Angle dependency in strength measurements of the ankle plantar flexors

Summary

Muscle strength (or muscular moment) generated during dynamic contractions varies with joint angle. This raises the question about the choice of a representative angle in the evaluation of strength capacity. To assess this angle dependency in strength measurements, dynamic moment-angle curves for plantar flexor muscles were obtained in 43 healthy subjects (28 men and 15 women) with a controlled acceleration dynamometer at 0.52 rad s⁻¹ (30° s⁻¹) and using maximal static preloading before the beginning of movement to attenuate the force development phase. Differences between gender and correlations between strength and anthropometric measures were calculated at each 0.087 rad (5°). The plantar flexion moment was larger in men, in general, but this difference was largest when the ankle was most dorsiflexed. The correlations between moment and anthropometric measures were also higher in the first half of the plantar flexion movement. These results stress the importance of reporting joint angles at which moment of force measures were made. Furthermore, they show that the maximal strength capacity of the plantar flexors is best represented by the moment measured in dorsiflexion angles when the muscles are lengthened.