)	3×15 reps (per leg)	Progression by unstable surface/ functional additions	VAS (stop if >4/10)	Yes	Control: Volleyball training only	None reported
(Breda et al., 2021)	Pain-provoking EET, single-leg decline squat (25° board)	Bodyweight → backpack weights	2×/day	3×15 reps	Increase load with backpack if pain ≤3/10	Pain ≥5/10 during exercise; ≤3/10 to progress	Yes	PTLE (progressive tendon- loading: isometric → isotonic → plyometric → sport-specific)	None reported
(Cannell et al., 2001)	Drop squats, rapid knee unlocking	Bodyweight → hand weights (2–18 kg)	5×/week	3×20 reps	Gradual increase in weights; return-to-run progression	Pain expected; icing post-exercise	Yes	Leg extension/curl (concentric, progressive 4.5–32 kg, 5×/week)	None reported
(Cunha et al., 2012)	Decline squat (25°), single-leg eccentric	Squat bar + plates (5 kg increments)	3×/week	3×15 reps	PG: max tolerated pain; WP: pain-free	PG: “max pain possible”; WP: no pain	Yes	WP: same protocol without pain allowed	None reported
(Frohm et al., 2007)	Bromsman device (eccentric overload)	Up to 320 kg barbell (machine)	2×/week (supervised)	~70 min/ session	Load set by device, real-time feedback	VAS (stop if >5)	Yes	Group II: One-legged decline squat (25° board, 3×15 reps, backpack)	None
(Jonsson and Alfredson, 2005)	25° decline squats, 3×15 reps, twice daily	Backpack (gradual increase)	2×/day	90 reps/day	Load increased if pain-free	Pain allowed, increase load when pain eased	Yes	CT: Concentric training	4/9 tendons in CT group dropped out due to pain
(Kongsgaard et al., 2009)	Decline squats, 3×15 reps, 2×/day	Backpack (gradual)	2×/day	90 reps/day	Increase with pain decrease	VAS ≤ 3–5	Yes	CORT: Steroid injections + eccentric	None reported
(Knež and Hudetz, 2023)	Decline squats (17° board)	Backpack (gradual increase)	2×/day	90 reps/day	Increase if pain tolerated	VAS ≤ 5	Yes	25° decline board	No adverse events
(Lee et al., 2020)	Decline squats (25° board), 3×15 reps	Bodyweight → backpack (+5 kg)	2×/day	90 reps/day	Progress if VAS 4–5; reduce if >6–7	VAS before/ after	Yes	ESWT + eccentric	None reported
(Niering and Muehlbauer, 2023)	Eccentric squats (flat and decline board) + stretching	80% concentric– eccentric 1RM	2–3×/week	40–60 reps/week	Adjust load to fatigue	VAS ≤ 5	Yes	ALT therapy (balance, isometrics)	None reported
(Ruffino et al., 2021)	Heavy slow resistance: squats, leg press, hack squat	15–6 RM progression	3×/week	4 sets/exercise	Gradual load increase	Pain <4/10 post-exercise	Yes	Flywheel training	Muscle soreness only
(Sánchez-Gómez et al., 2022)	Decline squats + HMB supplementation	HMB 3 g/day	2×/day	30 reps/day	Progression if VAS <4	VAS <4 for progression	Yes	Placebo supplementation	None reported
(Gómez et al., 2023)	Decline squats (daily)	Weight vest (5 kg) if VAS <3	6×/week	30 reps/day	Increase with vest if pain ≤3	VAS ≤3	No	N/A	Muscle soreness only
(van Ark et al., 2016)	Isometric vs isotonic leg extension	80% MVC (iso), 80% 8RM (isoT)	4×/week	5×45s (iso); 4×8 reps (isoT)	Increase load 2.5% weekly	NRS	Yes	Isometric vs isotonic	None reported
(Visnes et al., 2005)	Decline squats (25° board), 3×15 reps, 2×/day	Bodyweight → backpack (+5 kg)	2×/day	90 reps/day	Load increase if pain ≤3–4; reduce if ≥6–7	Target pain ≈5/10 tolerated	Yes	Control: training only	None reported
(Young et al., 2005)	Decline vs step squats	Bodyweight → backpack (+5 kg)	2×/day	90 reps/day	Decline: add load if pain eased; Step: progress speed then load	Decline: moderate pain allowed; Step: minimal pain only	Yes	Step group	None reported
Achilles Tendon
(Alfredson et al., 1998)	Heel drops, straight knee (gastroc) & bent knee (soleus); eccentric only	Bodyweight → backpack weights → weight machine if needed	2×/day, 7d/wk	3×15 reps for each exercise (2 variations)	Progressive overload when pain subsided	Pain VAS during running	Yes	Surgical treatment + postop rehab (12m follow-up)	Muscle soreness only
(Demir Benli et al., 2022)	Alfredson protocol: 3×15 reps, 2×/day, 12w	Bodyweight → backpack weights	2×/day	3×15 reps	Progress load if tolerated, pain <5/10	VAS	Yes	Group 2: ESWT (4 weekly sessions)	None reported
(Beyer et al., 2015)	Eccentric heel drops (straight and bent knee)	Bodyweight → backpack (1 kg every 2w)	2×/day	3×15 reps	Gradual increase as pain diminished	VAS (during activity)	Yes	Group 2: HSR (3×/week, heavy resistance)	One tendon rupture (ECC group)
(Habets et al., 2021)	Alfredson protocol (heel drops, straight + bent knee)	Bodyweight → backpack (+5 kg)	2×/day	180 reps/day	Load increased when pain-free	Pain allowed unless disabling	Yes	SG: Silbernagel program (concentric–eccentric progression + plyometrics)	One dropout (SG group)
(Knobloch et al., 2007)	Eccentric heel drops + AirHeel wrap	Backpack (5–10 kg)	2×/day	90 reps/day	Load increase if tolerated	VAS ≤ 5	Yes	Eccentric only (no AirHeel)	None reported
(Knobloch et al., 2008)	Same as above	Backpack (5–10 kg)	2×/day	90 reps/day	Load increase if tolerated	VAS ≤ 5	Yes	Eccentric only (no AirHeel)	None reported
(Langberg et al., 2007)	Heel drops (straight/ bent knee)	Backpack (+20% BW)	2×/day	90 reps/day	Increase if tolerated	VAS ≤ 3–5	Yes	Healthy tendon comparison	None reported
(Malliaras et al., 2013)	Standard eccentric (80% concentric–eccentric 1RM) vs high-load eccentric (80% eccentric 1RM)	80% 1RM	3×/week	45–60 reps/week	Load adjusted to fatigue	Pain monitored; stop if intolerable	Yes	Control: no exercise	None reported
(Radovanović et al., 2022)	Alfredson protocol vs high-load isometric plantarflexion	Alfredson: progressive load (5 kg/wk)	2×/day	45 reps/day (Alfredson); 4×4 reps (High-load)	Load progression if NRS <6, exertion <3	NRS	Yes	Passive therapy (no loading)	None reported
(Rompe et al., 2007)	Heel drops, 3×15 reps, twice daily	Bodyweight → backpack (5 kg)	2×/day	45 reps/day	Load increased when pain subsided	Pain should remain mild/moderate	Yes	SWT (radial shock-wave therapy)	None reported
(Rompe et al., 2009)	Heel drops, 3×15 reps, twice daily	Bodyweight → 5 kg rucksack	2×/day	45 reps/day	Load increased when pain subsided	Pain mild/ moderate only	Yes	Eccentric + SWT	None reported
(Stergioulas et al., 2008)	Decline squats (progress to backpack load)	Weight vest (4 kg)	4×/week	144 reps/week	Progress load if VAS <50 mm	VAS <50 mm	Yes	Placebo laser	None reported
Hamstring tendon
(Verma et al., 2022)	HPLT monotherapy	Laser (50 J/cm2, 5W)	3×/week	6 min/session	Fixed (dose-based)	NPRS	Yes	Conventional: US + heat + Nordic hamstring eccentrics	None reported

