The Impact of the Degree of Kinesiophobia on Recovery in Patients With Achilles Tendinopathy

Abstract

Objective

Kinesiophobia has been proposed to influence recovery in individuals with Achilles tendinopathy. However, whether there are differences in outcomes in individuals with different levels of kinesiophobia is unknown. The purpose of this study was to compare the characteristics of patients at baseline and recovery over time in individuals with Achilles tendinopathy and various levels of kinesiophobia.

Methods

This study was a secondary analysis of a prospective observational cohort study of 59 individuals with Achilles tendinopathy. The participants were divided into 3 groups on the basis of scores on the Tampa Scale for Kinesiophobia (TSK) (those with low TSK scores [≤33; low TSK group], those with medium TSK scores [34–41; medium TSK group], and those with high TSK scores [≥42; high TSK group]). All participants were evaluated with self-reported outcomes, clinical evaluation, tendon morphology, viscoelastic property measurements, and a calf muscle endurance test at baseline, 6 months, and 12 months. No treatment was provided throughout the study period.

Results

There were 16 participants (8 women) in the low TSK group (age = 51.9 [SD = 15.3] years, body mass index [BMI] = 24.3 [22.3–25.4]), 28 participants (13 women) in the medium TSK group (age = 52.7 [SD = 15.2] years, BMI = 26.4 [22.5–30.8]), and 15 participants (8 women) in the high TSK group (age = 61.1 [SD = 11.1] years, BMI = 28.1 [25.2–33.6]). Among the groups at baseline, the high TSK group had significantly greater BMI and symptom severity and lower quality of life. All groups showed significant improvement over time for all outcomes except tendon viscoelastic properties and tendon thickening when there was an adjustment for baseline BMI. The high and medium TSK groups saw decreases in kinesiophobia at 6 months, but there was no change for the low TSK group.

Conclusion

Despite the high TSK group having the highest BMI and the worse symptom severity and quality of life at baseline, members of this group showed improvements in all of the outcome domains similar to those of the other groups over 12 months.

Impact

Evaluating the degree of kinesiophobia in individuals with Achilles tendinopathy might be of benefit for understanding how they are affected by the injury. However, the degree of kinesiophobia at baseline does not seem to affect recovery; this finding could be due to the patients receiving education about the injury and expectations of recovery.

Introduction

Achilles tendinopathy is an overuse injury that occurs in both active and inactive individuals.^1,2 Clinically, patients present with calf muscle weakness and pain and local or diffuse swelling at the Achilles tendon. Achilles tendon pain is provoked by physical activity, and therefore, individuals often limit their participation in exercise and sports.³ The symptoms and disability can persist for more than 1 year, and the long-term outcomes vary among individuals.⁴ Treating Achilles tendinopathy remains a challenge due to an incomplete understanding of what factors affect recovery.

A core outcome set of 9 tendon health–related domains has been established for tendinopathy research.⁵ In studies on Achilles tendinopathy, common outcomes are the Victorian Institute of Sports Assessment–Achilles (VISA-A) for pain and symptom severity,⁶ heel-rise test for calf muscle function,^7,8 and Tampa Scale of Kinesiophobia (TSK)⁹ for pain-related fear.¹⁰ In addition, tendon structure has been assessed and found to be useful for understanding the mechanism of tendon injury and recovery.^11–16 In individuals with Achilles tendinopathy, altered tendon structure such as tendon morphology and viscoelastic properties are related to injury severity and recovery.^16,17 Exercise-based treatment is the primary intervention of Achilles tendinopathy aimed at promoting tendon healing, recovery from impairment, and symptom relief. Accordingly, different levels of kinesiophobia may affect a person’s ability to exercise or reduce their level of physical activity and potentially influence the various outcome measures. Studies showed that the psychosocial aspect of the Achilles tendon injury has also been proposed to affect outcome.^16,18–20 To improve our understanding of factors involved in recovery, it is important to perform a comprehensive evaluation that includes both tendon structure and psychosocial aspects along with common measures of symptoms and calf muscle function in Achilles tendinopathy research.

