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

Key Points

1. Leg muscle structure and function was compared in long-distance runners with and without medial tibial stress syndrome (MTSS).
2. Muscle specific differences in leg muscle size and strength were identified in MTSS symptomatic limbs.
3. This study was cross-sectional and its unknown if differences in muscle size and strength contribute to, and/or are a consequence of, symptoms of MTSS.

BACKGROUND & OBJECTIVE

Medial tibial stress syndrome (MTSS) is one of the most common running-related musculoskeletal injuries with high incidence (9.4%) and prevalence (9.1%) reported in runners (1). Understanding modifiable intrinsic (and extrinsic) factors that may contribute to MTSS symptoms is important for the development of effective prevention and management.

This study aimed to determine whether long-distance runners with MTSS displayed differences in lower leg muscle structure and function compared to matched asymptomatic runners.

Medial tibial stress syndrome has high incidence (9.4%) and prevalence (9.1%) in runners.

Addressing deficits in leg muscle strength and endurance is also likely to be important for runners with MTSS as they progress their training loads.

METHODS

11 runners with MTSS were matched on sex, age, height, body mass, weekly running training distance and limb dominance with 11 asymptomatic (control) runners. Nine participants had bilateral symptoms and so analysis was conducted on 20 symptomatic MTSS limbs and 20 control limbs.

Lower leg muscle structure was quantified by lean lower leg girth and ultrasound image measurement of muscle size (thickness and cross-sectional area) of tibialis anterior, peroneals, soleus, flexor digitorum longus, flexor hallucis longus, and medial and lateral gastrocnemius.

Lower leg muscle function was quantified by maximal voluntary isometric contraction strength of tibialis anterior, peroneals, soleus, flexor digitorum longus, flexor hallucis longus and gastrocnemius using a hand-held dynamometer, as well as ankle plantar flexor endurance capacity using the single leg heel raise test.

RESULTS

• Moderate to large differences (10-14%; Cohen’s d = 0.46 to 0.95) in muscle structure and large differences (12-56%; Cohen’s d = 0.61 to 0.83) in muscle function were identified in MTSS limbs compared to control limbs (see Figure 1).

• Smaller flexor hallucis longus cross-sectional area and soleus thickness, but larger lateral gastrocnemius thickness was observed in MTSS symptomatic limbs.

• Lean lower leg girth did not differ between groups.

• MTSS symptomatic limbs displayed deficits in ankle plantar flexor endurance capacity and maximum voluntary isometric contraction strength of flexor hallucis longus, peroneals, soleus and tibialis anterior.

LIMITATIONS

• Due to the cross-sectional study design, it cannot be determined if differences in muscle structure and function were a contributing factor to, and/or a consequence of, the development of MTSS.

• Small sample size may have limited generalizability and conclusiveness of results.

• Limb data was pooled for analysis (inflating sample size) rather than analysis of people (2).

• Tibialis posterior is an important leg muscle that was not evaluated.

CLINICAL IMPLICATIONS

Differences in leg muscle structure and function were identified in runners with MTSS using reliable methods that are reproducible in the clinical setting. The fact that groups were matched for body characteristics and running distance was a strength of the study compared to previous studies conducted in this area.

Of the leg muscles that were evaluated, the ankle plantar flexors demonstrated the greatest structural and functional changes in runners with MTSS. During running, the ankle plantar flexors provide a positive tibial bending moment in the sagittal plane to counter the peak negative tibial bending moment that occurs at midstance (3,4).

Smaller and weaker ankle plantar flexors, with lower endurance, may compromise the ability to withstand tibial bending moments during running. A smaller and weaker flexor hallucis longus and tibialis anterior may affect attenuation of ground reaction forces and control of the medial longitudinal arch during running, also with implication for tibial strain. Control of the medial longitudinal arch (increased navicular drop and pronation) has been identified as a contributing factor in the development of MTSS (5) and when taken together with the findings of smaller and weaker flexor hallucis longus and tibialis anterior, suggests that strengthening of these muscles could be an important component in prevention and rehabilitation. Addressing deficits in leg muscle strength and endurance is also likely to be important for runners with MTSS as they progress their training loads.

The mechanism(s) underlying differences in leg muscle structure and function in runners with MTSS is not yet known, but we may have some insight soon as further prospective studies appear to be underway in this regard (6).

+STUDY REFERENCE

Mattock J, Steele J, & Mickle K (2021) Lower leg muscle structure and function are altered in long-distance runners with medial tibial stress syndrome: a case control study. Journal of Foot and Ankle Research, 14(1), 1–47.

SUPPORTING REFERENCE

1. Kakouris, N., Yener, N., & Fong, D. T. P. (2021). A systematic review of running-related musculoskeletal injuries in runners. J Sport Health Sci, 10(5), 513-522. doi:10.1016/j.jshs.2021.04.001
2. Menz. (2005). Analysis of paired data in physical therapy research: time to stop double-dipping? The Journal of Orthopaedic and Sports Physical Therapy, 35(8), 477–478. doi.org/10.2519/jospt.2005.0108
3. Scott, S. H., & Winter, D. A. (1990). Internal forces of chronic running injury sites. Med Sci Sports Exerc, 22(3), 357-369. doi:10.1249/00005768-199006000-00013
4. Haris Phuah, A., Schache, A. G., Crossley, K. M., Wrigley, T. V., & Creaby, M. W. (2009). Sagittal plane bending moments acting on the lower leg during running. Gait Posture, 31(2), 218-222. doi:10.1016/j.gaitpost.
5. Newman, P., Witchalls, J., Waddington, G., & Adams, R. (2013). Risk factors associated with medial tibial stress syndrome in runners: a systematic review and meta-analysis. Open Access J Sports Med, 4, 229-241. doi:10.2147/oajsm.s39331
6. Mattock, J., Steele, J. R., & Mickle, K. J. (2018). A protocol to prospectively assess risk factors for medial tibial stress syndrome in distance runners. BMC Sports Sci Med Rehabil, 10, 20. doi:10.1186/s13102-018-0109-1