This was a randomized controlled experiment; group assignment was nonblinded with the exception of testosterone, which was administered in a double-blind manner. The study was approved by both the NASA Johnson Space Center and University of Texas Medical Branch institutional review boards, and all subjects provided written informed consent.
The study protocol and screening process is described in detail in the companion paper (4 (link)). In brief, potential subjects were prescreened using an online application or via telephone interviews conducted by the NASA Johnson Space Center Test Subject Facility nursing staff. Candidates who met the basic inclusion criteria were asked to complete a second application, which included a log of their daily physical activity, consent for a background check, health history questionnaire, and a NASA-modified Air Force Class III physical examination. Qualified study candidates performed an upright peak cycle ergometry test and an isokinetic knee extension test at 60°·s−1. Minimum levels of cardiorespiratory fitness (peak aerobic capacity ( ) >30 mL·kg−1 min −1) and lower body muscle strength relative to body mass (knee extension >2.0 N·m·kg−1) were required to enter the study; these fitness levels represent the lower end of the range in the astronaut corps.
After initial testing, participants were randomized to 1 of 4 intervention groups. Three exercise groups were asked to perform the same high-intensity exercise prescription 6 d·wk −1 during 70 d of bed rest, beginning on the first day in bed. One group used traditional exercise equipment similar to that found on the ISS with no supplementation (EX), the second group used the traditional exercise equipment and was given a testosterone supplementation (ExT), and the third group used a single compact flywheel rowing and resistance exercise device (FLY). The fourth group consisted of control subjects (CONT) who participated in all pre–,in–, and post–bed rest testing but did not perform any exercise intervention. After 2–3 wk of dietary acclimation and familiarization with the exercise hardware, protocols, and study procedures, subjects were confined to 70 d of 6° head-down tilt bed rest. Here, we present pre– and post–bed rest muscle, bone, and cardiovascular outcomes.
The study protocol and screening process is described in detail in the companion paper (4 (link)). In brief, potential subjects were prescreened using an online application or via telephone interviews conducted by the NASA Johnson Space Center Test Subject Facility nursing staff. Candidates who met the basic inclusion criteria were asked to complete a second application, which included a log of their daily physical activity, consent for a background check, health history questionnaire, and a NASA-modified Air Force Class III physical examination. Qualified study candidates performed an upright peak cycle ergometry test and an isokinetic knee extension test at 60°·s−1. Minimum levels of cardiorespiratory fitness (peak aerobic capacity ( ) >30 mL·kg−1 min −1) and lower body muscle strength relative to body mass (knee extension >2.0 N·m·kg−1) were required to enter the study; these fitness levels represent the lower end of the range in the astronaut corps.
After initial testing, participants were randomized to 1 of 4 intervention groups. Three exercise groups were asked to perform the same high-intensity exercise prescription 6 d·wk −1 during 70 d of bed rest, beginning on the first day in bed. One group used traditional exercise equipment similar to that found on the ISS with no supplementation (EX), the second group used the traditional exercise equipment and was given a testosterone supplementation (ExT), and the third group used a single compact flywheel rowing and resistance exercise device (FLY). The fourth group consisted of control subjects (CONT) who participated in all pre–,in–, and post–bed rest testing but did not perform any exercise intervention. After 2–3 wk of dietary acclimation and familiarization with the exercise hardware, protocols, and study procedures, subjects were confined to 70 d of 6° head-down tilt bed rest. Here, we present pre– and post–bed rest muscle, bone, and cardiovascular outcomes.
