Greenleaf J E, Ertl A C, Bernauer E M
Gravitational Research Branch (239-11), NASA, Ames Research Center, Moffett Field, CA 94035-1000, USA.
Aviat Space Environ Med. 1996 Apr;67(4):314-9.
Maintaining intermediary metabolism is necessary for the health and well-being of astronauts on long-duration spaceflights. While peak oxygen uptake (VO2) is consistently decreased during prolonged bed rest, submaximal VO2 is either unchanged or decreased.
Submaximal exercise metabolism (61 +/- 3% peak VO2) was measured during ambulation (AMB day-2) and on bed rest days 4, 11, and 25 in 19 healthy men (32-42 yr) allocated into no exercise (NOE, N = 5) control, and isotonic exercise (ITE, N = 7) and isokinetic exercise (IKE, N = 7) training groups. Exercise training was conducted supine for two 30-min periods per day for 6 d per week: ITE training was intermittent at 60-90% peak VO2; IKE training was 10 sets of 5 repetitions of peak knee flexion-extension force at a velocity of 100 degrees s-1. Cardiac output was measured with the indirect Fick CO2 method, and plasma volume with Evans blue dye dilution.
Supine submaximal exercise VO2 decreased significantly (p < 0.05) by 10.3% with ITE and by 7.3%* with IKE; similar to the submaximal cardiac output decrease of 14.5%* (ITE) and 20.3%* (IKE), but different from change in peak VO2 (+1.4% with ITE and -10.2%* with IKE) and decrease in plasma volume of -3.7% (ITE) and -18.0%* (IKE). Reduction of submaximal VO2 during bed rest correlated 0.79 (p < 0.01) with submaximal Qc, but was not related to change in peak VO2 or plasma volume.
Reduction in submaximal oxygen uptake during prolonged bed rest is related to decrease in exercise but not resting cardiac output; perturbations in active skeletal muscle metabolism may be involved.
维持中间代谢对于长期太空飞行中宇航员的健康和福祉至关重要。虽然在长期卧床休息期间峰值摄氧量（VO2）持续下降，但次最大摄氧量要么保持不变，要么下降。
在19名健康男性（32 - 42岁）中，于行走日（AMB第2天）以及卧床休息的第4、11和25天测量次最大运动代谢（峰值VO2的61±3%）。这些男性被分为无运动（NOE，N = 5）对照组、等张运动（ITE，N = 7）训练组和等速运动（IKE，N = 7）训练组。运动训练每天仰卧进行两个30分钟时段，每周进行6天：ITE训练以峰值VO2的60 - 90%进行间歇训练；IKE训练以100度/秒的速度进行10组，每组5次峰值膝关节屈伸力训练。心输出量采用间接Fick CO2法测量，血浆容量采用伊文思蓝染料稀释法测量。
仰卧次最大运动VO2在ITE组显著下降（p < 0.05）10.3%，在IKE组下降7.3%；类似于次最大心输出量在ITE组下降14.5%和在IKE组下降20.3%，但与峰值VO2的变化不同（ITE组增加1.4%，IKE组下降10.2%*）以及血浆容量在ITE组下降3.7%和在IKE组下降18.0%*不同。卧床休息期间次最大VO2的降低与次最大Qc的相关性为0.79（p < 0.01），但与峰值VO2或血浆容量的变化无关。
长期卧床休息期间次最大摄氧量的降低与运动减少有关，但与静息心输出量无关；活跃骨骼肌代谢的紊乱可能参与其中。
