Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest?

Abstract

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 ∼4000m 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; ∼4000m); hypoxic bed rest (HBR; ∼4000m) 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±0.9kg, female -1.9±0.7kg; HBR: male -2.0±1.8kg, female -2.4±0.8kg; NBR: male -1.4±1.3kg, female -1.4±0.9kg) 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%). Thesefindings 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.