ADL = Activities of Daily Living; ALT = Alternative Therapy; BW = Bodyweight; CMJ = Countermovement Jump; CON = Control group; CONC = Concentric; CT = Concentric Training; ECC = Eccentric; EMG = Electromyography; ESWT = Extracorporeal Shock Wave Therapy; FAOS = Foot and Ankle Outcome Score; HMB = β-Hydroxy β-Methylbutyrate; HPLT = High-Power Laser Therapy; HSR = Heavy Slow Resistance; IFC = Interferential Current Therapy; IPT = Isokinetic Peak Torque; KOOS = Knee Injury and Osteoarthritis Outcome Score; MVC = Maximal Voluntary Contraction; NRS = Numeric Rating Scale; NPRS = Numeric Pain Rating Scale; PT = Patellar Tendinopathy; PTLE = Progressive Tendon-Loading Exercise; RM = Repetition Maximum; SG = Silbernagel Program; SLDS = Single-Leg Decline Squat; SWT = Shock Wave Therapy; US = Ultrasound; USGET = Ultrasound-Guided Galvanic Electrolysis Technique; VAS = Visual Analog Scale; VISA-A = Victorian Institute of Sport Assessment–Achilles; VISA-P = Victorian Institute of Sport Assessment–Patella; WP = Without Pain group.

Training frequency was consistently high, with the majority prescribing two daily sessions, 7 days per week following the Alfredson or decline squat model (Alfredson et al., 1998; Visnes et al., 2005; Jonsson and Alfredson, 2005; Bahr et al., 2006). Alternative approaches reduced frequency to 3 sessions per week in heavy slow resistance programs (Beyer et al., 2015; Ruffino et al., 2021) or supervised gym-based regimens (Cannell et al., 2001; van Ark et al., 2016). Training volumes typically amounted to 3 sets of 15 repetitions per exercise, leading to ~90 reps/day in most eccentric-only models, while heavy resistance protocols varied intensity through progressive loading based on percentage of 1RM (repetition maximum) or RM ranges (15RM → 6RM) (Malliaras et al., 2013; Ruffino et al., 2021). Pain monitoring was an integral feature of nearly all protocols, with eccentric programs generally allowing participants to exercise into moderate pain (VAS 4-5/10) as part of progression (Visnes et al., 2005; Jonsson and Alfredson, 2005; Bahr et al., 2006), whereas comparator protocols (e.g., isotonic or isometric training) emphasized pain minimization (VAS <3/10) (van Ark et al., 2016; Sánchez-Gómez et al., 2022).

Critical appraisal within sources of evidence

Across the 29 randomized trials (Table 6), the most frequent source of bias was lack of blinding of participants and reliance on self-reported outcomes such as VISA-P/VISA-A and pain scores. In nearly all studies, interventions were obvious - e.g., eccentric decline squats (Jonsson and Alfredson, 2005; Visnes et al., 2005), heavy slow resistance (Kongsgaard et al., 2009; Beyer et al., 2015), extracorporeal shockwave therapy (Rompe et al., 2007; Rompe et al., 2009), and adjuvant modalities like low-level laser (Stergioulas et al., 2008) - making patient blinding impossible. This inevitably creates “some concerns” in the domains of deviations from intended interventions and measurement of the outcome, since participants’ expectations and therapists’ involvement may have influenced adherence and reporting in many trials (e.g., Bahr et al., 2006; Abat et al., 2016; Lee et al., 2020; Habets et al., 2021; Ruffino et al., 2021). A rare counter-example was Malliaras et al. (2013), which achieved low risk across all domains.

Table 6.

Risk of bias in randomized controlled trials.