Kinesiophobia, or irrational fear of movement, has been found to be associated with the recovery of painful injuries.^21,22 It is defined as “an excessive, irrational, and debilitating fear of physical movement and activity resulting from fear of painful injury or (re)injury.”⁹ The degree of kinesiophobia is often measured using the TSK.⁹ Because fear of movement may limit an individual’s activities^23,24 and eventually may restrict those with Achilles tendon pain from participation in sports activities,³ its influence on an individual’s ability to recover warrants further investigation. Tendon-loading exercises, despite being painful, are considered an essential part of treatment for Achilles tendinopathy.^25–29 The level of kinesiophobia might therefore also influence the compliance with the exercise treatment. In previous studies, we have found that the outcomes of individuals with Achilles tendinopathy were associated with kinesiophobia.^16,19 In individuals with back pain, a study reported that grouping people based on the level of kinesiophobia was helpful in understanding its influence on rehabilitation and recovery.³⁰ This model was developed based on data from various pain conditions and reference groups;^31–35 it might therefore be useful to test the model in the Achilles tendinopathy cohort to identify similar patterns in this group. Further study on grouping individuals with Achilles tendinopathy based on the level of kinesiophobia may help improve our understanding of its influence on symptom severity and recovery over time.

Therefore, the purpose of this observational study was to examine if there were differences in characteristics at baseline and recovery over time between individuals with different levels of kinesiophobia. Specifically, we hypothesized that those with a high level of kinesiophobia would be worse off at baseline and not recover to the same degree as the other groups in reference to symptoms, tendon morphology and viscoelastic properties, and calf muscle function. In addition, we wanted to evaluate if the level of kinesiophobia in the various groups changed over time.

Methods

Study Design and Participants

This is a secondary analysis of a prospective observational cohort study on individuals with Achilles tendinopathy. During the period from November 2014 and June 2018, 121 participants consented and were assessed throughout 1 year. The participants were evaluated at baseline and again after 6 and 12 months. The evaluations included clinical evaluation, functional assessments, and measurements of tendon morphology and viscoelastic properties. The research protocol for the prospective observational study was approved by the institutional review board at the University of Delaware.

The inclusion criteria for the current study were a minimum age of 18 years and being diagnosed with Achilles tendinopathy (midportion or insertional) (Suppl. Figure). Exclusion criteria were Achilles tendon rupture, or history of other musculoskeletal injuries or surgeries such as knee or hip arthroplasty, or chronic back pain. The participants also had to have attended the baseline visit and the 6- and 12-month follow-up visits. Because other musculoskeletal injuries may influence the level of fear of movement, we wanted to exclude those with multiple injuries. All participants underwent a thorough clinical examination by a licensed physical therapist. The criteria for the clinical diagnosis of Achilles tendinopathy were localized pain and stiffness in the Achilles tendon, either 2 to 6 cm proximal to the calcaneal insertion (midportion) or at the tendon-bone junction (insertional), and increased symptoms with loading.¹

Participant-Reported Outcome Measures

Participants were asked to complete questionnaires related to demographics, history of present illness, and 4 participant-reported outcomes: VISA-A,³⁶ Foot and Ankle Outcome Score (FAOS),³⁷ Physical Activity Scale (PAS),³⁸ and TSK at baseline, 6 months, and 12 months.

Tampa Scale of Kinesiophobia³⁹

The degree of kinesiophobia was measured by the TSK questionnaire, which consists of 17 questions with a total score ranging from 17 to 68. Grouping participants based on the level of kinesiophobia has been used in chronic back pain literature.³⁰ We followed the same method and classified the participants at baseline into 3 subgroups: those with low TSK scores (17–33) (low TSK group), those with medium TSK scores (34–41) (medium TSK group), and those with high TSK scores (42–68) (high TSK group).³⁰

Victorian Institute of Sports Assessment–Achilles³⁶

The VISA-A is a measurement tool designed for evaluating the pain and symptom severity in individuals with Achilles tendinopathy and is scored from 0 to 100, with high scores indicating lower disability and being pain free. Participants with bilateral symptoms were asked to complete the VISA-A for both sides, and the side with the lower score was selected as the most symptomatic side. Although we did collect data using the quality-of-life (QOL) subscale of the FAOS (FAOS-QOL), the FAOS is designed for evaluating outcomes in a broader patient population with injury to the foot and ankle, particularly ankle ligaments injury.³⁷ The VISA-A includes 3 questions on pain: pain intensity in the morning (morning stiffness), pain intensity during stretching, and pain intensity after walking. Recently, the VISA-A pain construct and VISA-A total score showed a fair to moderately strong negative relationship with self-reported pain in the single-heel hop test.⁴⁰ Lastly, kinesiophobia has been shown to have no relationship with self-reported pain in the loading test for both midportion and insertional Achilles tendinopathies.⁴⁰

Foot and Ankle Outcome Score³⁷

A region-specific instrument, FAOS, was used for evaluating symptoms, functional limitations, and foot- and ankle-related QOL.³⁷ It contains 42 items arranged in 5 subscales: pain, other symptoms, activities of daily living, sports and recreational activities, and foot- and ankle-related QOL. The score ranges from 0 to 100, with a score of 100 indicating a higher level of health and QOL from a foot and ankle perspective. In this study, only the FAOS-QOL was used.

