Research
Mixed
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.
Muscle fiber type is plastic. Prolonged inactivity or unloading shifts muscles toward faster, less fatigue-resistant phenotypes. Recovery requires specific retraining to restore slow-twitch characteristics.
GoodSupportsHIGH confidence
There was a 12–17% shift in myosin heavy chain (MHC) phenotype of the gastrocnemius and soleus with a decrease (P < 0.05) in MHC I fibers and a redistribution among the faster phenotypes.
Why this rating
Direct single-fiber analysis on human subjects.
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
cohort · n=9Cited 445×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- 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.Good
- 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
Related findings · Mixed
- Bariatric surgery (VSG and RYGB) is the most effective and sustainable treatment for obesity, producing marked and sustained weight loss that non-surgical interventions cannot match.Strong
- Severely protein-deficient diets (2–3% energy) induce lean body mass loss and metabolic imbalance, whereas adequate protein intake (0.66 g/kg/d minimum) is a prerequisite for maintaining muscle, bone, and physiological function.Strong
- For patients with Class III obesity (BMI >39.9 kg/m2), metabolic bariatric surgery (MBS) is significantly more effective than any currently approved medication, with BilioPancreatic Diversion (BPD) showing the highest estimated weight loss.Strong
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →