The myth of muscle balance. A study of relative strengths and excursions of normal muscles about the foot and ankle

TLDR

The study measured muscle fibre lengths and weights in five cadaveric lower limbs to compute each muscle’s relative strength and excursion. The results show that ankle plantarflexors are six times stronger than dorsiflexors, refuting the muscle‑balance concept in tendon transfer surgery and suggesting task‑appropriateness as a guide; the fixed link between fibre length and excursion explains why contractures reduce movement range, and tendon lengthening corrects deformity but does not restore active range.

Abstract

The lower limbs of five cadavers were dissected and the lengths of the muscle fibres and the weights of all the muscles below the knee were measured. From this information the relative strength and excursion of each muscle was determined. We found that the plantarflexors of the ankle were six times as strong as the dorsiflexors. We have therefore discarded the concept of "muscle balance" in tendon transfer surgery and propose that task appropriateness should be the guide. The constant relationship between muscle fibre length and muscle excursion means that contractures are accompanied by decreased excursion. Tendon lengthening improves deformity but does not improve the decreased active range of movement.