CHARACTERISTICS AND PRELIMINARY-OBSERVATIONS OF THE INFLUENCE OF ELECTROMYOSTIMULATION ON THE SIZE AND FUNCTION OF HUMAN SKELETAL-MUSCLE DURING 30 DAYS OF SIMULATED MICROGRAVITY

  • 1 July 1989
    • journal article
    • research article
    • Vol. 60  (7) , 671-678
Abstract
During 30 days (d) of bedrest, the practicality of using electromyostimulation (EMS) as a deterrent to atrophy and strength loss of lower limb musculature was examined. An EMS system was developed that provided variable but quantifiable levels of EMS, and measured torque. The dominant leg of three male subjects was stimulated twice daily in a 3-d on/1-d off cycle during bedrest. The non-dominant leg of each subject acted as a control. A stimulator, using a 0.3 ms monophasic 60 Hz pulse waveform, activated muscle tissue for 4 s. The output waveform from the stimulator was sequenced to the knee extensors (KE), knee flexors (KF), ankle extensors (AE), and ankle flexors (AF), and caused three isometric contractions of each muscle group per minute. Subject tolerance determined EMS intensity. Each group received four 5-min bouts of EMS each session with a 10-min rest between bouts. EMS and torque levels for each muscle action were recorded directly on a computer. Overall average EMS intensity was 197, 197, 195, and 188 mA for the KE, KF, AF, and AE, respectively. Overall average torque development for these muscle groups was 70, 16, 12, and 27 Nm, respectively. EMS intensity doubled during the study, and average torque increased 2.5 times. Average maximum torque throughout a session reached 54% of maximal voluntary for the KE and 29% for the KF. Reductions in leg volume, muscle compartment size, cross-sectional area of slow and fast-twitch fibers, strength, and aerobic enzyme activities, and increased leg compliance were attentuated in the legs which received EMS during bedrest. These results indicate that similar EMS levels induce different torques among different muscle groups and that repeated exposure to EMS increases tolerance and torque development. Longer orientation periods, therefore, may enhance its effectiveness. Our preliminary data suggest that the efficacy of EMS as an effective countermeasure for muscle atrophy and strength loss during long duration space travel warrants further investigation.