Study	Randomization process	Deviations from intended interventions	Missing outcome data	Measurement of outcome	Selection of reported result	Overall RoB
(Abat et al., 2016)	Low risk	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Bahr et al., 2006)	Low risk	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Demir Benli et al., 2022)	Low risk	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Beyer et al., 2015)	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Biernat et al., 2014)	High risk	Some concerns	Low risk	Some concerns	Some concerns	High risk
(Breda et al., 2021)	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Cannell et al., 2001)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Cunha et al., 2012)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Frohm et al., 2007)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Habets et al., 2021)	Some concerns	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Jonsson and Alfredson, 2005)	Some concerns	Some concerns	High risk	Some concerns	Some concerns	High risk
(Knež and Hudetz, 2023)	Low risk	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Knobloch et al., 2007)	Some concerns	Some concerns	High risk	Some concerns	Some concerns	High risk
(Knobloch et al., 2008)	Low risk	Some concerns	Some concerns	Some concerns	Some concerns	Some concerns
(Kongsgaard et al., 2009)	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Langberg et al., 2007)	High risk	Some concerns	Low risk	Some concerns	Some concerns	High risk
(Lee et al., 2020)	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Malliaras et al., 2013)	Low risk	Low risk	Low risk	Low risk	Low risk	Low risk
(Niering and Muehlbauer, 2023)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Radovanović et al., 2022)	Some concerns	Some concerns	Low risk	Low risk	Low risk	Some concerns
(Rompe et al., 2007)	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Rompe et al., 2009)	Low risk	Some concerns	Low risk	Some concerns	Low risk	Some concerns
(Ruffino et al., 2021)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Stergioulas et al., 2008)	Low risk	Some concerns	Some concerns	Low risk	Some concerns	Some concerns
(van Ark et al., 2016)	Low risk	Some concerns	Some concerns	Some concerns	Some concerns	Some concerns
(Verma et al., 2022)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns
(Visnes et al., 2005)	Low risk	Some concerns	Some concerns	Some concerns	Some concerns	Some concerns
(Young et al., 2005)	Some concerns	Some concerns	Low risk	Some concerns	Some concerns	Some concerns

Another common issue was selective reporting and trial registration, especially in older studies. Several trials conducted before 2010, such as Visnes et al. (2005), Jonsson and Alfredson (2005), and Knobloch et al. (2007), had no preregistration and limited outcome justification, resulting in some concerns or high risk in the “selection of reported results” domain. Conversely, modern trials like Demir Benli et al. (2022) and Knež and Hudetz (2023) reported robust randomization, balanced attrition, and registration, leaving only performance/measurement bias as residual concerns.

Both non-randomized studies (Table 7) were judged to be at serious overall risk of bias. In Alfredson et al. (1998) concerns arose from reliance on unblinded self-reported outcomes, placing outcome measurement at serious risk of bias. In Gómez et al. (2023), although objective measures such as echography and performance tests were included, the small sample size, absence of blinding, and concurrent athletic participation contributed to moderate to serious concerns. Across both studies, selective reporting could not be excluded due to the absence of preregistered protocols.

Table 7.

Risk of bias of the non-randomized controlled trials.

ROBINS-I Domain	(Alfredson et al., 1998)	(Gómez et al., 2023)
Bias due to confounding	Serious	Serious
Bias in selection of participants into the study	Moderate	Moderate
Bias in classification of interventions	Low	Low
Bias due to deviations from intended interventions	Moderate	Moderate
Bias due to missing data	Low	Low
Bias in measurement of outcomes	Serious	Moderate
Bias in selection of the reported result	Moderate	Moderate

Results of individual sources of evidence

Across patellar tendinopathy studies (Table 8), eccentric loading consistently reduced pain and improved function (Jonsson and Alfredson, 2005; Knež and Hudetz, 2023), with HSR providing comparable or superior long-term outcomes (Kongsgaard et al., 2009; Ruffino et al., 2021). Adjunctive modalities such as US-guided galvanic electrolysis, ESWT, or supplementation accelerated early symptom relief in some cases - typically within the first 4-6 weeks (up to 8 weeks in some protocols) - although in-season interventions often showed limited short-term functional gain, with no meaningful improvements across the 0-12-week competitive-season period (Abat et al., 2016; Lee et al., 2020; Sánchez-Gómez et al., 2022; Visnes et al., 2005). Most programs demonstrated high return-to-sport (RTS) rates (Cannell et al., 2001; Bahr et al., 2006), while performance improvements were variable (Biernat et al., 2014; Niering and Muehlbauer, 2023). Structural responses favored high-load resistance with reduced neovascularization and enhanced tendon quality (Kongsgaard et al., 2009), though remodeling was inconsistent in other protocols (Lee et al., 2020). Overall, exercise-based care was safe and well tolerated, with occasional discomfort and low dropout except when using concentric-only loading (Jonsson and Alfredson, 2005).

Table 8.

Synthesis of the main findings for Pattelar tendon.

