Comparison of a space shuttle flight (STS-78) and bed rest on human musclefunction

The purpose of this investigation was to assess muscle fiber size, composit ion, and in vivo contractile characteristics of the calf muscle of four mal e crew members during a 17-day spaceflight (SF; Life and Microgravity Scien ces Spacelab Shuttle Transport System-78 mission) and eight men during a 17 -day bed rest (BR). The protocols and timelines of these two investigations were identical, therefore allowing for direct comparisons between SF and t he BR. The subjects' age, height, and weight were 43 +/- 2 yr, 183 +/- 4 cm , and 86 +/- 3 kg for SF and 43 +/- 2 yr, 182 +/- 3 cm, and 82 +/- 4 kg for BR, respectively. Calf muscle strength was examined before SF and BR; on d ays 2, 8, and 12 during SF and BR; and on days 2 and 8 of recovery. Muscle biopsies were obtained before and within 3 h after SF (gastrocnemius and so leus) and BR (soleus) before reloading. Maximal isometric calf strength and the force-velocity characteristics were unchanged with SF or BR. Additiona lly, neither SF nor BR had any effect on fiber composition or fiber size of the calf muscles studied. In summary, no changes in calf muscle strength a nd morphology were observed after the 17-day SF and BR. Because muscle stre ngth is lost during unloading, both during spaceflight and on the ground, t hese data suggest that the testing sequence employed during the SF and BR m ay have served as a resistance training countermeasure to attenuate whole m uscle strength loss.