Effects of leg strength and bicycle ergometry exercise on cardiovascular deconditioning after 30-day head-down bed rest

The purpose of this study is to determine if the intermittent leg muscular strength exercise and bicycle ergometry exercise could attenuate cardiovascular deconditioning induced by prolonged −6° head-down bed rest (HDBR). Fifteen male subjects were randomly allocated into group A (n=5, 30 days HDBR without exercise), group B (n=5, 30 days HDBR with leg muscular strength exercise) and group C (n=5, 30 days HDBR with bicycle ergometry exercise). The orthostatic tolerance (OT) was determined by +75°/20 min head-up tilt (HUT) test and the submaximal exercise capacity was determined by bicycle ergometry before and after HDBR. The results were as follows: (1) Compared with that before HDBR, OT time decreased dramatically by 57.6% (p<0.001) after HDBR in group A, while it decreased by 36.4% (p=0.084) in group B and by 34.7% (p=0.062) in group C. (2) Compared with that before HDBR, the submaximal exercise time decreased significantly by 17.7% (p<0.05) and 21.1% (p<0.05) in groups A and B, respectively, after HDBR. However, it had no change (+1.3%, p>0.77) in group C. (3) compared with that before HDBR, the changes of heart rate (HR) and blood pressure were slightly improved in group B and C, while deteriorated in group A during orthostatic test and exercise test after HDBR. The results indicate that leg muscular strength exercise and bicycle ergometry exercise could partially attenuate the cardiovascular deconditioning induced by 30 d HDBR, and the latter exercise training could fully provide the protection for the loss of exercise capacity.