Supplementary Material for: Impact of 14 days of bed rest in older adults and an exercise countermeasure on body composition, muscle strength and cardiovascular function: Canadian Space Agency standard measures

Introduction: Head-down bed rest (HDBR) has long been used as an analog to microgravity and it also enables studying the changes occurring with aging. Exercise is the most effective countermeasure for the deleterious effects of inactivity. The aim of this study was to investigate the efficacy of an exercise countermeasure in healthy older participants on attenuating musculoskeletal deconditioning, cardiovascular fitness level and muscle strength during l4 days of HDBR as part of the standard measures of the Canadian Space Agency.
Methods: Twenty-three participants (12 males and 11 females), aged 55-65 years, were admitted for a 26-day inpatient stay at the McGill University Health Centre. After 5 days of baseline assessment tests, they underwent 14 days of continuous HDBR followed by 7 days of recovery with repeated tests. Participants were randomized to passive physiotherapy or an exercise countermeasure during the HDBR period consisting in 3 sessions per day of either high-intensity interval training (HIIT) or low-intensity cycling or strength exercises for the lower and upper body. Peak aerobic power (V̇O2peak) was determined using indirect calorimetry. Body composition was assessed by dual-energy X-ray absorptiometry (DXA) and several muscle group strengths were evaluated using an adjustable chair dynamometer. A vertical jump was used to assess whole-body power output and a tilt test to measure cardiovascular and orthostatic challenge. Additionally, changes in various blood parameters were measured as well as the effects of exercise countermeasure on these measurements.
Results: There were no differences at baseline in main characteristics between the control and exercise groups. The exercise group maintained V̇O2peak levels similar to baseline whereas it decreased in the control group following 14 days of HDBR. Body weight significantly decreased in both groups. Total and leg lean masses decreased in both groups. However, total body fat mass decreased only in the exercise group. Isometric and isokinetic knee extension muscle strength was significantly reduced in both groups. Peak velocity, flight height and flight time were significantly reduced in both groups with HDBR.
Conclusion: In this first Canadian HDBR study in older adults, an exercise countermeasure helped maintain aerobic fitness and lean body mass without affecting the reduction of knee extension strength. However, it was ineffective in protecting against orthostatic intolerance. These results support HIIT as a promising approach to preserve astronaut health and functioning during space missions, and to prevent deconditioning as a result of hospitalization in older adults.

引言：头部低垂卧床休息（HDBR）长期以来一直被用作微重力的模拟，同时亦有助于研究随着年龄增长而发生的变化。运动是抵消久坐危害的最有效对策。本研究的目的是探究在HDBR期间，对健康老年参与者实施运动对策的有效性，以减轻其肌肉骨骼功能衰退、心血管适能水平和肌肉力量，为期4天，作为加拿大航天局标准措施的一部分。

方法：23名参与者（男性12名，女性11名），年龄介于55至65岁之间，被纳入麦吉尔大学健康中心进行的为期26天的住院研究。在为期5天的基线评估测试后，他们接受了14天的连续HDBR，随后进行为期7天的恢复，并重复进行测试。参与者被随机分配到被动物理治疗或运动对策组，在HDBR期间，每日进行三次高强度间歇训练（HIIT）、低强度骑自行车或上下肢力量训练。通过间接测热法确定峰值摄氧量（V̇O2peak）。通过双能X射线吸收法（DXA）评估身体成分，并使用可调座椅测力计评估多个肌肉群的肌力。通过垂直跳跃评估全身功率输出，通过倾斜试验测量心血管和直立位挑战。此外，还测量了各种血液参数的变化，以及运动对策对这些测量结果的影响。

结果：在基线时，对照组和运动组在主要特征方面没有差异。运动组保持了与基线相似的V̇O2peak水平，而对照组在14天的HDBR后有所下降。两组的体重均显著下降。两组的总体和腿部瘦体重均有所减少。然而，只有运动组的总体脂肪质量显著下降。两组的等长和等速膝伸展肌力均显著降低。在HDBR期间，两组的峰值速度、跳跃高度和跳跃时间均显著降低。

结论：在加拿大对老年人群进行的首次HDBR研究中，运动对策有助于维持有氧适能和瘦体重，而不影响膝伸展肌力的减少。然而，它对防止直立不耐受无效。这些结果表明，高强度间歇训练（HIIT）作为一种有潜力的方法，有助于在太空任务中维持宇航员的健康和功能，以及防止老年住院患者发生去适应化。