Physical Activity Scale³⁸

The PAS is a 6-level scale questionnaire used to assess level of physical activity.³⁸ A grade of 1 equals no physical activity, whereas grade 6 matches hard or very hard exercises (eg, jogging) regularly and several times a week. Prior literature has used PAS for individuals with Achilles tendinopathy.^16,29,41

Measurements of Tendon Morphology and Viscoelastic Properties

Tendon Thickness and Degree of Thickening

To evaluate tendon thickness, we used B-mode ultrasound imaging (10 MHz) with a LOGIQ e Ultrasound System (GE Healthcare, Chicago, IL, USA) and a wide-band linear array probe (5.0–13.0 MHz). This method for measuring tendon thickness has previously been described and used for midportion.^16,42 All participants were lying prone with hip and knee in full extension and the ankle hanging outside the treatment bed. Three US images were obtained, and tendon thickness was measured at the thickest part of the tendon for both injury locations (midportion and insertional). To determine the degree of tendon thickening within a tendon, a second measurement for tendon thickness on the injured side was obtained at 2 cm proximal to the calcaneal notch in participants with midportion Achilles tendinopathy and at the distal soleus muscle in participants with insertional Achilles tendinopathy (Fig. 1). These 2 locations were chosen because they often have no tendon pathology. The 3 measurements were averaged and used for quantifying the degree of tendon thickening as following: (tendon thickening = thickness at the thickest portion – thickness in the area without pathology).

Figure 1.

Ultrasound imaging of Achilles tendinopathy. (Top) Midportion tendinopathy. (Bottom) Insertional tendinopathy. The lines represent thickness measurements. Line a represents the thickest portion of tendinopathy. Line b represents normal tendon thickness (location for midportion 2 cm away from insertion; location for insertional at end of soleus muscle). The arrow represents soleus muscle ending.

Viscosity and Shear Modulus

Continuous shear wave elastography⁴³ quantified the viscoelastic properties of participants’ Achilles tendons. This noninvasive technique is valid and reliable to estimate Achilles tendon viscoelastic properties and was previously described.^13,43,44 In brief, all participants were evaluated in prone position. The participant’s hip and knee were placed in the extension position, and the foot position was fixed at 10 degrees of dorsiflexion. An external actuator was placed close to an ultrasound transducer to propagate a shear wave along the length of the tendon. A series of ultrasound images were acquired at the injured location and analyzed to calculate static shear modulus and viscosity using custom code on MATLAB (The MathWorks, Inc, Natick, MA, USA) software.^43,45 Three trials were averaged and used for data analysis. For each outcome (shear modulus and viscosity), we calculated the limb symmetry index (LSI) by dividing the outcome for the most symptomatic side by the outcome for the least symptomatic side and multiplying by 100. The use of the LSI enabled us to compare the groups over time.

Calf Muscle Endurance

Calf muscle endurance was measured for each side by a single leg heel-rise test using a linear encoder (MuscleLab Measurement System; Ergotest Innovation, Porsgrunn, Norway).^7,46 Participants were asked to stand on 1 leg on a 10-degree inclined box and perform heel rises at a cadence of 1 repetition every 2 seconds until fatigue. The linear encoder was taped on the participant’s heel and was used to calculate the total work performed in joules (total work = total linear displacement × body weight). We calculated the LSI by dividing the total work on the most symptomatic side by the total work on the least symptomatic side multiplying by 100. The use of the LSI enabled us to compare the groups over time. Any individual who reported a new problem at the uninvolved side during the study was excluded from the calf muscle endurance analysis over time.

