The long-term goal of this study was to determine the therapeutic efficacy of testosterone at preserving lean muscle mass, muscle strength, and bone mineral density in healthy humans during space flight. Investigators examined the interactive or additive effects of the combination of testosterone and exercise on lean body mass, muscle strength, and bone health.
To achieve these goals investigators tested the following hypotheses before, during, and after 70 days of bed rest:
- Cycled testosterone replacement (weekly testosterone injections for two weeks, followed by two weeks off) in conjunction with exercise will have an additive effect in preventing loss of muscle mass and muscle strength in men representative of the astronaut population compared to exercise with placebo testosterone.
- Cycled testosterone replacement (weekly testosterone injections for two weeks, followed by two weeks off) in conjunction with exercise will have an additive effect in preventing loss of bone mass and alterations in markers of bone metabolism in men representative of the astronaut population compared to exercise with placebo testosterone.
To address these hypotheses investigators studied the following specific aims before, during, and after 70 days of bed rest:
- To determine the effect of cycled testosterone replacement in conjunction with resistance exercise during bed rest on muscle mass, muscle strength, and fatigue in men aged 24-55 years.
- To determine the effect of cycled testosterone replacement in conjunction with resistance exercise during bed rest on markers of bone metabolism and bone mass in men aged 24-55 years.
++ -- View more
Male volunteers were randomly assigned to one of three bed rest groups 1) non-exercising + placebo (control group), 2) exercise + placebo (exercise A group) , and exercise + testosterone (exercise B group) using a standard of care approach with NASA space flight nutritional requirements and standard exercise protocols as the control condition. A total of 24 subjects completed the study. Eight subjects were in each bed rest group.
Results suggest that exercise groups A and B appear protected against the bed rest-induced loss of lean body mass (LBM, total and legs) and increases in fat mass. The exercise A group, but not B, significantly increased LBM during bed rest. Effects on bone for both exercise groups wasn’t significant.
Bone mineral density
Cholesterol, high-density lipoprotein (HDL)
Cholesterol, low-density lipoprotein (LDL)
++ -- View more
Exercise-induced perceived fatigue
Follicle-stimulating hormone (FSH)
High-sensitivity c-reactive protein (hsCRP)
Insulin-like growth factor-binding protein 3 (IGFBP-3)
Lean body mass
Lean muscle mass
Luteinizing hormone (LH)
Prostate-specific antigen (PSA) test
Protein abundances, vastus lateralis tissue
Protein phosporylation, vastus lateralis tissue
Sex hormone-binding globulin (SBG)
Very-low-density lipoprotein (VLDL)
Crew health and performance is critical to successful human exploration beyond low Earth orbit.
The Human Research Program (HRP) investigates and mitigates the highest risks to human health
and performance, providing essential countermeasures and technologies for human space exploration.
Risks include physiological and performance effects from hazards such as radiation, altered gravity,
and hostile environments, as well as unique challenges in medical support, human factors,
and behavioral health support. The HRP utilizes an Integrated Research Plan (IRP) to identify
the approach and research activities planned to address these risks, which are assigned to specific
Elements within the program. The Human Research Roadmap is the web-based tool for communicating the IRP content.
The Human Research Roadmap is located at: https://humanresearchroadmap.nasa.gov/
+ Click here
for information of how this experiment is contributing to the HRP's path for risk reduction.