Background/Objectives

: Exercise is a front-line countermeasure used to maintain astronaut health during long-duration spaceflight; however, reductions in metabolic health still occur. Accordingly, we evaluated serial changes in metabolic parameters in a spaceflight analog and evaluated the efficacy of exercise with or without the addition of low-dose testosterone treatment on mitigating adverse metabolic changes.

Subjects/Methods

: Healthy young (<55 years) men were randomly assigned to one of three groups during 70-days of strict, diet controlled, 6° head-down bed rest: Control (CON, n=9), exercise plus testosterone countermeasure (TEX, n=8), or exercise countermeasure plus placebo (PEX, n=9). Basal metabolic rate (BMR), glucose tolerance, and insulin sensitivity were measured before, during, and after bed rest. Exercise energy expenditure and excess post-exercise oxygen consumption were measured in TEX and PEX subjects during bed rest.

Results

: Leptin decreased during bed rest (Pre to BR+0 changed from 6.9 ± 5.1, 5.8 ± 4.2, and 4.7 ± 4.1 to 7.9 ±3.6, 6.5 ± 4.6, and 4.1 ±3.0 ug• L⁻¹ for CON, PEX, and TEX respectively). Bed rest induced a decrease in BMR (Pre to BR57 changed from 1655 ± 212, 1629 ± 108, and 1706 ± 146 to 1476 ± 166, 1668 ± 142, and 1603 ± 132 kcal • day⁻¹ ± 95%CI for CON, PEX, and TEX respectively). Similarly, bed rest negatively affected glucose metabolism assessed by 2hr OGTT glucose (Pre to BR66 changed from 6.29 ± 0.72, 5.13 ± 0.72, and 5.87 ± 0.73 to 6.62 ± 0.72, 5.83 ± 0.72, and 7.08 ± 0.72 mmol • L⁻¹ ± 95%CI). Reambulation following bed rest positively affected glucose tolerance in CON (2hr OGTT glucose at BR+12: 5.3 ± 0.72, 6.42 ± 0.73, and 6.04 ± 0.73 mmol • L⁻¹ ± 95%CI). Testosterone protected against bed rest induced insulin resistance (HOMA-IR from Pre to BR+66 changed from 1.74 ± 0.54, 1.18 ± 0.55, and 1.45 ± 0.56 to 2.24 ± 0.56, 1.47 ± 0.54, and 1.07 ± 0.54).

Conclusion

: This study confirmed that inactivity during 70 days of head-down bed rest adversely affects metabolic health. The daily exercise countermeasures were beneficial but not completely protective of bed rest induced decrements in metabolic health. Supplementary countermeasures such as testosterone may provide additional benefits not provided by exercise alone.

中文翻译：

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运动和睾酮对策以减轻卧床休息期间的代谢变化。

背景/目标

：运动是宇航员在长时间航天飞行中保持健康的一线对策；然而，代谢健康的下降仍然发生。因此，我们评估了航天模拟中代谢参数的连续变化，并评估了添加或不添加低剂量睾酮治疗对减轻不良代谢变化的锻炼效果。

主题/方法

：健康的年轻（<55 岁）男性在 70 天的严格、饮食控制、6° 低头卧床休息期间被随机分配到三组之一：对照组（CON，n=9），运动加睾酮对策（TEX , n=8) 或运动对策加安慰剂 (PEX, n=9)。在卧床休息之前、期间和之后测量基础代谢率（BMR）、葡萄糖耐量和胰岛素敏感性。在卧床休息期间测量 TEX 和 PEX 受试者的运动能量消耗和运动后过量耗氧量。

结果

：瘦素卧床期间降低（前为BR + 0从6.9±5.1改变，5.8±4.2和4.7±4.1到7.9±3.6，6.5±4.6和4.1±3.0微克•L ^-1为CON，PEX，和TEX）。卧床休息导致 BMR 降低（前到 BR57 从 1655 ± 212、1629 ± 108 和 1706 ± 146 变为 1476 ± 166、1668 ± 142 和 1603 ± 132 kcal • 天^-1 ± 95%CI PEX 和 TEX）。通过2小时OGTT葡萄糖评估同样，卧床休息负面影响葡萄糖代谢（预至BR66从6.29±0.72变化，5.13±0.72，和5.87±0.73 6.62±0.72，5.83±0.72，和7.08±0.72毫摩尔•L ^-1 ± 95% CI）。卧床休息后的再行走对 CON 的葡萄糖耐量产生积极影响（BR+12 时的 2 小时 OGTT 葡萄糖：5.3 ± 0.72、6.42 ± 0.73 和 6.04 ± 0.73 mmol • L^-1 ± 95% CI)。睾酮可防止卧床引起的胰岛素抵抗（从 Pre 到 BR+66 的 HOMA-IR 从 1.74 ± 0.54、1.18 ± 0.55 和 1.45 ± 0.56 变为 2.24 ± 0.56、1.47 ± 0.54 和 1.07 ± 0.54）。

结论

：这项研究证实，在 70 天低头卧床休息期间不活动会对代谢健康产生不利影响。日常锻炼对策是有益的，但不能完全保护卧床休息引起的代谢健康下降。补充对策如睾酮可能会提供单独运动无法提供的额外好处。