Document Type

Journal Article

Publication Title

Biology Open


The Company of Biologists


School of Medical and Health Sciences




Australasian Society for Human Biology and PhD scholarship / Australian Government Research Training Program / Edith Cowan University


Daros Pinto, M., Nosaka, K., Wakeling, J. M., & Blazevich, A. J. (2023). Human in vivo medial gastrocnemius gear during active and passive muscle lengthening: Effect of inconsistent methods and nomenclature on data interpretation. Biology Open, 12(9), article bio060023.


‘Muscle gear’ is calculated as the ratio of fascicle-to-muscle length change, strain, or velocity. Inconsistencies in nomenclature and definitions of gear exist across disciplines partly due to differences in fascicle [curved (Lf) versus linear (Lf,straight)] and muscle [whole-muscle belly (Lb) versus belly segment (Lb,segment)] length calculation methods. We tested whether these differences affect gear magnitude during passive and active muscle lengthening of human medial gastrocnemius of young men (n=13, 26.3±5.0 years) using an isokinetic dynamometer. Lb, Lb,segment, Lf and Lf,straight were measured from motion analysis and ultrasound imaging data. Downshifts in belly gear but not belly segment gear occurred with muscle lengthening only during active lengthening. Muscle gear was unaffected by fascicle length measurement method (P=0.18) but differed when calculated as changes in Lb or Lb,segment (P < 0.01) in a length-dependent manner. Caution is therefore advised for the use and interpretation of different muscle gear calculation methods and nomenclatures in animal and human comparative physiology.



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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.