CORP: In vivo muscle strength-perspectives on the design and interpretation of preclinical animal studies.

Accurate and reproducible tools to evaluate skeletal muscle contractility help to advance the field of physiology by defining skeletal muscle function in the context of skeletal muscle development, disease, aging, and injury recovery. The biomechanical assessment of muscle strength can be accomplished by measuring in vivo muscle torque, specifically, the muscle force generated at a moment arm around a joint. This approach to assess skeletal muscle contractility in preclinical animal studies primarily measures muscle torque in anesthetized animals using noninvasive electrophysiological stimulation. This method is advantageous because skeletal muscle contractions are evoked in a controlled, quantifiable manner that is independent of subject motivation, allowing for maximal functional data and reproducible research outcomes. The purpose of this Cores of Reproducibility in Physiology (CORP) review is to discuss the underlying physiology of the in vivo method, to highlight common outcomes and their physiological importance, and to provide considerations for technical reproducibility and data interpretation. The hope is this CORP will provide skeletal muscle researchers with the foundational and practical knowledge to better incorporate the in vivo technique in their future studies.