Study data were collected and managed using the Research Electronic Data Capture tool, which is a secure, web-based software platform designed to support data capture for research studies.^47,48

Statistical Analysis

Descriptive statistics for demographics, injury characteristics, and all outcome variables at baseline are reported. When the data were not normally distributed, median, and interquartile range (IQR) were reported, and parametric and nonparametric tests were used accordingly. LSIs (as percentages) (ie, [more symptomatic/less symptomatic] × 100) were calculated for viscoelastic properties and heel-rise test outcomes for normalized comparison among groups.

At baseline, group comparisons were analyzed by using 1-way analysis of variance or Kruskal-Wallis tests with post hoc comparisons performed with Tukey honestly significant difference and Games-Howell post hoc tests, respectively. In addition, Fisher exact tests were used for comparison among groups for sex, injury location, and unilateral/bilateral injury.

For longitudinal comparison, a linear mixed model was used to analyze differences over time, the average between-groups difference, and the interaction between group and time. We used BMI as a covariate in the analysis because there was a significant difference in BMI among the groups and BMI has been found to be a potential confounding variable of tendinopathy because higher BMI correlated to Achilles tendinopathy⁴⁹ and negatively affected tendon structure.⁵⁰ When normality assumption was violated for this analysis, data transformations were employed when the assumption was not satisfied. Lastly, we described the change in level of fear of movement for each group over time using means and SEs. All statistical analysis was completed using IBM SPSS statistics software version 26 (IBM, Armonk, NY, USA), and a P value of less than .05 was considered significant.

Role of the Funding Source

The funding source had no role in the study’s design, conduct, and reporting.

Results

In this secondary analysis of the large cohort study, a total of 59 participants with Achilles tendinopathy fit the inclusion criteria and were divided into 3 groups based on the baseline TSK score (see Suppl. Figure). Characteristics of participants and their outcomes at baseline are presented in Tables 1 and 2.

Table 1.

Demographics and Injury Characteristics^a

Characteristic	Patients With Low TSK Scores (≤33) (n = 16)	Patients With Medium TSK Scores (34–41) (n = 28)	Patients With High TSK Scores (≥42) (n = 15)	P
Age, y, mean (SD)	51.9 (15.3)	52.7 (15.2)	61.1 (11.1)	.137
BMI, kg/cm2				.021b
Median (Q1–Q3)	24.3 (22.3–25.4)	26.4 (22.5–30.8)	28.1 (25.2–33.6)
Mean (SD)	24 (3.2)	27.7 (7.5)	30.4 (8.1)
Height, cm, mean (SD)	174.8 (10.7)	175 (12.1)	170.5 (10.9)	.444
Weight, kg, mean (SD)	74.4 (14.7)	84.5 (21.9)	88 (24)	.165
Symptom duration, mo, median (Q1–Q3)	4.2 (2.6–12.7)c	12.5 (4.4–24.8)	12.1 (7.3–28.3)	.059
Sex, no. of men/women	8/8	15/13	7/8	.908
Injury location (insertional/midportion/both), no. of patients	2/10/4	12/12/4	5/7/3	.355
Unilateral/bilateral, no. of patients	14/2	23/5	14/1	.587
Previous injury (none/MSK injury/medical problem), no. of patients	9/3/4	22/3/3	12/1/2	.560

^a Nonparametric tests were performed when the median and interquartile range (IQR) (first quartile [Q1]–third quartile [Q3]) or frequency was reported. BMI = body mass index; MSK = musculoskeletal; TSK = Tampa Scale for Kinesiophobia.

^b A pair comparison revealed that only patients with high TSK scores had a significantly greater BMI than patients with low TSK scores (P = .003).

^c n = 15.

Table 2.

Results at Baseline for Patient-Reported Outcome Measures, Tendon Structure, and Calf Muscle Endurance (N = 59)^a

Patient-Reported   Outcome Measure	Patients With Low TSK Scores (≤33) (n = 16)	Patients With Medium TSK Scores (34–41) (n = 28)	Patients With High TSK Scores (≥42) (n = 15)	1-Way ANOVA P Value	Effect Size (η 2 )
VISA-A	68.1 (21)	49.1 (21.5)	43.1 (26)	.007b	0.163
PAS current, median (IQR)	5 (4–6)	4 (3–4)	3 (3–5)	.06	0.066
PAS preinjury, median (IQR)	5 (4–6)	5.5 (4–6)	4 (3–5)	.127	0.07
FAOS-QOL	64.5 (19.5)	44.2 (13.5)	40.4 (19.9)	<.001	0.257
Tendon structure
Thickening, mmc	2.2 (2.1)	2.8 (2.2)	2.8 (2.4)	.671	0.022
Shear modulus, kPa	99.92 (19.1)	96.2 (18.4)	102.1 (14.3)	.624	0.021
Shear modulus, LSI, %	102.4 (23.6)	109.9 (26.7)	103.1 (22.5)	.609	0.022
Viscosity, Pa*s	0.05221 (0.007)	0.05058 (0.016)	0.04970 (0.0148)	.886	0.005
Viscosity, LSI, %	92.4 (18.3)	94.8 (32.7)	88.5 (31.7)	.824	0.009
Calf muscle endurance
Heel-rise work, LSI, %	82.1 (38.2)	68.9 (46)	43.6 (50.3)	.068	0.098

