Impact of Pilates mat-based exercises on knee kinematics during running

Abstract

Introduction:

Core strengthening, balance, and flexibility programs such as Pilates have been advocated to positively impact running mechanics and prevent lower extremity injuries. The purpose of this study was to assess the effects of a 12-week mat-based Pilates exercise program on dynamic knee valgus alignment in runners.

Methods:

Thirty-four novice runners, including young male and female adults performed a running protocol at baseline. The protocol consisted of the participants running on a treadmill at a constant five miles per hour (mph) for 4 min. Post-examination, participants were randomly assigned to a Pilates or control group (n = 16 and n = 18, respectively). A certified Pilates instructor gave the Pilates group a 12-week home-based program. To ensure participants in the Pilates group performed exercises correctly, the Pilates instructor conducted the first session, and provided feedback to each participant. Participants in both groups performed the same running testing protocol every four weeks. Knee valgus was measured as the medial displacement of the knee joint center during the running stance phase. Repeated measures Analysis of Variance (RepANOVA) was calculated at baseline and 4-, 8-, and 12-weeks post examinations to compare knee valgus during running.

Results:

Although a reduction in dynamic knee valgus was observed within the Pilates group, the RepANOVA analysis revealed this change was not statistically significant.

Conclusions:

Pilates mat-based exercises may improve knee valgus after 12 weeks but a larger sample size, longer intervention duration, or a supervised program should be considered for future research to evaluate its effectiveness.

1. Introduction

Pilates is an exercise system practiced by many looking to improve strength and flexibility (Kloubec and Banks 2004). In recent years, Pilates has become a popular mode of exercise in the general public. Pilates was practiced in only ten percent of health clubs in 1997; however, participation steadily increased with over sixty-three percent of health clubs within the United States offering Pilates training sessions merely a decade later (Rogers and Gibson 2009). Psychological and physiological effects attributed to Pilates are enhanced motivation, increased strength, increased flexibility, increased power, improved balance, and better static and dynamic posture (Lange et al., 2000). Both mat-based and equipment-based exercises are training options within the Pilates exercise system. Several studies have revealed Pilates is used as a tool for rehabilitation and to improve specific movements, muscular strength, and endurance (Altan et al., 2009; Bryan and Hawson 2003; Cozen 2000; Donzelli et al., 2006; Levine et al., 2009; Rydeard et al., 2006).

Musculoskeletal injuries are prevalent in running, with as many as 65% of runners reporting overuse running-related injuries annually (van Gent et al., 2007). Overall injury rates in runners range from 7.7 per 1000 h of running in recreational runners to 17.8 in novice runners (Videbaek et al., 2015). The knee complex is implicated as the most common site of injury in runners and knee injuries account for nearly 20% of all running injuries (van Poppel et al., 2014; van Gent et al., 2007; Hryvniak et al., 2014). The proportion of running-related knee injury in runners ranges from 22.5% in cross country runners to 30.6% in novice runners (Kluitenberg et al., 2015). Mechanisms that have been implicated in the development of knee injuries such as patellofemoral pain syndrome (PFPS) include large quadriceps angle and quadriceps muscle strength deficits and their influence on lateral patellar maltracking. PFPS can be caused due to factors proximal and distal to the knee, which can influence knee mechanics (Dierks et al., 2008). According to Dierks et al., (2008), during the stance phase of running, hip abductors’ weakness may contribute to excessive femoral adduction, leading to an excessive knee valgus moment. These alterations to running mechanics, combined with other increased contact pressures to the lateral femoral condyle and lateral facet of the patella, may lead to PFPS (Dierks et al., 2008).