Study	Pain Outcomes	Function Outcomes	Performance / RTS	Tendon Structure / Physiology	Safety / Adherence
(Abat et al., 2016)	Pain not separated from VISA-P.	VISA-P ↑ in both arms. USGET+ECC higher success (72.4% vs 36.1%, χ2=10.3, p=0.001). Subgroup Δ (VISA-P<90): MD +10.1 (95% CI 6.3–13.8, p<0.001). Subgroup Δ (≥90): MD +29.2 (95% CI 13.4–24.7, p<0.001).	RTS not directly assessed. “Healed” defined as VISA-P ≥90; 50% healed at 28–56 d with USGET (2–4 sessions). At 42 d: 58.7% healed (USGET) vs 12.5% (Electro-physio), p<0.01.	Not assessed.	No AEs; withdrawals NR.
(Bahr et al., 2006)	VAS0–10 during tests ↓ in both at 12m (all p<0.01); no between-group diff.	VISA-P ≈30→70 by 12m in both; no between-group diff (ANOVA p=0.87).	No jump/leg-press between-group diff; both ↑ strength to 12m. RTS distributions similar at 12m.	Not assessed.	One post-op quad pain; 25% ECC knees crossed to surgery.
(Biernat et al., 2014)	Pain reflected by VISA-P.	VISA-P ↑ with ECC (85→90 at 24w, p<0.05 vs control). Control ~NS.	Jump height / power: NS. RTS NR.	US: trend to fewer morph changes / neovasc in ECC.	No AEs; no dropouts.
(Breda et al., 2021)	Pain during tendon-specific exercise at 24w: PTLE 2 vs EET 4; diff=2 (95% CI 1–3), p=0.006.	VISA-P: BL 55 both. 24w: PTLE 84 vs EET 75 (p=0.023). MCID (≥13): 87% vs 77% (NS).	RTS: 24w 43% (PTLE) vs 27% (EET) (NS).	Imaging collected; results in supplement.	Satisfaction “excellent” higher with PTLE (38% vs 10%, p=0.009). No serious AEs.
(Cannell et al., 2001)	VAS0–10 ↓ both arms over 12w (p<0.01); NS between groups.	No VISA used.	RTS: 90% (drop squat) vs 67% (leg ext/curl) at 12w (NS). Strength: quads NS; hamstrings ↑ both (p<0.001).	Not assessed.	All completed ≥55/60 sessions; no AEs.
(Cunha et al., 2012)	VAS0–10: ECC-with-pain and ECC-pain-free both ↓ at 8w/12w (p<0.05); NS between groups.	VISA-P ↑ both (p<0.05); NS between groups.	RTS NR.	Not assessed.	17→14 completed.
(Frohm et al., 2007)	VAS0–10: Device 4→0 (p=0.003); Decline 5→1 (p=0.008); NS between groups.	VISA-P: Device 49→86; Decline 36→75 (both p<0.001).	One-leg triple hop ↑ both (p<0.001). RTS: majority resumed.	Not reported.	No AEs; full adherence.
(Jonsson and Alfredson, 2005)	VAS0–100: ECC 73→23 (p<0.005); CONC 74→68 (NS).	VISA-P: ECC 41→83 (p<0.005); CONC 41→37 (NS).	RTS: 9/10 tendons (ECC) satisfied & returned by 12w; 0/9 (CONC); all CONC later needed surgery/sclerosing. ~32m FU: ECC VAS ~18; VISA-P ~88.5.	Not assessed.	CONC had dropouts due to pain; ECC tolerated.
(Kongsgaard et al., 2009)	VAS0–10: all ↓ at 12w; at 6m, CORT deteriorated; ECC maintained; HSR best (lower pain vs CORT, p<0.05)	VISA-P: all ↑ at 12w; at 6m, CORT regressed; ECC stable; HSR highest (HSR > CORT; ECC > CORT, p<0.05)	Satisfaction at 6m highest in HSR (73%)	Thickness ↓ in CORT & HSR; Doppler ↓ CORT & HSR; collagen turnover ↑ only in HSR (↑HP/LP, ↓pentosidine). Mechanics unchanged.	No AEs; adherence high.
(Niering and Muehlbauer, 2023)	Pain-related training interruptions: ALT fewer (0.1±0.3 vs 1.3±1.3; p=0.002, d=1.16).	Physical performance improved in both; CODS improved more in ALT (left-leg interaction p=0.007).	ALT shorter program (47±16 d vs 58±25 d).	Structure not assessed.	Injury incidence lower in ALT (p=0.023, d=0.82). Attendance ALT 96% vs CON 89%.
(Ruffino et al., 2021)	Provocative VAS0–10 ~7→~3 at 12w both; NS between groups.	VISA-P: ↑ both; NS between groups at 6/12w. PSFS ↑ both; EQ-5D / EQ-VAS ↑ both.	CMJ, hop, strength tests improved similarly; RTS NR.	Patellar AP diameter unchanged; neovasc distributions converged by 12w; NS between groups.	Adherence high (88–90%); no AEs.
(Sánchez-Gómez et al., 2022)	VISA-P: NS over time (p=0.202).	— (same as pain).	CMJ ↑ (35.3→39.5 cm, p=0.031). Back squat: PPKG ↑ (55.0→73.6 kg, p=0.033); PP ↑ POST vs PRE (p=0.037, overall trend p=0.060); PPMV NS. 5-RM ↑ (60.4→75.4 kg, p=0.001).	US: thickness ↓ injured (7.74→5.69 mm, p=0.045); side-to-side diff resolved by POST.	~5.6 sessions/wk; no AEs.
(Gómez et al., 2023)	VISA-P / pain: NS for intervention, supplement, or interaction.	—	CMJ: significant intervention×supplement (HMB ↑ ~+3 cm, p=0.049). Back squat: PPKG ↑ overall (p=0.028). PPPP ↑ only in HMB (p=0.049). 5-RM ↑ both groups (p=0.001). PPMV NS.	Body comp: NS.	No AEs; small n=8; full adherence.
(van Ark et al., 2016)	NRS0–10 during SLDS: Isometric 6.3→4.0 (p=0.012); Isotonic 5.5→2.0 (p=0.003); NS between groups.	VISA-P: Isometric 66.5→75.0 (p=0.028); Isotonic 69.5→79.0 (p=0.003); NS between groups.	Athletes maintained full in-season loads; GRC +2.3 (improved).	Not assessed.	Median 3 sessions/wk (~81%); no AEs.
(Visnes et al., 2005)	VISA-P: no change ECC (71.1→70.2, NS) or control (76.4→75.4, NS); transient week-1 pain dip only.	Global knee function: NS between groups.	Jump tests: small within-group CMJ both-legs +1.2 cm (p=0.046); other tests NS; no RTS advantage.	Not assessed.	ECC compliance ~59% of prescription; low external load; one new PFP case; otherwise safe.
(Young et al., 2005)	VAS0–100: both improved at 12w & 12m (both p<0.05). At 12w step more likely ↓ pain; at 12m groups similar.	VISA-P: both improved at 12w & 12m (both p<0.05). 12m: decline squat had higher likelihood of ≥20-pt gain (94% vs 41%).	Athletes trained/competed; decline showed more durable functional benefit at 12m.	Not assessed.	Compliance ~72%; no AEs.

