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

Key points

1. 01Symptomatic limbs had a smaller flexor hallucis longus cross-sectional area and a thinner soleus, but a thicker lateral gastrocnemius, than control limbs.
2. 02Overall lean lower leg girth did not differ between groups, suggesting smaller muscles were masked by a thicker lateral gastrocnemius.
3. 03Strength was significantly lower in the flexor hallucis longus, soleus, peroneal and tibialis anterior muscles of symptomatic limbs.
4. 04Symptomatic runners completed about 56 percent fewer single-leg heel raises, indicating markedly reduced calf endurance.
5. 05Authors suggest rehabilitation should target strengthening of the flexor hallucis longus, soleus, tibialis anterior and peroneal muscles plus calf endurance.

How it was conducted

Design

Case-control study (cross-sectional) of active long-distance runners

Participants

11 runners with MTSS matched to 11 asymptomatic controls, drawn from a larger cohort of 64 runners

Limbs analysed

20 MTSS symptomatic limbs vs 20 control limbs (9 of 11 cases had bilateral symptoms)

Measures

Ultrasound muscle thickness and cross-sectional area, lean lower leg girth, hand-held dynamometer strength, single-leg heel raise endurance

Analysis

Mixed-model linear regression (p < 0.05), Cohen's d effect sizes

What they found

• Flexor hallucis longus cross-sectional area was smaller in symptomatic limbs (481.9 mm2 vs 538.6 mm2; mean difference 56.7; Cohen's d 0.46; p = 0.042).
• Soleus thickness was smaller in symptomatic limbs (16.5 mm vs 18.4 mm; mean difference 1.9; Cohen's d 0.65; p = 0.016).
• Lateral gastrocnemius thickness was larger in symptomatic limbs (15.8 mm vs 13.9 mm; mean difference -1.9; Cohen's d -0.95; p = 0.007).
• Lean lower leg girth did not differ (0.94 vs 0.95; Cohen's d 0.01; p = 0.813).
• Flexor hallucis longus strength was lower in symptomatic limbs (20.3 vs 27 % BW; mean difference 6.7; Cohen's d 0.75; p = 0.023).
• Peroneal strength was lower (27.9 vs 33.5 % BW; mean difference 5.6; Cohen's d 0.81; p = 0.010).
• Soleus strength was lower (63.7 vs 72.7 % BW; mean difference 9; Cohen's d 0.61; p = 0.035).
• Tibialis anterior strength was lower (33.5 vs 42 % BW; mean difference 8.5; Cohen's d 0.83; p = 0.005).
• Ankle plantar flexor endurance was lower (33.2 vs 75.4 heel raise repetitions; mean difference 42.2; Cohen's d 0.80; p = 0.005), about 56 percent fewer heel raises.

Limitations

• Cross-sectional design cannot establish whether the muscle differences cause or result from MTSS.
• Very small sample (11 cases and 11 controls) limits definitive conclusions.
• Tibialis posterior, a muscle relevant to tibial bending, could not be assessed due to ultrasound probe constraints.
• Lower strength could partly reflect pain-related neuromuscular adaptation rather than a primary cause.

Why it matters

For patients

If you run with shin splints, weak and less enduring calf and foot muscles may be part of the problem, so targeted strengthening may help recovery.

For clinicians

Rehabilitation for MTSS runners should target strengthening of the flexor hallucis longus, soleus, tibialis anterior and peroneal muscles plus calf endurance capacity.

For readers

This small study links specific lower leg muscle deficits to shin splints but cannot yet prove cause, so prospective studies are needed.