Exercise and Testosterone Countermeasures to Mitigate Metabolic Changes during Bed Rest

Meghan E. Downs, Jessica M. Scott, Lori L. Ploutz-Snyder, Robert Ploutz-Snyder, Elizabeth Goetchius, Roxanne E. Buxton, Christopher P. Danesi, Kathleen M. Randolph, Randall J. Urban, Melinda Sheffield-Moore, E. Lichar Dillon

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)97-104
Number of pages8
JournalLife Sciences in Space Research
Volume26
DOIs
StatePublished - Aug 2020

Keywords

  • Energy Balance
  • Glucose Tolerance
  • Insulin Sensitivity
  • Metabolic Rate
  • Spaceflight

ASJC Scopus subject areas

  • Radiation
  • Ecology
  • Astronomy and Astrophysics
  • Agricultural and Biological Sciences (miscellaneous)
  • Health, Toxicology and Mutagenesis

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    Downs, M. E., Scott, J. M., Ploutz-Snyder, L. L., Ploutz-Snyder, R., Goetchius, E., Buxton, R. E., Danesi, C. P., Randolph, K. M., Urban, R. J., Sheffield-Moore, M., & Dillon, E. L. (2020). Exercise and Testosterone Countermeasures to Mitigate Metabolic Changes during Bed Rest. Life Sciences in Space Research, 26, 97-104. https://doi.org/10.1016/j.lssr.2020.03.008