ADL: activities of daily living; AE: adverse event; AG: Alfredson group; ALT: alternative therapy; AP: anteroposterior; ACSA: anatomical cross-sectional area; AT: Achilles tendinopathy; BL: baseline; CA: color area (Doppler neovascularity); CMJ: countermovement jump; CODS: change-of-direction speed; CON: conventional therapy; CONC: concentric exercise; CORT: corticosteroid injection; CSA: cross-sectional area; DJ: drop jump; Doppler: power/color Doppler ultrasound; ECC: eccentric exercise; EET: eccentric exercise therapy; EOT: end of treatment; ESWT: extracorporeal shock-wave therapy; FAOS: Foot and Ankle Outcome Score; FU: follow-up; GPE: global perceived effect; GRC: global rating of change; HMB: β-hydroxy β-methylbutyrate; HPLT: high-power laser therapy; HP/LP: hydroxylysyl-/lysyl-pyridinoline ratio; HSR: heavy slow resistance; ICTP: carboxy-terminal telopeptide of type-I collagen; IP: intrapatient; IPT: isokinetic peak torque; IQR: interquartile range; KOOS: Knee injury and Osteoarthritis Outcome Score; LLLT: low-level laser therapy; MD: mean difference; m/M: months; MVC: maximal voluntary contraction; MVIC: maximal voluntary isometric contraction; N/A or NR: not assessed / not reported; NRS or NPRS: numeric (pain) rating scale (0–10); NS: not significant; P-CSA: patellar tendon cross-sectional area; PFP: patellofemoral pain; PICP: procollagen type-I C-terminal propeptide; PP: peak power; PPKG: load at peak power (kg); PPMV: mean velocity at peak power; PPPP: peak power in watts; PT: patellar tendinopathy; PTLE: progressive tendon-loading exercise; PHT: proximal hamstring tendinopathy; QoL: quality of life; rHb: postcapillary venous filling pressure (relative hemoglobin); RTS: return to sport; SG: Silbernagel group; SLDS: single-leg decline squat; StO₂: tissue oxygen saturation; SWT: shock-wave treatment; US: ultrasound; USGET: ultrasound-guided electrolysis therapy (as named in Abat 2016); VAS0–10: visual analogue scale 0–10; VAS0–100: visual analogue scale 0–100 mm; VISA-A: Victorian Institute of Sport Assessment—Achilles; VISA-P: Victorian Institute of Sport Assessment—Patella; wk/w: week(s). Symbols — ↑: increase; ↓: decrease; →: to; ≈: approximately.

For Achilles tendinopathy (Table 9), eccentric approaches demonstrated consistent analgesic and functional benefits across populations (Alfredson et al., 1998; Habets et al., 2021), while HSR achieved similar or sometimes superior long-term results (Beyer et al., 2015). Adjuncts such as ESWT and laser therapy were effective when combined with exercise but showed less uniform benefits alone (Stergioulas et al., 2008; Rompe et al., 2009). Return-to-activity outcomes were strong (Alfredson et al., 1998) and comparable to surgical interventions without the associated risk profile (Bahr et al., 2006). High-load protocols led to the greatest structural and physiological adaptations, including improved collagen turnover and stiffness (Langberg et al., 2007; Radovanović et al., 2022), while bracing improved microcirculation (Knobloch et al., 2007, 2008). Across studies, interventions were safe, with transient soreness the most common adverse effect.

Table 9.

Synthesis of the main findings for Achilles tendon.

