fiber diameter and overall muscle volume), show the exercise countermeasures did not provide
the intensity needed to maintain calf muscle performance and structure (Trappe 2009 and Fitts
2010). Fast-twitch muscle fibers contract quickly but get tired quickly so a substantial
microgravity-induced muscle fiber shift
from the slow to fast type over long-
duration spaceflight would be
physiologically harmful and would increase
the crew’s risk of injury, impacting mission
objectives. After several ISS missions and
long-term bed rest experiments in the last
decade, enough data now exists to warrant
changes to the astronaut exercise regimen.
Since completing this study, a second
treadmill was added, the Combined
Operational Load-Bearing External
Resistance Treadmill (COLBERT) to ISS and
an improved resistance exercise device,
the Advanced Resistive Exercise Device
(ARED). This allows for greater
musculoskeletal loading during exercise. A new high-intensity, low-volume resistance and
aerobic exercise program is also being implemented. The latest regimen alternates days of high-
intensity interval training with continuous aerobic exercise (opposed to mostly continuous
aerobic exercise) and 3 days/week of high-intensity resistance training (opposed to 3-6
days/week at lower intensity). Ongoing research is investigating the effectiveness of the new
exercise program for protecting skeletal muscle health over long stays aboard the ISS (Bagley
2012).
PUBLICATION(S)
Fitts RH, Colloton PA, Trappe SW, Costill DL, Bain JL, Riley DA. Effects of prolonged spaceflight
on human skeletal muscle enzyme and substrate profiles. Journal of Applied Physiology.
September 1, 2013; 115(5):667-679. doi: 10.1152/japplphysiol.00489.2013.
Bagley JR, Murach KA, Trappe SW. Microgravity-induced fiber type shift in human skeletal
muscle. Gravitational and Space Biology. 2012;26:34-40.
Fitts RH, Trappe SW, Costill DL, et al. Prolonged spaceflight-induced alterations in the structure
and function of human skeletal muscle fibers. Journal of Physiology. 2010;588:3567-3592. doi:
10.1113/jphysiol.2010.188508.
Trappe SW, Costill DL, Gallagher PM, et al. Exercise in space: Human skeletal muscle after 6
months aboard the International Space Station. Journal of Applied Physiology. January 15, 2009;
106: 1159-1168. doi: 10.1152/japplphysiol.91578.2008.
This investigation is complete and all results are published.
ISS030E148397 – European Space Agency astronaut
Andre Kuipers, Expedition 30 flight engineer, prepares to
exercise in the Tranquility node of the International Space
Station (ISS), using the Advanced Resistive Exercise
Device (ARED).