^a Values are reported as mean (SD) unless otherwise indicated. Kruskal-Wallis tests were performed when the median and interquartile range (IQR) were reported. ANOVA = analysis of variance; FAOS-QOL = quality-of-life subscale of the Foot and Ankle Outcome Score; LSI = limb symmetry index; PAS = Physical Activity Scale; Pa*s = viscosity unite (Pascal seconds).

^b A pair comparison showed that patients with low TSK scores had significantly lower symptom severity (Victorian Institute of Sports Assessment–Achilles [VISA-A]) and higher quality of life (FAOS-QOL) at baseline than patients with medium (P = .02 and .018, respectively) and high (P = .003 and .006, respectively) TSK scores.

^c n = 58.

BMI was the only significantly different measure among groups (P = .021, ε² = 0.13). The high TSK group (median =  28.1, IQR = 25.2–33.6) had significantly greater BMI than the low TSK group (median = 24.3, IQR = 22.3–25.4) (P = .003). The medium TSK group (median = 26.4, IQR = 22.5–30.8) was not significantly different from either the low or the high TSK group (P > .05).

Outcomes Differences at Baseline

Participant-Reported Outcome Measure

There was a significant difference in VISA-A scores among groups (P = .007, partial eta squared [η_p²] = 0.163). The low TSK group had significantly lower symptom severity than both the medium and the high TSK groups (P = .02 and .018, respectively), which did not differ from each other (P > .05) (Tab. 2). FAOS-QOL scores were also significantly different among the groups with a large effect size (P < .001, η_p² = 0.257). Participants in the low TSK group had higher FAOS-QOL scores than those in the medium and high TSK groups (P = .003 and .006, respectively), but there was no significant difference between the medium and high TSK groups (P > .05). The physical activity levels at baseline were not significantly different among the groups but with a medium effect size (P = .06, η_p² = 0.066).

Tendon Thickening, Viscoelastic Properties, and Calf Muscle Endurance

There were no significant differences (P = .609–.824, η_p² =  0.009–0.022) among groups at baseline for tendon thickening, shear modulus, and viscosity (Tab. 2). There were no significant differences among groups at baseline for tendon thickening (P = .671, η_p² = 0.022), shear modulus (P = .609, η_p² = 0.022), viscosity (P = .824, η_p² = 0.009), or heel rise (P = .068, η_p² = 0.098).

Outcome Differences Over Time

The results of all outcomes below were based on 59 participants except for tendon thickening and LSI of heel-rise total work (n = 58) due to missing data for 1 participant for tendon thickening and 1 developed a new problem on the uninvolved side excluding the heel-rise test for 1 participant.

After adjusting for baseline BMI, groups did not significantly differ in change over time for any outcome (VISA-A, FAOS-QOL, PAS, thickening, shear, viscosity, or heel-rise work; all Ps > .05) (Suppl. Tab. 1 and Tab. 2). There was a significant main effect of time averaged across groups for VISA-A (F_2,89.920 = 26.290, P < .001), FAOS-QOL (F_2,85.391 = 24.249, P < .001), PAS (F_2,83.840 = 4.966, P = .009), and heel-rise work (F_2,85.481 = 9.08, P < .001). All of these outcomes improved over time (Figs. 2 and 3). There was no significant change in tendon thickening, shear modulus, or viscosity (all Ps > .05).

Figure 2.

