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Long-duration spaceflight causes wholesale physiologic deconditioning including decrements in muscle mass, muscle strength and function, aerobic capacity, and bone mineral density. Even the performance of near-daily exercise countermeasures is largely inadequate to prevent this degradation. Current exercise hardware on the International Space Station (ISS) employed to combat these maladaptations consists of a cycle ergometer (CEVIS), the second-generation treadmill (T2), and advanced resistive exercise device (ARED); crewmembers on the ISS have used these systems and previous legacy devices to exercise 6 d per week with 2.5 h per day allotted to exercise countermeasures. This represents a significant time commitment and reduces crewmembers’ availability to perform other important mission tasks. Higher intensity/lower volume aerobic intervals have been incorporated into ISS exercise prescriptions; however, velocity restrictions on the first ISS treadmill curtailed their usage and individual crewmember preferences limited ubiquitous implementation. Similarly, resistance exercise on the ISS was performed at lower intensities due to the loading limitations of the original resistive exercise device until the 2009 deployment of ARED which provides up to 272 kg of resistance; subsequently, up to 6-repetition maximum loads have been used.
The effectiveness of high intensity/low volume training (HIT) has been extensively documented in populations ranging from elite athletes to clinical patients. In addition to the time savings of shorter exercise sessions, there is evidence to suggest that HIT may elicit superior physiologic adaptations compared to traditional lower intensity/higher volume training. For instance, over a 6-week period (5 d/wk), Tabata et al. compared 60 min bouts of continuous exercise (70% VO2peak) to 7-8 intervals (20 s at 170% VO2peak /10 s rest). Despite cumulative exercise time of only ~2 h compared to 30 h for the continuous group, the HIT group increased both aerobic and anaerobic capacity whereas the continuous, high volume group only improved aerobic capacity. Somewhat longer duration intervals of 2-4 min have been shown to maintain or improve aerobic capacity during bed rest unloading and athletic training.
In light of the potential for similar if not superior physiologic protection despite diminished exercise volume, the purpose of this investigation was to compare physiologic outcomes after long-duration (~six months) spaceflight on the ISS in crewmembers who performed exercise countermeasures consisting of either 1) lower intensity/higher volume exercise (6 d/wk resistance exercise and 6 d/wk aerobic exercise) or 2) high intensity/lower volume exercise (3 d/wk resistance exercise and 6 d/wk aerobic exercise).
Tabata I, Nishimura K, Kouzaki M et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc. 1996;28(10):1327-30.
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De Witt JK, English KL, Crowell JB, Kalogera KL, Guilliams ME, Nieschwitz BE, Hanson AM, Ploutz-Snyder LL. "Isometric midthigh pull reliability and relationship to deadlift one repetition maximum." Journal of Strength and Conditioning Research. 2018 Feb;32(2):528-33. https://journals.lww.com/nsca-jscr/Abstract/2018/02000/Isometric_Midthigh_Pull_Reliability_and.28.aspx ; PubMed PMID: 27548797 , Feb-2018
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Dillon EL, Sheffield-Moore M, Durham WJ, Ploutz-Snyder LL, Ryder JW, Danesi CP, Randolph KM, Gilkison CR, Urban RJ. "Efficacy of testosterone plus NASA exercise countermeasures during head-down bed rest." Medicine and Science in Sports and Exercise. 2018 Sep;50(9):1929-39. https://doi.org/10.1249/MSS.0000000000001616 ; PubMed PMID: 29924745; PubMed Central PMCID: PMC6095739 , Sep-2018
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Cromwell RL, Scott JM, Downs M, Yarbough PO, Zanello SB, Ploutz-Snyder L. "Overview of the NASA 70-day Bed Rest Study." Med Sci Sports Exerc. 2018 Sep;50(9):1909-19. Epub 2018 Mar 22. https://doi.org/10.1249/MSS.0000000000001617 ; PubMed PMID: 29570535 , Sep-2018
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Ploutz-Snyder LL, Downs M, Goetchius E, Crowell B, English KL, Ploutz-Snyder R, Ryder J, Dillon EL, Sheffield-Moore M, Scott JM. "Exercise training mitigates multi-system deconditioning during bed rest." Med Sci Sports Exerc. 2018 Sep;50(9):1920-8. Epub 2018 Mar 26. https://doi.org/10.1249/MSS.0000000000001618 ; PubMed PMID: 29924746
, Sep-2018
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Articles in Peer-reviewed Journals
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Scott JM, Martin D, Ploutz-Snyder R, Downs M, Dillon EL, Sheffield-Moore M, Urban RJ, Ploutz-Snyder LL. "Efficacy of exercise and testosterone to mitigate atrophic cardiovascular remodeling." Medicine and Science in Sports and Exercise. 2018 Sep;50(9):1940-9. Epub 2018 Mar 22. https://doi.org/10.1249/MSS.0000000000001619 ; PubMed PMID: 29570536; PubMed Central PMCID: PMC6095799 , Sep-2018
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Articles in Peer-reviewed Journals
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Dillon EL, Sheffield-Moore M, Durham WJ, Ploutz-Snyder LL, Ryder JW, Danesi CP, Randolph KM, Gilkison CR, Urban RJ. "Efficacy of testosterone plus NASA exercise countermeasures during head-down bed rest." Med Sci Sports Exerc. 2018 Sep;50(9):1929-39. Epub 2018 Mar 26. https://doi.org/10.1249/MSS.0000000000001616 ; PubMed PMID: 29924745; PubMed Central PMCID: PMC6095739 , Sep-2018
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Mulavara AP, Peters BT, Miller CA, Kofman IS, Reschke MF, Taylor LC, Lawrence EL, Wood SJ, Laurie SS, Lee SMC, Buxton RE, May-Phillips TR, Stenger MB, Ploutz-Snyder LL, Ryder JW, Feiveson AH, Bloomberg JJ. "Physiological and functional alterations after spaceflight and bed rest." Med Sci Sports Exerc. 2018 Sep;50(9):1961-80. Epub 2018 Apr 3. https://doi.org/10.1249/MSS.0000000000001615 ; PubMed PMID: 29620686
, Sep-2018
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English KL, Lee SMC, Loehr JA, Ploutz-Snyder RJ, Ploutz-Snyder LL. "Isokinetic strength changes following long-duration spaceflight on the ISS." Aerosp Med Hum Perform. 2015 Dec;86(12 Suppl):A68-A77. https://doi.org/10.3357/AMHP.EC09.2015 ; PMID: 26630197 , Dec-2015
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Ploutz-Snyder L. "Evaluating countermeasures in spaceflight analogs." J Appl Physiol (1985). 2016 Apr 15;120(8):915-21. https://doi.org/10.1152/japplphysiol.00860.2015 ; PMID: 26662054 , Apr-2016
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Scott JM, Martin DS, Ploutz-Snyder R, Matz T, Caine T, Downs M, Hackney K, Buxton R, Ryder JW, Ploutz-Snyder L. "Panoramic ultrasound: A novel and valid tool for monitoring change in muscle mass." J Cachexia Sarcopenia Muscle. 2017 Jun;8(3):475-81. https://doi.org/10.1002/jcsm.12172 ; PMID: 28052593; PMCID: PMC5476852 , Jun-2017
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