Decreased strength in hip stabilizing muscles, abductors, extensors, and external rotators may influence anterior knee pain, as well as the development of PFPS (Almeida et al., 2015; Stickler et al., 2015). Moreover, research evidence suggests that knee valgus angles and moments are common predictors of injuries to the anterior cruciate ligament (Ford et al., 2003; Hewett et al., 2006) and patellofemoral joint (Powers 2003; Powers et al., 2003). Dynamic knee valgus is defined as a mechanism in which the center of the knee joint moves medially relative to the hip and foot when it is fixed to the ground (Almeida et al., 2015). Several studies have demonstrated that the knee frontal plane projection angle and decreased hip muscle strength are associated with greater anterior knee pain in participants with PFPS (Almeida et al., 2015; Finnoff et al., 2011; Luedke et al., 2015; Stickler et al., 2015; Willy and Davis 2011). Therefore, strengthening hip musculature and core strengthening interventions have been recommended as strategies in treating clients with PFPS and its prevention to reduce pain and improve overall function within the knee complex.

Runners are prone to overuse injury, given the repetitive nature of the activity, along with the unpredictability of changes in movement, including acceleration, deceleration, cutting, pivoting, and changes in stride length and pace, such as those required when ascending and descending inclines. Imbalances and inefficiencies in functional movements are considered contributors to running-related injuries (Laws et al., 2017). Pilates is a dynamic and functional mode of exercise that focuses on motor control from a strong and stable core base (Lange et al., 2000; McNeil 2014). Laws et al., (2017) found that a 6-week course of clinical Pilates significantly improved functional movement in recreational runners and postulated this may reduce the risk of running-related injuries.

In the Pilates method, trunk and hip muscle activation can be obtained in variations of Pilates exercises with alterations of pelvic and trunk posture (Queiroz et al., 2010). Therefore, this study investigated the influence of mat-based Pilates exercises on knee kinematics, specifically knee valgus during running. It was hypothesized that both groups would display knee valgus at baseline when running, and those in the Pilates group would exhibit a reduction in knee valgus throughout the intervention duration compared to the control group.

2. Methods

2.1. Study design and participants

A 12-week randomized controlled trial using a mat-based Pilates core-strengthening exercise program was conducted involving thirty-four young, healthy adults (mean age ± SD: 27.2 ± 0.18 years). Twenty men (mean ± SD; height: 171.77 ± 9.42 cm; weight: 72.59 ± 8.99 kg; BMI: 24.99 ± 2.10 kg/m²) and fourteen women (mean ± SD; height: 158.46 ± 2.96 cm; weight: 53.70 ± 2.45 kg; BMI: 21.81 ± 1.37 kg/m²) completed this study. All participants were over 18 and signed a written informed consent document approved by the Institutional Review Board. All participants were novice college-aged and physically active students that used running several days a week for general health and fitness, or stress management. Inclusion criteria included no history of injury in the preceding six months, no history of lower extremity surgeries, and a generally healthy state. Before involvement in the main trials, each participant’s height, body mass, leg length, pelvis, knee, and ankle width were measured according to the motion analysis software computerized model (Vicon Plugin Gait Model, Vicon Motion Inc., Denver, CO).

2.2. Procedures

Participants reported to the laboratory having refrained from strenuous exercise during the preceding 48 h. A running protocol was conducted four times during this study: at baseline, and at the fourth, eighth, and twelfth weeks. Participants underwent a standardized warm-up session running at four miles per hour (mph) on a treadmill for 5 min before progressively increasing the intensity to five mph without any inclination for another 4 min. To measure dynamic knee valgus during each session, a 3-dimensional high-speed (240 Hz) system (Vicon Motion Inc., Denver, CO) was used during the running protocol, emphasizing the running cycle’s stance phase to measure medial knee displacement. For each participant, 3D kinematics were recorded for the dominant leg throughout the stance phase during the running protocol execution. The dominant leg was defined as the preferred leg to perform a single leg jump (Ortiz et al. 2008, 2011, 2014). Medial knee displacement was defined as the medial trajectory difference traveled by the knee joint center from initial contact to push-off, identified by two footswitches (500Hz; Delsys, Inc, Boston, MA) placed on the plantar aspect of the calcaneus and hallux. Three-dimensional data and pressure from the footswitches were real-time synchronized in the motion analysis software (Vicon Nexus software, Vicon Motion Inc., Denver, CO).