Symptom severity (Victorian Institute of Sports Assessment–Achilles [VISA-A]) (A), quality of life (quality-of-life subscale of the Foot and Ankle Outcome Score [FAOS-QOL]) (B), and physical activity level (Physical Activity Scale [PAS]) (C) at baseline, 6 months, and 12 months (n = 59). All outcomes improved over time. P values were < .001, <.001, and .009, respective to symptom severity, quality of life and physical activity level, with no interaction effects among groups. Adjusted means (SEs) for body mass index (BMI). P_time = difference over time; P_{group × time} = interaction between group and time.

Figure 3.

(A–D) Outcomes of viscoelastic properties (LSI and absolute values). (E) Tendon thickening for each group (n = 59 and n = 58, respective to viscoelastic properties outcomes and tendon thickening). There were no significant differences over time or interaction effects for viscoelastic properties and tendon thickening among groups (P > .05). Adjusted means (SEs) for body mass index (BMI). (F) Limb symmetrical index of heel-rise work improved over time for each group (n = 58) (P < .001), with no interaction effects among groups. Adjusted means (SEs) for BMI. P_time = difference over time; P_{group × time} = interaction between group and time.

Change in Kinesiophobia Over Time

There was a significant interaction between groups and time on TSK score (F_4,112 = 4.833, P = .001, η_p² = 0.147). The simple main effect of time was examined for each group. The high and medium TSK groups saw a significant decrease in kinesiophobia across time (high: F_2,55 = 15.117, P < .001, η_p² = 0.355; medium: F_2,55 = 10.027, P < .001, η_p² = 0.267), but the low TSK group did not (F_2,55 = 0.868, P = .426, η_p² = 0.03). The high and medium TSK groups showed a reduction in TSK scores after 6 months and remained unchanged from 6 to 12 months, with no change for the low TSK group throughout the study (Fig. 4).

Figure 4.

Means and SDs for level of kinesiophobia changes for each group over time (n = 59).

Discussion

The primary goal of this study was to investigate if there were differences in characteristics and injury severity at baseline and in recovery over time between participants with Achilles tendinopathy and different levels of kinesiophobia (low, medium, and high TSK). We found differences among the groups at baseline for BMI of participants and outcome measures of symptom severity and quality of life. The high TSK group had significantly greater BMI and symptom severity and lower quality of life at baseline. On the other hand, we observed that all groups improved over time, with no differential effects in regard to recovery of symptoms, quality of life, physical activity level, and calf muscle function. However, none of the groups improved significantly in tendon morphology and viscoelastic property outcomes after 1 year. Despite the finding that high TSK group showed the highest BMI and the worse symptom severity as well as QOL at baseline, it improved similarly to the other groups over the 12 months in all the outcome domains. While the TSK scores in high and medium TSK groups decreased after 6 months, it was only the high TSK group that had a shift large enough to change from 1 subgroup (high TSK) to another (medium TSK).

Outcomes Differences at Baseline

At baseline, there were no participant characteristic differences among the groups except BMI, which was greater in the high TSK group than in the low TSK group but not the medium TSK group. This finding is in agreement with previous studies because high BMI was observed in participants with high fear of movement who had low back pain or total knee arthroplasty.^51,52 Elevation of BMI increases the chances of musculoskeletal injuries, including Achilles tendinopathy.^49,53–56 However, BMI has not been found to play a role in determining participants with chronic musculoskeletal pain who are likely to respond to conservative treatment.⁵³ We also found that physical activity level in the high TSK group was the lowest among the groups with a medium effect size even though the difference was not statistically significant. One possible explanation for BMI variations between the groups could be that participants in the high TSK group may have gained weight due to limiting and decreasing their physical activity level after developing symptoms. However, the role of changing the physical activity level in the development of obesity remains unclear, and we cannot draw any conclusion about the relationship in our study.^57,58 Increased body weight and BMI has indirect influences on tendon structure abnormality because it causes excessive mechanical loading and changes tendon metabolic function.^59,60 Further studies are needed to examine the impact and mechanisms of obesity on tendon structures.

The participant-reported outcome measures at baseline indicated that the participants in the medium and high TSK groups had greater disability than the low TSK group. The participants with high TSK showed inferior scores compared with participants with medium TSK in the symptom severity and quality of life outcomes. In a cross-sectional study, a similar result was found when comparing pain and disability in participants with anterior knee pain with high and low fear of movement.⁶¹ A previous systematic review reported that a greater degree of kinesiophobia was associated with greater pain and disability as well as lower QOL in participants with chronic musculoskeletal pain.⁶² Although our data did not exhibit significant differences for calf muscle function among groups, a medium effect size was detected (η_p² = 0.098). In fact, missing 4 participants at the baseline assessment may have reduced the statistical power.

