Surface electromyogram power spectrum changes in human leg muscles following 4 weeks of simulated microgravity

Surface electromyogram (EMG) spectrum changes in human tibialis anterior (TA) and gastroenemius medialis (GM) muscles were studied to investigate the effect of 4-week bed rest (BR) on muscle fatigability. An exhausting isometric test at 50% of the maximal voluntary contraction was performed by 12 clinically healthy men before and after BR. During this test, mean power frequency (MPF) calculated from surface EMG decreased linearly for TA and GM. When changes in MPF were expressed in terms of rate of decrease a significant difference appeared between TA and GM. Furthermore, as a result of BR, the shift in MPF increased significantly for GM (6.1% vs 10.4%) whereas it was not significantly changed for TA (28.6% vs 20.95%). Alterations in maximal torque were also observed with a more pronounced decrease for plantar-flexor (20.5%) compared with dorsiflexor (15.1%) muscles. These results would seem to indicate that simulated microgravity preferentially affects muscles having an antigravity function.