Characterizing Strain in the Tibia of Rats Exposed to Hindlimb Unloading With an Exercise Countermeasure

Abstract

The purpose of this research was to characterize the strains in the rat tibia induced by controlled muscle contractions of the lower limb. The muscle contractions were generated unilaterally by electrical stimulation of the sciatic nerve in anesthetized animals. The technique was developed by muscle biologists as a way of simulating resistive exercise, and it was used in the current research as a countermeasure for rats undergoing hindlimb unloading to simulate musculoskeletal effects of space flight. The intensity of muscle contraction is quantified by measuring the torque generated at the ankle joint. A wide range of torques can be generated by varying the frequency of the electrical stimulating signal. Three specific questions were addressed in the current study. First, what is the relationship between strain and torque? Second, does the relationship between strain and torque change during the period of hindlimb unloading with exercise? Third, are the strain magnitudes in the range generally regarded to be osteogenic? This project is part of a larger effort aimed at assessing the efficacy of the muscle stimulation method as a countermeasure for the negative musculoskeletal effects of mechanical unloading.