Outcome Differences Over Time

All groups improved significantly in their symptoms, physical activity levels, QOL, and calf muscle function over time but with no change in tendon viscoelastic property outcomes. Contrary to our hypothesis, we did not see differences among groups at 6 and 12 months for all outcomes. We found the group with a high level of fear recovered to the same degree as other groups. All the groups had a slight reduction in tendon thickening, with the high TSK group having the largest reduction of tendon thickening among the groups, but it was not significant over time. It is hard to conclude that this reduction in tendon thickening may be an indication of tendon adaptation in response to increasing physical activity level or “tendon mechanical loading” in the past 6 months in the high TSK group.⁶³ We also should remember that the high and medium TSK groups had greater BMI, and a slight increase in physical activity level may increase the load on the tendons to a greater degree. It is likely when high-intensity loading is performed, this may create enough stimulation of the mechanoreceptors that increase synthesis and protein turnover and remolding of the tendon.⁶⁴ Kinesiophobia in individuals with Achilles tendinopathy may lead to inadequate loading. The current study also observed that participants’ physical activity increased in conjunction with decreased fear of movement at 6 months. Thus, further research is needed to understand the association between tendon loading and fear of movement. Although participants in this study did not receive treatment, it is feasible that they benefited indirectly from learning about the injury when participating.

TSK Level Change for Each Group and Rate of Recovery

The level of kinesiophobia in the high TSK group decreased over time, resulting in the high and medium TSK group having similar levels of kinesiophobia at 6 months. The mean change was 6 points, which suggests that the high TSK group had a clinically meaningful improvement based on previously reported minimal clinically important difference of TSK.⁶⁵ It is possible that taking part in the study and receiving information about the injury could have been beneficial for the high TSK group and resulted in decreased fear of movement. On the other hand, it could also be expected that these participants improved for other reasons because receiving other treatments was not an exclusion criterion for this observational study. However, we propose that further evaluating how participant education might benefit those with high kinesiophobia and Achilles tendinopathy is of interest.

The strength of this study was that we evaluated all the domains of the injury during the recovery of Achilles tendinopathy over time. However, there are limitations to this study. The sample size was small and not equal in each group, which can possibly reduce the statistical power of the study and lead to bias; therefore, further research should include a larger sample. The attrition rate of 46% (56/121) due to the specific inclusion and exclusion criteria is a limitation; however, there were no significant differences in baseline characteristics between the participants included and excluded from this study (Suppl. Tab. 3). Another limitation is heterogeneity within the Achilles tendinopathy cohort. Our sample included (96%) Whites, which is relative to the normal population. Therefore, it can mainly be generalizable to similar participant characteristics.

This study compared outcomes at baseline and recovery over time for participants with Achilles tendinopathy who had different levels of kinesiophobia. Our main finding showed that, at baseline, the low TSK group had lower symptom severity and higher QOL than the medium and high TSK groups. Without controlling for interventions, all groups improved over time irrespective of levels of kinesiophobia at baseline. In addition, adjusting outcomes for BMI did not reveal differences among groups over time. Our secondary results exhibited that participants’ fear in the high and medium TSK groups decreased at 6 months, but the mean TSK scores remained the same in the low TSK groups. The improvement in the level of kinesiophobia in the high and medium TSK groups during the first 6 months may be the reason for lack of difference in recovery. All the participants in the study received information about the injury at baseline, and some went on to receive treatment for their injury, which might have helped reduce the participants’ level of kinesiophobia. Further evidence is needed to determine the reason for change in kinesiophobia over time and how it might affect treatment outcomes in individuals with Achilles tendinopathy.

Author Contributions

Concept/idea/research design: N. Alghamdi, R. Pohlig, M. Lundberg, K. Silbernagel

Writing: N. Alghamdi, R. Pohlig, M. Lundberg, K. Silbernagel

Data collection: N. Alghamdi, K. Silbernagel

Data analysis: N. Alghamdi, R. Pohlig, M. Lundberg, K. Silbernagel

Project management: K. Silbernagel

Consultation (including review of manuscript before submitting): M. Lundberg

Funding

Research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Numbers R01AR072034 and R21AR067390. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Disclosures

The authors completed the ICMJE Form for Disclosure of Potential Conflicts of Interest and reported no conflicts of interest.