Study	Pain Outcomes	Function Outcomes	Performance / RTS	Tendon Structure / Physiology	Safety / Adherence
(Alfredson et al., 1998)	VAS0–100 during activity: ECC 81.2→4.8 at 12w (p<0.001); comparator 71.8→21.2 at 24w (p<0.01). Between-group: ECC faster/larger ↓.	No VISA.	RTS: 100% ECC back to pre-injury running at 12w. Strength deficits at BL resolved after ECC.	NR.	No AEs with ECC.
(Demir Benli et al., 2022)	VAS0–10: at 3m both ≈2.6; NS between groups. At 2y: ECC 1.2 (↑, p<0.001) vs ESWT 5.4 (NS) → long-term benefit only with ECC.	VISA-A: both ↑ to ≈80 at 3m (both p<0.001), NS between groups.	RTS not direct; “recovery” 81% ECC vs 77% ESWT at EOT.	US: thickness ↑ with ECC (4.7→5.2 mm, p=0.002); stiffness ↑ (strain ratio 2.1→3.1, p=0.039); ESWT NS. Neovasc: NS.	63/63 completed; no major AEs.
(Beyer et al., 2015)	VAS0–10 (running, heel-rise) ↓ 0–12w, maintained 52w (both p<0.0001); NS between ECC and HSR.	VISA-A: ECC 58→84; HSR 54→89 (time p<0.0001); NS between groups.	Activity level ↑ modestly; RTS NR.	US: thickness ↓ both (p<0.001). Doppler ↓ both (time p<0.005).	Satisfaction 12w higher in HSR (100% vs 80%, p=0.052); adherence: ECC 78% vs HSR 92% (p<0.005). No major AEs.
(Habets et al., 2021)	VAS0–100 ADL: AG 28.6→5.8; SG 28.6→9.0 (both p=0.004); NS between groups. Sports: AG 44.8→13.1; SG 46.6→12.8 (both p=0.027); NS.	VISA-A: AG 60.7→89.4; SG 59.8→83.2 (both p<0.001). NS treatment effect (2.4; 95% CI −8.5 to 13.3; p=0.656).	GPE: more “improved” in SG (77% vs 50%, p=0.04). RTS NR.	NR.	Adherence high (AG 74%, SG 77%). One SG dropout after race.
(Knobloch et al., 2007)	VAS0–10: Wrap+ECC 5.1→3.2 (−37%, p=0.0001); ECC 5.5→3.6 (−35%, p=0.0001); NS between groups.	FAOS: both ↑; larger % gains with Wrap+ECC (all p≤0.006 vs ECC).	RTS NR; FAOS-Sport ↑ more with Wrap+ECC.	Microcirculation: Wrap+ECC StO2 ↑, venous pressure ↓ more vs ECC; capillary flow patterns differed.	81% completed; no AEs.
(Knobloch et al., 2008)	VAS0–10: Wrap+ECC 5.1→2.9 (−43%, p=0.0001); ECC 5.4→3.6 (−33%, p=0.0001); NS at final.	FAOS: ↑ both; no between-group diff at end.	RTS NR.	Wrap+ECC: StO2 ↑ tendon & paratendon; venous pressure ↓ broadly. ECC alone: limited microvascular change.	Safe; no AEs.
(Langberg et al., 2007)	VAS0–100: injured 44→13 after 12w ECC (p<0.05).	—	RTS: all 6 injured elite soccer players returned.	Microdialysis: collagen synthesis ↑ (PICP 3.9→19.7 μg/L, p<0.05) in injured; no change healthy; degradation (ICTP) unchanged.	100% adherence; no AEs.
(Malliaras et al., 2013)	— (no symptoms)	—	Strength: 5RM ↑ all groups; greatest in High-load ECC.	Tendon: modulus/stiffness ↑ all at 50–75% MVIC; only High-load ECC ↑ at 75–100% MVIC. CSA unchanged.	Training pain ~1.3–2.0% sessions; no consequential AEs.
“center”>(Radovanović et al., 2022)	NRS0–10: modest ↓ all (−0.55±0.9, p<0.001); NS between groups.	VISA-A: ↑ ≈+20 pts in all (time p<0.001; no interaction).	High-load only: MVC ↑7% (p=0.045). CMJ ↓ slightly all.	High-load only: stiffness ↑20% (p=0.049), CSA ↑9% (p<0.001), max strain ↓12% (p=0.001); modulus NS.	Compliance similar (80–90%); no AEs.
(Rompe et al., 2007)	NRS0–10: ECC 7.0→3.6; SWT 6.8→4.0; Wait 7.9→5.9. ECC & SWT > Wait (p<0.001); ECC vs SWT NS.	VISA-A: ECC 51→76; SWT 50→70; Wait 48→55. ECC & SWT > Wait (p<0.001); ECC vs SWT NS.	Likert recovery 1–2: 60% (ECC), 52% (SWT), 24% (Wait).	Tendon diameter: no change.	Minor transient effects only; no ruptures.
(Rompe et al., 2009)	NRS0–10: ECC 7.0→3.9; ECC+SWT 6.8→2.4; between-group −1.5 (95% CI 0.5–2.5, p=0.0045).	VISA-A: ECC 51→73; ECC+SWT 50→87; between-group +13.5 (p=0.0016).	Likert 1–2: 56% vs 82% (p=0.001). At 12m, differences diminished due to crossovers/surgeries.	NR.	Minor transient effects; analgesic use associated with failure.
(Stergioulas et al., 2008)	VAS0–100 during activity: LLLT better at 4w (53.6 vs 71.5, p=0.0003), 8w (37.3 vs 62.8, p=0.0002), 12w (33.0 vs 53.0, p=0.007).	Secondary function: morning stiffness ↓, dorsiflexion ↑, palpation tenderness/crepitation ↓ more with LLLT (all p<0.05).	RTS NR; clinical recovery accelerated (LLLT 4w ≈ placebo 12w).	NR.	High adherence; 4 transient calf aches resolved; no serious AEs.

ADL: activities of daily living; AE: adverse event; AG: Alfredson group; ALT: alternative therapy; AP: anteroposterior; ACSA: anatomical cross-sectional area; AT: Achilles tendinopathy; BL: baseline; CA: color area (Doppler neovascularity); CMJ: countermovement jump; CODS: change-of-direction speed; CON: conventional therapy; CONC: concentric exercise; CORT: corticosteroid injection; CSA: cross-sectional area; DJ: drop jump; Doppler: power/color Doppler ultrasound; ECC: eccentric exercise; EET: eccentric exercise therapy; EOT: end of treatment; ESWT: extracorporeal shock-wave therapy; FAOS: Foot and Ankle Outcome Score; FU: follow-up; GPE: global perceived effect; GRC: global rating of change; HMB: β-hydroxy β-methylbutyrate; HPLT: high-power laser therapy; HP/LP: hydroxylysyl-/lysyl-pyridinoline ratio; HSR: heavy slow resistance; ICTP: carboxy-terminal telopeptide of type-I collagen; IP: intrapatient; IPT: isokinetic peak torque; IQR: interquartile range; KOOS: Knee injury and Osteoarthritis Outcome Score; LLLT: low-level laser therapy; MD: mean difference; m/M: months; MVC: maximal voluntary contraction; MVIC: maximal voluntary isometric contraction; N/A or NR: not assessed / not reported; NRS or NPRS: numeric (pain) rating scale (0–10); NS: not significant; P-CSA: patellar tendon cross-sectional area; PFP: patellofemoral pain; PICP: procollagen type-I C-terminal propeptide; PP: peak power; PPKG: load at peak power (kg); PPMV: mean velocity at peak power; PPPP: peak power in watts; PT: patellar tendinopathy; PTLE: progressive tendon-loading exercise; PHT: proximal hamstring tendinopathy; QoL: quality of life; rHb: postcapillary venous filling pressure (relative hemoglobin); RTS: return to sport; SG: Silbernagel group; SLDS: single-leg decline squat; StO₂: tissue oxygen saturation; SWT: shock-wave treatment; US: ultrasound; USGET: ultrasound-guided electrolysis therapy (as named in Abat 2016); VAS0–10: visual analogue scale 0–10; VAS0–100: visual analogue scale 0–100 mm; VISA-A: Victorian Institute of Sport Assessment—Achilles; wk/w: week(s). Symbols — ↑: increase; ↓: decrease; →: to; ≈: approximately.

Evidence for proximal hamstring tendinopathy remains sparse (Table 10), but a combined protocol using high-power laser therapy with exercise demonstrated significant short-term reductions in pain and gains in strength in track-and-field athletes, with no reported complications (Verma et al., 2022). While early responses are promising, the lack of long-term and structural data limits definitive conclusions for this tendon site.

Table 10.

Synthesis of the main findings for hamstring tendon.

