Twins Bed Rest Project: Gender differences in loss of leg strength and endurance during bed rest

Abstract

This study compared decreases in knee strength (KS) and endurance (KE) in male and female monozygous twins after 28d of bed rest (BR) with/without exercise within lower body negative pressure (LBNPEX) countermeasure. METHODS Fifteen pairs of twins, 8 male (27±5 yrs; 68.0±10.0 kg) and 7 female (24±3 yrs; 56.6±9.8 kg) were subjects. One sibling was randomly assigned to an exercise (EX) or non-exercise (CON) group. LBNPEX consisted of 40-min interval exercise @ 40–80% of pre-BR aerobic capacity 6d·wk−1. LBNP was adjusted to produce a footward force of 1.0–1.2 body weight. KS (5 reps @ 60°·s−1; peak torque) and KE (20 reps @ 120°·s−1; total work) tests were performed for extension (ext) and flexion (flx) pre and post BR. Absolute and % changes were calculated. RESULTS KS and KE did not significantly decrease in male and female EX groups. For the CON group, men had greater absolute decreases in KS and KE for ext (table). Only % change in KE ext was greater for men (−13±8) than women (−3±9). CONCLUSIONS These results support previous findings that men have greater absolute decreases in strength and endurance than women during BR. However, % changes were similar, except KE ext. The LBNPEX countermeasure was equally effective in men and women in preventing loss of KS and KE. Supported by NASA grant NAG9-1425 to ARH and by NIH grant MO1 RR00827 to the UCSD GCRC.