Measurement of instantaneous Achilles tendon moment arm and force during the stance phase of running

Accurate estimates of the Achilles tendon (AT) moment arm (AT(MA)) are necessary for investigating triceps surae muscle-tendon unit loading and function. There are limited reported values of AT(MA) during running. By combining ultrasound and motion capture, AT(MA) was estimated during the stance phase of running. Group mean AT(MA) was estimated at 49.2 +/- 3.8 mm and 37.5 +/- 5.3 mm, relative to the centre of rotation (malleoli markers midpoint) and the ankle finite helical axis respectively. Differences in the corresponding estimated AT forces reached up to 3100 N approximately. Such discrepancies can lead to misinterpretation of the whole muscle-tendon unit function.

Automated summary

Accurate estimates of the Achilles tendon moment arm are crucial for studying the loading and function of the triceps surae muscle-tendon unit. By combining ultrasound and motion capture, the AT moment arm during running was estimated. The differences in the estimated AT forces can significantly affect the interpretation of the muscle-tendon unit function.