Mekjavic Igor B, Eiken Ola, Mekjavic Polona Jaki, McDonnell Adam C
Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia.
Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada.
Exp Physiol. 2021 Jan;106(1):37-51. doi: 10.1113/EP087834. Epub 2020 Oct 5.
What is the central question of this study? Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest? What is the main finding and its importance? During 10-day bed rest, exposure to a simulated (normobaric hypoxia) altitude of ∼4000 m does not exert additional significant structural or functional effect on the weight-bearing muscles in females compared to those noted under normoxic conditions. Whereas males and females exhibit decrements in muscle cross-sectional area and mass during normoxic and hypoxic bed rest, a concomitant strength decrement was only observed in males.
This study investigated the effects of hypoxia on the known processes of adaptation of body composition and muscle function to normoxic inactivity. Females (n = 12) and males (n = 11) took part in the following interventions: hypoxic ambulation (HAMB; ∼4000 m); hypoxic bed rest (HBR; ∼4000 m) and normoxic bed rest (NBR). Prior to and immediately following each intervention, body composition, thigh and lower leg cross-sectional area (CSA) and isometric muscular strength were recorded. Participants lost body mass (HAMB: male -1.5 ± 0.9 kg, female -1.9 ± 0.7 kg; HBR: male -2.0 ± 1.8 kg, female -2.4 ± 0.8 kg; NBR: male -1.4 ± 1.3 kg, female -1.4 ± 0.9 kg) and lean mass (HAMB: male -3.9 ± 3.0%, female -3.4 ± 2.0%; HBR: male -4.0 ± 4.4%, female -4.1 ± 2.0%; NBR: male -4.0 ± 3.4%, female -2.2 ± 2.7%) with no between-condition or sex differences. Knee extension decreased for males in NBR compared to HAMB (HAMB: male -0.2 ± 9.1%, female 1.3 ± 4.9%; HBR: male -7.8 ± 10.3%, female -3.3 ± 10.9%; NBR: male -14.5 ± 11%, female -3.4 ± 6.9%). Loss of force during maximal voluntary contraction (MVC) in the knee extensors was significantly different between males and females following NBR. There were no other significant changes noted following the experimental interventions. There were no differences recorded between sexes in maximal MVC for elbow or ankle joints. Female lower leg CSA decreased following bed rest (HAMB: -4.5 ± 2.0%; HBR: -9.9 ± 2.6%; NBR: -8.0 ± 1.6%). These findings indicate that a 10-day hypoxic bed rest does not exert any significant additional effect on muscle atrophy when compared to NBR, except for female thigh CSA. In contrast to males, who exhibited a significant loss of muscle strength, no such decrement in strength was observed in the female participants.
本研究的核心问题是什么？女性和男性在常氧及低氧卧床休息后，是否表现出相似的肌肉减少症反应？主要发现及其重要性是什么？在为期10天的卧床休息期间，与常氧条件下相比，暴露于模拟海拔约4000米的（常压性低氧）环境对女性承重肌肉未产生额外的显著结构或功能影响。虽然男性和女性在常氧及低氧卧床休息期间肌肉横截面积和质量均有所下降，但仅在男性中观察到伴随的力量下降。
本研究调查了低氧对已知的身体成分和肌肉功能适应常氧不活动过程的影响。女性（n = 12）和男性（n = 11）参与了以下干预措施：低氧行走（HAMB；约4000米）；低氧卧床休息（HBR；约4000米）和常氧卧床休息（NBR）。在每次干预之前和之后立即记录身体成分、大腿和小腿横截面积（CSA）以及等长肌肉力量。参与者体重减轻（HAMB：男性-1.5±0.9千克，女性-1.9±0.7千克；HBR：男性-2.0±1.8千克，女性-2.4±0.8千克；NBR：男性-1.4±1.3千克，女性-1.4±0.9千克），瘦体重也减轻（HAMB：男性-3.9±3.0%，女性-3.4±2.0%；HBR：男性-4.0±4.4%，女性-4.1±2.0%；NBR：男性-4.0±3.4%，女性-2.2±2.7%），不同条件或性别之间无差异。与HAMB相比，NBR中男性的膝关节伸展度降低（HAMB：男性-0.2±9.1%，女性1.3±4.9%；HBR：男性-7.8±10.3%，女性-3.3±10.9%；NBR：男性-14.5±11%，女性-3.4±6.9%）。NBR后，男性和女性膝关节伸肌最大自主收缩（MVC）时的力量损失存在显著差异。实验干预后未观察到其他显著变化。肘关节或踝关节的最大MVC在性别之间无差异记录。卧床休息后女性小腿CSA降低（HAMB：-4.5±2.0%；HBR：-9.9±2.6%；NBR：-8.0±1.6%）。这些发现表明，与NBR相比，为期10天的低氧卧床休息除了对女性大腿CSA有影响外，对肌肉萎缩未产生任何显著的额外影响。与表现出显著肌肉力量损失的男性不同，女性参与者未观察到力量下降。
