A pilot investigation of muscle activation patterns in individuals with exercise-related leg pain compared to uninjured individuals

Exercise-related leg pain (ERLP) comprises between 9% and 32% of lower limb injuries. A recent prospective study of female college athletes showed 76% of participants had a history of ERLP with strong association to recurrence. Preliminary research has identified increased pronation as a risk factor in development of ERLP and others have shown that a pronated foot posture is associated with altered muscle function. Given that specific alterations in neuromuscular control have been demonstrated with other musculoskeletal conditions such as quadriceps impairments in patello-femoral pain and trunk muscles in low back pain, we hypothesised that there would be altered muscle function of the lower limb with ERLP. Methods: A pilot study was conducted to determine sample size requirements to evaluate the hypothesis. We measured electromyographic (EMG) activity during gait from 12 uninjured individuals and 7 individuals with a history of ERLP intramuscular EMG recordings from tibialis posterior and surface EMG recordings from tibialis anterior, soleus, peroneus longus, medial and lateral gastrocnemius, posterior gluteus medius, and knee flexors and extensors were performed. A multivariate ANOVA was conducted to determine effect sizes for differences between the uninjured and ERLP groups and to facilitate sample size estimates to be calculated for effect sizes larger than 0.8. Results and conclusion: Effect sizes for mean differences in peak and average activation were 1.2 and 1.1 for tibialis posterior and 0.9 and 1.0 for lateral gastrocnemius. All other muscles displayed effect sizes less than 0.8. For tibialis posterior and lateral gastrocnemius, peak activation was reduced by 19.8% (95% CI: −43.1% to 3.5%) and 26.7% (−60.2% to 6.9%) and average activation by 7.9% (−17.8% to 2.0%) and 13.1% (−28.4% to 2.1%). We recommend further research to be conducted on a larger cohort to confirm these observed differences.