A protocol to prospectively assess risk factors for medial tibial stress syndrome in distance runners

Do Plantar-Flexor Muscle Structure and Function Contribute to Medial Tibial Stress Syndrome in Long-Distance Runners? A Case Report

Two long-distance runners developed medial tibial stress syndrome (MTSS; male age = 26.3 years, female age = 47.5 years) after baseline assessment of plantar-flexor muscle structure and function and spatiotemporal running variables. B-mode ultrasound and lean leg girth characterized plantar-flexor muscle structure. Handheld dynamometry and a single-leg heel raise-to-failure protocol characterized plantar-flexor muscle function. Finally, spatiotemporal running variables were determined during a treadmill protocol. The 2 runners who developed MTSS demonstrated less plantar-flexor strength and endurance capacity than published comparative control data and marked variability in muscle structure. Reduced plantar-flexor strength and endurance capacity were thought to contribute to an impaired ability to resist tibial-bending moments during midstance due to earlier muscle fatigue. Earlier muscle fatigue could, in turn, contribute to increased tibial-bending moments and MTSS development. Therefore, assessing plantar-flexor muscle strength and endurance might help to identify athletes at risk of developing MTSS.

Lower leg muscle structure and function are altered in long-distance runners with medial tibial stress syndrome: a case control study

Background

Medial tibial stress syndrome (MTSS) is a common lower leg injury experienced by runners. Although numerous risk factors are reported in the literature, many are non-modifiable and management of the injury remains difficult. Lower leg muscle structure and function are modifiable characteristics that influence tibial loading during foot-ground contact. Therefore, this study aimed to determine whether long-distance runners with MTSS displayed differences in in vivo lower leg muscle structure and function than matched asymptomatic runners.

Methods

Lower leg structure was assessed using ultrasound and a measure of lower leg circumference to quantify muscle cross-sectional area, thickness and lean lower leg girth. Lower leg function was assessed using a hand-held dynamometer to quantify maximal voluntary isometric contraction strength and a single leg heel raise protocol was used to measure ankle plantar flexor endurance. Outcome variables were compared between the limbs of long-distance runners suffering MTSS (n = 20) and matched asymptomatic controls (n = 20). Means, standard deviations, 95 % confidence intervals, mean differences and Cohen’s d values were calculated for each variable for the MTSS symptomatic and control limbs.

Results

MTSS symptomatic limbs displayed a significantly smaller flexor hallucis longus cross-sectional area, a smaller soleus thickness but a larger lateral gastrocnemius thickness than the control limbs. However, there was no statistical difference in lean lower leg girth. Compared to the matched control limbs, MTSS symptomatic limbs displayed deficits in maximal voluntary isometric contraction strength of the flexor hallucis longus, soleus, tibialis anterior and peroneal muscles, and reduced ankle plantar flexor endurance capacity.

Conclusions

Differences in lower leg muscle structure and function likely render MTSS symptomatic individuals less able to withstand the negative tibial bending moment generated during midstance, potentially contributing to the development of MTSS. The clinical implications of these findings suggest that rehabilitation protocols for MTSS symptomatic individuals should aim to improve strength of the flexor hallucis longus, soleus, tibialis anterior and peroneal muscles along with ankle plantar flexor endurance. However, the cross-sectional study design prevents us determining whether between group differences were a cause or effect of MTSS. Therefore, future prospective studies are required to substantiate the study findings.