Study	Pain Outcomes	Function Outcomes	Performance / RTS	Tendon Structure / Physiology	Safety / Adherence
(Verma et al., 2022)	NPRS0–10: HPLT ↓61% (p≤0.001); Conventional ↓41% (p≤0.001). Between-group: HPLT better (p≤0.001).	IPT (isokinetic peak torque): HPLT ↑13% (p=0.028); Conventional +1.5% (NS); between-group NS (p=0.113).	RTS NR.	Not assessed.	No AEs; short protocol; compliance implied high.

AE: adverse event; VAS0–10: visual analogue scale 0–10; HPLT: high-power laser therapy; IPT: isokinetic peak torque.

Evidence Gap Map

To provide a visual overview of the research landscape, three evidence gap maps were constructed (Figure 2, Figure 3 and Figure 4). Figure 2 shows the distribution of studies by tendon site and sport type. The majority of evidence focuses on patellar tendinopathy in volleyball and basketball athletes and Achilles tendinopathy in running-related sports. Only a single study addressed proximal hamstring tendinopathy in track and field athletes (Verma et al., 2022), highlighting a clear evidence gap.

Figure 2.

Heatmap visualizing how commonly each clinical outcome domain is assessed at different tendon sites.

Figure 3.

Heatmap illustrating how often each tendon site is studied in athletes from various sports, with color intensity representing the number of cases.

Figure 4.

Relationship between intervention type and measured outcome domains. ECC: eccentric training.

Figure 3 summarizes tendon site versus outcome domains. Pain and function are the most consistently reported outcomes across both patellar and Achilles tendinopathy. In contrast, performance/return-to-sport and tendon structural/physiological adaptations are less frequently measured. Safety and adverse events were systematically reported in fewer studies, often limited to minor soreness or calf ache, indicating under-reporting of potential harms.

Figure 4 illustrates intervention type versus outcome domains. The majority of trials investigated eccentric-only protocols, while eccentric exercise combined with adjuncts such as heavy slow resistance, shockwave therapy, laser therapy, or electrolysis have become increasingly frequent. Multimodal rehabilitation programs remain less explored but tended to include structural and performance outcomes beyond pain and function.

Discussion

This scoping review synthesized evidence from 31 studies investigating eccentric training (ECC) for tendinopathies in athletic populations, spanning patellar, Achilles, and proximal hamstring tendinopathies, with most interventions involving competitive or elite athletes in volleyball, basketball, soccer, and track and field. While the majority were randomized controlled trials, sample sizes were often modest and protocols varied markedly in load progression, dosing frequency, and pain monitoring strategies. Comparator interventions ranged from surgery and heavy slow resistance (HSR) to shockwave therapy (ESWT), laser, or conservative physiotherapy, highlighting a broad translational context but complicating direct synthesis. Across outcomes, ECC consistently demonstrated reductions in pain and improvements in tendon-related function, with more heterogeneous findings for return-to-sport (RTS), athletic performance, and tendon structural remodeling. Adverse effects were infrequent and mild. Nevertheless, uncertainties remain regarding long-term durability, sport-specific reintegration, and standardized safety tracking.

Pattelar tendon

Evidence for patellar tendinopathy overwhelmingly supports eccentric loading as an effective intervention for reducing pain and improving tendon-related function in athletes, with clinically meaningful VISA-P gains reported in nearly all trials, including improvements from approximately 30-55 to 70-90 points within 12-24 weeks (Abat et al., 2016; Frohm et al., 2007; Breda et al., 2021; Knež and Hudetz, 2023). When compared directly with alternative exercise or conventional rehabilitation, eccentric training was consistently superior or equivalent, and greatly outperformed concentric training, which showed minimal improvement and poor tolerance (Jonsson and Alfredson, 2005). Multimodal or progressive loading programs such as progressive tendon-loading exercise revealed advantages over traditional eccentric exercise in reducing pain during tendon-loading tasks and promoting improvements in load tolerance, movement quality, lower-limb strength, and the ability to perform sport-specific tasks without symptom escalation (Breda et al., 2021). Performance outcomes were less consistent: some interventions increased jump performance, change-of-direction speed, and lower-limb strength (Frohm et al., 2007; Sánchez-Gómez et al., 2022; Niering and Muehlbauer, 2023), while others showed only small or nonsignificant changes despite clear clinical gains (Biernat et al., 2014). RTS was infrequently reported but generally favorable when included, with 67-90% return to sport by 12 weeks in studies using structured decline protocols (Cannell et al., 2001; Jonsson and Alfredson, 2005). Structural adaptations varied: high-load and injection-comparison studies revealed reductions in tendon neovascularity and improved collagen turnover (Kongsgaard et al., 2009), while others found symptomatic relief without remodeling (Lee et al., 2020), suggesting a potential disconnect between symptom change and tissue response. Importantly, adherence influenced outcomes -low compliance in some in-season studies may explain the absence of improvement (Visnes et al., 2005). Across the body of evidence, safety was strong, with no serious adverse events and withdrawals primarily linked to poorly tolerated concentric loading. These findings endorse eccentric and progressive tendon-loading programs as an effective cornerstone rehabilitation strategy in athletic patellar tendinopathy, particularly when external load is adequately progressed and adherence is supported.

Achilles tendon

Midportion Achilles tendinopathy research demonstrated highly consistent pain relief and VISA-A improvements with eccentric heel-drop protocols across recreational and competitive athletes, with typical improvements of 30-40 VISA-A points over 12 weeks (Alfredson et al., 1998; Habets et al., 2021; Rompe et al., 2007). Although ESWT and other adjuncts yielded short-term benefits when combined with exercise (Rompe et al., 2009; Stergioulas et al., 2008), ECC and HSR produced greater or more durable clinical change, with the latter showing the highest patient satisfaction and adherence (Beyer et al., 2015; Radovanović et al., 2022). Return-to-sport outcomes were favorable where reported - Alfredson et al. (1998) demonstrated 100% return to running by 12 weeks - yet most trials failed to track long-term RTS consistency or match recovery timelines to competitive calendars. Performance capacity was seldom evaluated, though selective studies noted strength or maximum voluntary contraction improvements with high-load protocols (Radovanović et al., 2022). Tendon structure and physiology responses differed by loading strategy: conventional ECC improved symptoms more than morphology, while high-load training demonstrated superior improvements in tendon stiffness, collagen turnover markers, and cross-sectional area, aligning with a mechanotransduction-driven restoration of tendon capacity (Langberg et al., 2007; Radovanović et al., 2022; Malliaras et al., 2013). Importantly, ESWT alone did not significantly alter tendon structure despite reducing symptoms (Rompe et al., 2007), underlining that structural recovery is load-dependent. Adherence remained high across studies, and adverse effects were minimal, typically limited to transient soreness. The Achilles literature therefore presents a mature evidence base supporting ECC and progressive loading strategies for pain and function, while highlighting critical ongoing gaps in performance return, season-specific rehabilitation design, and long-term tendon health monitoring.

