MUSCLE STRENGTH DURING BEDREST WITH AND WITHOUT MUSCLE EXERCISE AS A COUNTERMEASURE

Bedrest is known to be a useful experimental model for simulating weig htlessness and studying its effects on human skeletal muscle activity. We therefore conducted a study in which 12 healthy male subjects unde rwent 28 days of continuous exposure to 6 degrees head-down bedrest, O ur main objective was to test a set of preventive countermeasures for maintaining the stability of the human body. Of the subjects 6 perform ed deadlifts in the supine position for 30 to 45 min each day. The iso metric actions were performed for 5-30 s at 90, 120 and 150 degrees kn ee angles and isokinetic training at speeds of 30 and 180 degrees . s( -1). In vivo quadriceps muscle strength was measured under controlled experimental conditions with a commercial dynamometer. The hypothesis that intense daily isometric and isokinetic leg exercise and lower bod y negative pressure (LBNP) might serve to maintain muscle strength und er conditions of weightlessness was tested. Of the subjects 6, who did not perform any exercise, served as the control population under cond itions of simulated weightlessness, The results showed that a signific ant reduction (P less than or equal to 0.0001) in the muscle force [-1 0.3 (SD 6.7%)] occurred in the control group whereas no significant ch anges were observed in the trained group [+3.9 (6.8%)]. From these stu dies we conclude that intense muscle training and LBNP constitute effi cient countermeasures to compensate for the biomechanical effects of w eightlessness on human lower limbs and to limit other factors such as cardiovascular deconditioning.