The Astronaut Center of China 90-d Head-Down Bed Rest: Overview, Countermeasures, and Effects

Countermeasures in weightlessness are a predominant technique for long-term residency in space. Head-down bed rest (HDBR) has long been used to simulate the physiological effects of spaceflight and test the efficacy of countermeasures. In 2019, the Astronaut Center of China (ACC) has held a 90-d HDBR on the effects of exercises' intervention. Thirty-six subjects were recruited and randomized into 5 intervention groups: (a) control, (b) aerobic exercises, (c) resistance exercises, (d) concurrent aerobic and lower load resistance exercises, and (e) concurrent aerobic and high-load resistance exercises. Moreover, exercise interventions were performed in supine or 6 degrees head-down tilt. They were provided with plain medical, psychological, and nutritional supports during the experiment. In addition, cardiovascular and pulmonary functions, muscle strength, bone density, and neuro-immune-endocrine functions were assessed over time. Subjects were monitored by clinical evaluations, psychological assessments, and nutritional status evaluations. All subjects spent 138 d in the bed rest study laboratory and received 2 follow-up tests per 3 months in the home recovery period. It was found that exercises in the 4 groups were effective interventions for aerobic capacity compared with control. The resistance exercises or concurrent aerobic and high-load resistance exercises improved isometric maximal voluntary contraction. However, the protection against bone loss still needs further exploration. Appropriate psychosocial and nutrition support techniques are worth to be reinforced.