Hamstring tendon

The evidence for proximal hamstring tendinopathy in athletes is notably sparse, with only one included controlled trial meeting criteria. The findings suggest that an eccentric-informed protocol integrating high-power laser therapy promotes meaningful reductions in pain and improvements in hamstring strength, while the comparator program produced more modest change (Verma et al., 2022). Although these outcomes indicate that tendon loading can be beneficial for PHT, the trial did not evaluate VISA-style function metrics, jump or performance outcomes, RTS, or tendon structural adaptation, limiting interpretation. Moreover, follow-up did not extend beyond the short post-intervention phase, and sample size was small with no imaging verification of tendon change. Given the high recurrence risk and major performance implications of PHT in sprinting and change-of-direction sports, the lack of robust evidence represents a concerning gap. High-quality randomized trials including season-specific outcomes and tendon capacity measures are urgently required.

Study limitations and practical implications

The heterogeneity of ECC prescriptions - spanning frequency, external load, progression rules, and pain-monitoring - hinders the ability to define optimal dosing for athletes. Outcome reporting prioritized pain and VISA measures, while RTS measures, tendon remodeling, and performance capacity were inconsistently collected despite their importance for athletic return and reinjury prevention. Most studies enrolled young male athletes, limiting generalization to female athletes, older competitors, or athletes in endurance or collision sports. Methodological limitations included limited blinding, short follow-up, inadequate adherence reporting, and insufficient monitoring for adverse events and reinjury. Research should prioritize long-term, sport-focused RCTs with clear RTS criteria, sex-balanced recruitment, and standardized tendon-loading parameters. Improved reporting of structural adaptation, intervention fidelity, safety, and athletic performance is needed. Comparative and multimodal studies may clarify optimal loading strategies and personalization of tendon rehabilitation in high-performance sport.

Despite the limitations, ECC remains a safe, accessible, and effective first-line treatment for patellar and Achilles tendinopathy in athletes, improving pain and function without interrupting participation for many cases. High-load resistance strategies (e.g., HSR) may enhance long-term outcomes and tendon mechanical properties. However, clinicians should supplement ECC with comprehensive RTS assessment, address sport-specific load demands, and tailor pain exposure and progression individually. Objective monitoring of performance and tendon health may help optimize rehabilitation and reduce recurrence risk. For under-studied tendon sites such as proximal hamstrings, evidence-based protocols cannot yet be standardized.

Conclusion

This scoping review shows that most research on eccentric training in athletes has concentrated on patellar tendinopathy (particularly in volleyball and basketball players) and Achilles tendinopathy (especially in running and soccer populations), with limited attention to other tendon sites. The main outcome domains analyzed were pain reduction, functional improvement, return-to-sport rates, performance outcomes, and tendon structural or physiological adaptations. Findings consistently support pain and functional improvements, with generally favorable return-to-sport outcomes, while evidence for performance enhancement and tendon remodeling remains inconsistent. Reporting on safety outcomes was limited, though adverse events were rare. Significant methodological gaps persist, including heterogeneity in exercise prescriptions, inconsistent progression strategies, and limited long-term follow-up. There is a particular need for standardization of training regimens and parameters - such as load, frequency, volume, and pain-monitoring criteria - to improve comparability across studies. Addressing these gaps with harmonized protocols and comprehensive outcome reporting will be essential for developing evidence-based, sport-specific recommendations for athletes with tendinopathy.

Biographies

Robert TRYBULSKI

Employment

Wojciech Korfanty Upper Silesian Academy, Katowice, Poland

Degree

PhD, PT

Research interests

Sports recovery methods, strength training, biomechanics, ultrasound musculoskeletal diagnostics, and post-exercise regeneration

E-mail: rtrybulski.provita@gmail.com

Gracjan OLANISZYN

Employment

Medical Department, Wojciech Korfanty Upper Silesian Academy, Katowice, Poland

Degree

MSc, PT

Research interests

Dry-needling, myofascial trigger point treatment, muscle tension and stiffness modulation

E-mail: gracjan.olaniszyn@wp.pl

Filip MATUSZCZYK

Employment

Provita Żory Medical Center, Żory, Poland

Degree

PT

Research interests

Rehabilitation techniques, biomechanical assessment, and exercise interventions for musculoskeletal and sports-related conditions

E-mail: filip.matuszczyk@o2.pl

Kamil GAŁĘZIOK

Employment

Provita Żory Medical Center, Żory, Poland

Degree

PT

Research interests

Therapeutic modalities for sports injuries, functional movement, and combining manual and instrumental techniques in rehabilitation

E-mail: kamilgaleziok00@gmail.com

Andryi VOVKANYCH

Employment

Department of Physical Therapy & Ergotherapy, Ivan Boberkyj Lviv State University of Physical Culture, Lviv, Ukraine

Degree

PT, PHD

Research interests

Ergotherapy interventions, exercise prescription, physical therapy for athletic populations, and cross-border collaboration in sports science

E-mail: avovkinfiz@i.ua

Yaroslav SVYSHCH

Employment

Ivan Boberkyj Lviv State University of Physical Culture, Lviv, Ukraine

Degree

PT, PHD

Research interests

Physical therapy and sports medicine

E-mail: yarsvysch@ukr.net