Denis Holzer1*, Florian Kurt Paternoster1, Daniel Hahn2,3, Tobias Siebert4, Wolfgang Seiberl1,5*
1Technical University of Munich, Department of Sport and Health Sciences, Biomechanics in Sports, Munich, Germany
2Ruhr University Bochum, Faculty of Sport Science, Human Movement Science, Bochum, Germany
3University of Queensland, School of Human Movement and Nutrition Sciences, Brisbane, Australia
4University of Stuttgart, Department of Motion and Exercise Science, Stuttgart, Germany
5Bundeswehr University Munich, Department of Human Sciences, Human Movement Science, Neubiberg, Germany
Abstract
Moment arm-angle functions (MA-a-functions) are commonly used to estimate in vivo muscle forces in humans. However, different MA-a-functions might not only influence the magnitude of the estimated muscle forces but also change the shape of the muscle’s estimated force-angle relationship (F-a-r). Therefore, we investigated the influence of different literature based Achilles tendon MA-a-functions on the triceps surae muscle-tendon unit F-a-r.
The individual in vivo triceps torque-angle relationship was determined in 14 participants performing maximum voluntary fixed-end plantarflexion contractions from 18.3±3.2° plantarflexion to 24.2±5.1° dorsiflexion on a dynamometer. The resulting F-a-r were calculated using 15 literature-based in vivo Achilles tendon MA-a-functions.
MA-a-functions affected the F-a-r shape and magnitude of estimated peak active triceps muscle-tendon unit force. Depending on the MA-a-function used, the triceps was solely operating on the ascending limb (n=2), on the ascending limb and plateau region (n=12), or on the ascending limb, plateau region and descending limb of the F-a-r (n=1).
According to our findings, the estimated triceps muscle-tendon unit forces and the shape of the F-a-r are highly dependent on the MA-a-function used. As these functions are affected by many variables, we recommend using individual Achilles tendon MA-a-functions, ideally accounting for contraction intensity-related changes in moment arm magnitude.