Once baseline measurements were recorded, the participants were randomly assigned to either a home-based Pilates intervention or a control group. The Pilates intervention consisted of a warm-up, seven strengthening exercises (Fig. 1), and a cool-down. The frequency of the program was three times a week, performing each exercise once for 15 repetitions. Participants in the Pilates group performed their first session with a certified Pilates instructor to ensure appropriate technique was performed. The control group was encouraged to continue their daily routine and not engage in additional physical activity or exercise. At the fourth and eighth weeks, the Pilates program’s difficulty level increased by progressing to more challenging exercises (Fig. 1).

Fig. 1.

Progressive Home-Based Pilates Program. Exercise program designed with Physiotec (www.physiotec.ca)

2.3. Data analysis

T-tests were performed at baseline for anthropometrics and valgus variables to ensure both groups were homogenous. A 2 × 4 (group x time) repeated measures ANOVA (RepANOVA) was used to evaluate dynamic knee valgus changes. Group by time interaction and within and between main effects were separately assessed regardless of the interaction being significant based on recommendations by Wei et al., (2012) (Wei et al., 2012). Given the pilot nature of this investigation, an alpha level of p ≥ 0.05 was considered statistically significant for all analyses. SPSS version 26 (IBM SPSS, Armonk, New York) was used for statistical analyses.

3. Results

3.1. Participants

Of the 34 participants initially selected for the study, 31 (men: 20, women: 11) complied with testing and intervention for the entire 12 weeks. Three participants from the Pilates group failed to complete all phases of testing. T-tests showed similarities in anthropometric characteristics and valgus at baseline between groups (Table 1).

Table 1.

Descriptive statistics for anthropometric variables for control and experimental groups at baseline.

Group	n	Weight (kg)* Mean ± SD	Height (cm)† Mean ± SD	BMI (kg/cm2)** Mean ± SD	Valgus (cm)‡ Mean ± SD
Control	18	64.48 ± 10.31	165.86 ± 9.12	23.76 ± 2.42	1.47 ± 0.45
Pilates	13	67.84 ± 13.65	168.70 ± 11.39	23.98 ± 2.49	1.62 ± 0.07
Total	31	66.16 ± 11.98	167.28 ± 10.26	23.87 ± 2.46	1.55 ± 0.26

^*:p = 0.32;

^†:p = 0.14;

^**:p = 0.58;

^‡:p = 0.38.

3.2. Knee valgus

Although dynamic knee valgus improved by 5.1 cm in medial knee displacement in the Pilates group (Table 2), the RepANOVA showed no statistically significant group by time interaction (F(3,31) = 1.36, p = 0.29; β = 0.30) nor between groups differences (F(3.31 = 0.31, p = 0.59; β = 0.08) (Table 2). However, the within-group main effect for both groups combined approached significance (F(3,31) = 2.61, p = 0.059; β = 0.61). Therefore, within time pairwise comparisons were pursued, showing both groups decrease (p = 0.02) in valgus from baseline to the eight-week (Table 2). Individual groups within time pairwise comparisons followed, demonstrating that only the Pilates group improved from baseline to the eight-week (t = 2.40, p = 0.034) testing.

Table 2.

Medial knee displacement (cm) during stance phase throughout time.

Group	Baseline Mean ± SD cm	4-weeks Mean ± SD cm	8-weeks* Mean ± SD cm	12-weeks Mean ± SD cm
Pilates	16.2 ± 0.07	13.6 ± 5.6	11.1 ± 7.3†	12.4 † 6.8
Control	14.7 ± 04.5	14.5 ± 4.1	13.4 ± 5.5	14.5 ± 4.2

SD: standard deviation;

^*statistically significant (p = 0.02) pairwise comparison against baseline measures for both groups combined.

