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Marco Hagen, Daniel Sanchez-Bergmann, Sebastian Seidel, Matthias Helmut Lahner

• \(\bf Background:\) The angle-dependent torque capacity of the subtalar pronators and supinators is important to maintain dynamic ankle stabilisation. Based on the peak torques during maximum voluntary isometric pronation and supination across the subtalar range of motion, the strength curves of younger and elderly males and females were investigated. \(\bf Methods:\) Maximum voluntary isometric subtalar pronator and supinator strength tests were administered to 30 younger and 30 elderly volunteers (each 15 male and 15 female subjects). Total active subtalar ranges of motion and peak pronator and supinator torques were measured in five anatomical subtalar joint angles using a custom-built apparatus with two force transducers. Furthermore, relative torques (normalised to the individual peak torque) and pronator-to-supinator strength-ratios were also calculated. \(\bf Results:\) Pronator-to-supinator strength ratio, and peak pronator and supinator torques are affected by age and by joint angle x age interactions. All supinator strength curves show a steadily descending characteristic from the pronated to the supinated positions. The pronator strength curve had an inverted U-shaped characteristic, except for younger women of whom 47 % exert highest peak values in the end-range pronation angle. Both relative pronator and supinator strength are dependent on sex (\(\it P\) < 0.05). Relative pronator strength is also affected by joint angle x sex (\(\it P\) < 0.0001) and joint angle x sex x age (\(\it P\) < 0.05) interactions. Beside age effects on all range of motion parameters, pronation range of motion is influenced by a sex x age interaction (\(\it P\) <0.05). \(\bf Conclusions:\) Age- and sex-related differences in both subtalar strength profile and range of motion have to be considered when testing strength across subtalar range of motion. Younger females have higher pronator strength capacity in the most pronated joint angle, which may be due in part to their greater subtalar joint range of motion compared to the other groups. In the most supinated position both pronator and supinator strength capacity is reduced in younger females compared to younger males.