Validation of a simplified method for muscle volume assessment.

The present study investigated the validity of a simplified muscle volume assessment that uses only the maximum anatomical cross-sectional area (ACSAmax), the muscle length (LM) and a muscle-specific shape factor for muscle volume calculation (Albracht et al., 2008, J Biomech 41, 2211-2218). The validation on the example of the triceps surae (TS) muscles was conducted in two steps. First LM, ACSAmax, muscle volume and shape factor were calculated from magnet resonance image muscle reconstructions of the soleus (SO), gastrocnemius medialis (GM) and lateralis (GL) of a group of untrained individuals (n=13), endurance (n=9) and strength trained (n=10) athletes. Though there were significant differences in the muscle dimensions, the shape factors were similar across groups and were in average 0.497 ± 0.026, 0.596 ± 0.030, and 0.556 ± 0.041 for the SO, GM and GL respectively. In a second step, the shape factors were applied to an independent recreationally active group (n=21) to compare the muscle volume assessed by the simplified method to the results from whole muscle reconstructions. There were no significant differences between the volumes assessed by the two methods. In conclusion, assessing TS muscle volume on the basis of the reported shape factors is valid across populations and the root mean square differences to whole muscle reconstruction of 7.9%, 4.8% and 8.3% for SO, GM and GL show that the simplified method is sensitive enough to detect changes in muscle volume in the context of degeneration, atrophy or hypertrophy.