Separate group pre and post pairwise comparison,

^†:p = 0.03.

4. Discussion

This study aimed to determine improvements in dynamic valgus alignment during running during and after a 12- week Pilates mat-based exercise program in young, healthy adults. The study’s initial hypothesis was that the experimental groups’ knee valgus alignment would improve significantly with the addition of a 12-week Pilates program. Our results found that dynamic knee valgus improved with the Pilates intervention, showing a decrease of 5.1 cm in valgus during the running stance phase. However, the magnitude of the between-groups comparison was not statistically significant because of the 1.3 cm improvement on the control group and the large standard deviation during this measurement. Moreover, another possibility for the lack of robust statistically significant differences observed between groups may be data contamination due to the control group modifying their level of exercise and physical activity in a competitive manner or a behavioral change such as initiating an exercise program. This type of behavior in a non-exercise control group has been observed and documented in randomized controlled trials in multiple populations (Waters et al., 2012). Once again, the pre- and post-analysis performed for the two separate groups showed that the Pilates group reduced their knee valgus significantly eight weeks after starting the intervention while the control did not show a statistically significant change. This discrepancy in analyses indicates the possibility of the study being underpowered for this variable (knee valgus).

Weakness in hip muscles leading to dynamic knee valgus can lead to overuse injuries in the lower extremity (i.e., Patellofemoral Pain Syndrome) (Almeida et al., 2015; Finnoff et al., 2011; Luedke et al., 2015; Stickler et al., 2015; Willy and Davis 2011). Carefully evaluating the results of these investigations, it can be hypothesized that a program such as Pilates that strengthens the core and hip stabilizers could be useful in enhancing running mechanics, thus reducing injury risk and other predisposing factors to knee pathologies. Given this investigation used healthy young adults, it is unclear if the improvements of 5.1 cm in knee valgus might be clinically significant in reducing lower body pain and improving running performance in those suffering from knee or hip pathologies. However, the reduction in valgus in our Pilates group shows promise from the intervention in decreasing one of the most documented predisposing factors to knee injuries in exercising populations. Several investigations have reported improvements in lower body pain, strength, and running performance with core strengthening programs, including Pilates, in runners (Drum et al., 2019; Ferber et al., 2015; Finatto et al., 2018; Laws et al., 2017; Lugo-Larcheveque et al., 2006; Munekani and Ellapen 2015).

Finatto et al., (2018) performed a similar investigation in which experienced runners (running > nine months) were divided into an interval training running group and a running group with a 12-week mat-based Pilates program. The Pilates program was divided and progressed in phases like the one used in this investigation. The investigators assessed VO₂, 5K time, metabolic cost, and EMG of core musculature. After the 12-week intervention, the Pilates group exhibited greater VO₂, faster 5k time, lower metabolic cost, and lower EMG activity of the core musculature. The lower core musculature EMG translated into a lower stance phase time and greater forward translation of the body. The authors concluded that greater core musculature strength translated into better core efficiency reducing the stance phase, subsequently creating a faster forward projection of the body and quicker 5k time, lower metabolic cost, and greater oxygen utilization. Placed in context, this agrees with the findings of this investigation of decreased knee valgus as the core musculature, primarily at the hip, has been shown to impact femoral adduction and internal rotation, reducing knee valgus (Powers 2003; Powers et al., 2003). This investigation did not assess stance phase time or oxygen consumption to compare the previous results reported by Finatto et al., (2018). Future investigations evaluating Pilates’ effectiveness on running variables should consider measuring oxygen consumption and temporal-spatial running parameters that translate into functional running outcomes.

The impact of core strength and efficiency during running is evident in Drum et al., (2019), where running economy was assessed during trunk and upper body musculature fatiguing conditions and a control non-fatigue state. The authors found that running economy was impacted negatively during the condition where the trunk and upper body muscles were fatigued. The impact of fatigue in running economy was primarily due to the decrease in forward translation of the body and increased side to side movements of the runner. This is evidence that core musculature decreases movements in the frontal and transverse planes making the body more efficient moving forward in the sagittal plane, improving running economy and running times (Drum et al., 2019). This agrees with this investigation’s findings where the mat-based Pilates program decreased mediolateral knee movements mainly eight weeks after the intervention started.

