In vivo measurement of hindlimb neuromuscular function in mice.

INTRODUCTION: In vitro or in situ methods to assess neuromuscular performance in rodents are invasive and inadequate to fully assess large hindlimb muscles. METHODS: An in vivo hindlimb exertion force test (HEFT) was developed to quantify muscle function peak force (PF), peak rate of force development (PRFD), and short- and long-latency reaction times (SLRT and LLRT, respectively) in C57BL/6J mice. RESULTS: PF did not change with one- and three-times-per-week repeated HEFT trials, demonstrating assessment reproducibility. However, PRFD decreased with trial, indicating that mice modified response behavior while achieving the same PF. Separately, mice were subjected to 14 days of hindlimb suspension (HS) to induce muscle atrophy. Concomitant with decreased lean carcass and individual muscle masses, HS mice showed reduced PF and LLRT. CONCLUSIONS: The results demonstrate that HEFT is an effective tool for evaluating in vivo hindlimb neuromuscular performance due to disuse muscle atrophy and potentially for other disease and injury models.