Mixed
Current ISS exercise countermeasures (aerobic and resistance) are insufficient to prevent significant calf muscle atrophy, loss of force-generating capacity, and slow-to-fast fiber type transitions during 6-month spaceflight.
For Earth-based training, this highlights that 'exercise' is not a monolith; the specific type, intensity, and loading profile matter. If you are not seeing muscle maintenance or growth despite regular activity, evaluate if your current routine provides sufficient mechanical tension (especially resistance) to counteract unloading or detraining effects. Standard aerobic exercise alone is insufficient for preserving muscle mass.
These data show a reduction in calf muscle mass and performance along with a slow-to-fast fiber type transition in the gastrocnemius and soleus muscles, which are all qualities associated with unloading in humans. Future long-duration space missions should modify the current ISS exercise prescription and/or hardware to better preserve human skeletal muscle mass and function...
Why this rating
Direct measurement on human subjects (n=9) with pre/post comparisons, though sample size is small and specific to astronauts.
Source
Exercise in space: human skeletal muscle after 6 months aboard the International Space Station
Scott Trappe et al. · Journal of Applied Physiology · 2009
DOI 10.1152/japplphysiol.91578.2008
More from this paper
- Soleus muscle is more susceptible to atrophy and fiber type shifting than the gastrocnemius during long-duration spaceflight, exhibiting a 15% volume loss and a 17% decrease in MHC I fibers.Good
- Long-duration spaceflight induces a slow-to-fast myosin heavy chain (MHC) transition in both gastrocnemius and soleus muscles, characterized by a decrease in MHC I fibers and an increase in hybrid MHC I/IIa fibers.Good
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