Examining Relationships and Differences Between the Gastrocnemius and Soleus of the Affected and Healthy Lower Limb of Athletes with Medial Tibial Stress Syndrome

Objectives: Medial tibial stress syndrome (MTSS) is a common overuse injury among athletes, yet limited evidence exists regarding muscle-specific deficits. This study aimed to (a) examine differences in gastrocnemius and soleus strength and endurance between the affected and healthy lower limb, and (b) investigate the relationships between gastrocnemius and soleus strength, endurance, and pain intensity in athletes with MTSS. Methods: Thirty athletes aged 18–40 years with MRI-confirmed MTSS, who had completed a standardized physiotherapy program, underwent isometric dynamometry and heel-rise endurance testing under knee-extended (gastrocnemius) and knee-flexed (soleus) conditions. Relative strength values and heel-rise repetitions were compared between limbs using paired t-tests. Correlations and regression analyses were performed between pain intensity, strength, and endurance of the affected limb using Pearson’s r and simple linear regression. Results: Significant deficits were found in both muscles of the affected limb, with reduced isometric strength and fewer heel-rise repetitions (gastrocnemius heel-rise: t(29) = −6.47, p < 0.001; gastrocnemius strength: t(29) = −6.27, p < 0.001; soleus heel-rise: t(29) = −5.37, p < 0.001; soleus strength: t(29) = −4.87, p < 0.001). Strong positive correlations were observed between muscle strength and endurance, while higher pain intensity was negatively associated with gastrocnemius performance. Moreover, pain intensity significantly predicted gastrocnemius strength (F(1,28) = 5.90, p = 0.022, R2 = 0.17) and endurance (F(1,28) = 7.56, p = 0.009, R2 = 0.22), but not soleus function. Physiotherapy duration, number of physiotherapy sessions, and self-reported pain improvement were not significant predictors to either soleus or gastrocnemius endurance, only training frequency emerging as the only independent variable. Conclusions: Athletes with MTSS exhibited notable impairments in plantarflexor function. These findings underscore the importance of targeted strength and endurance interventions for both the gastrocnemius and soleus muscles to optimize recovery, enhance load tolerance, and reduce recurrence risk. Future research should include pre- and post-rehabilitation assessments, larger sample sizes, and sport-specific cohorts.