Similarly, Laws et al., (2017) found statistically significant improvements in hip and knee alignment during functional movement screens in 40 recreational runners after a 6-week Pilates intervention (Laws et al., 2017). These findings are also in agreement with the results of this investigation showing how core musculature strengthened through Pilates can positively improve the knee’s alignment during functional activities. Measurement of and improvements in motor control, biomechanical imbalances, and inefficient functional movements is elusive. Attempts to quantify these measures, such as by using motion analyses equipment and the Functional Movement Screen (FMS), continue to evolve. The FMS likely possesses limited utility in predicting athletic performance, though there exists moderate research support for its efficacy in predicting injury (Finnoff et al., 2011). If the results of our study represent genuine improvements in knee valgus during functional activities and, by extension, injury risk, there are likely contributors related to motor control, and the mitigation of biomechanical imbalances and inefficiencies in functional movements. Exercises geared toward improving core musculature strength likely impact positively these foundational impairments and overall injury risk. From a more global training perspective, for example, in the context of treating the runner with PFPS, a highly prevalent form of running-related knee injury, addressing impairments in mobility and flexibility of the hamstrings is only a part of the equation. Treatment must address impairments in strength, including core musculature, and potentially gait retraining, to effect positive change in any biomechanical imbalances and functional movement inefficiencies which may predominate.

Several limitations impacted the findings of this investigation. Given the pilot nature of this study, we considered reasonable to utilize young, healthy adult participants. However, screening potential participants for abnormal valgus or knee pathologies prior to enrolling in the study may have yielded a more focused participant group versus our healthy participant pool, which may have contributed to a ceiling effect in this study. A home-based intervention program, like the one used in this investigation, could not account for participants’ full participation in the exercises or proper technique of the exercises throughout the 12 weeks. The lack of a higher intensity core exercise protocol created explicitly for running could be an additional weakness for the muscular demands of running. Also, the use of more advanced Pilates equipment such as springs for a higher intensity dose for proximal hip strengthening might be the type of intervention needed for demonstrating functional improvements in running mechanics. A larger sample size might be required to develop a concise relationship between core-strength and knee biomechanical variables and to distinguish a random result versus a real effect. Our results cannot generalize to those runners suffering from PFPS or other related knee pathologies such as Iliotibial band syndrome. A further weakness was not controlling for shoe wear and the influence of the foot on the knee. Therefore, we recommend repeating this investigation in runners suffering from these knee pathologies to determine the effectiveness of this intervention in this population with control of the influences discussed. Finally, a larger sample size and screening participants prior to enrolling in the study for abnormal valgus angles and/or pathology amenable to treatment focusing on reducing medial displacement may mitigate concerns regarding the ceiling effect and its potential impact on the results.

5. Conclusion

In conclusion, our results suggest small improvements in knee valgus during running at 8-weeks of initiating a mat-based Pilates core-strengthening program in young, healthy adults. Our study seems to highlight the impact a program focused on core-strengthening such as Pilates may have on improving knee running mechanics and reducing injury risk.

Practical applications.

Pilates has been advocated to create core stability and control that translates into better, more fluid lower extremity movement. Pilates may help reduce knee valgus during running, increasing motor control at the lumbopelvic-hip complex. This study showed that mat-based Pilates was able to reduce knee valgus by 5.1 cm during running. However, it is unclear the magnitude of such change in the prevention or treatment of knee injuries in runners. The subjects in this investigation exhibited significant variability in knee valgus that suggest the complexity of running mechanics in runners. Individualized attention needs to be paid when evaluating knee valgus in runners to prescribe individualized exercises and prevention strategies for knee pain.