Chronic cold induces some similar effects to endurance exercise on body morphometrics and skeletal muscle structure in rats.

Cold exposure may serve as an alternative to exercise for maintaining muscle mass and function but how these interventions impact muscle structure independently or synergistically is not well understood. We examined the effect of cold (4 °C) and/or endurance exercise training for 5 weeks on body composition and histological characteristics of oxidative and glycolytic muscles in rats. Body mass, skinfold thickness, and tissue masses were measured. The proportion of fiber types, fiber cross-sectional area, and the activity of succinate dehydrogenase (SDH) were quantified in soleus and gastrocnemius muscles. Increases in body mass, skinfold thickness, and white adipose tissue mass relative to body mass were equivalent between untrained-cold and trained-cold rats and lower than untrained-warm rats. The relative mass of soleus and cross-sectional area of type I fibers were smaller in cold and exercised rats compared to untrained-warm rats. Cold exposure alone resulted in an increase in the relative mass of soleus, proportion of type IIa fibers, and SDH activity compared to warm rats. In gastrocnemius, the cross-sectional areas of type IIa and IIb fibers were smaller in trained-cold compared to untrained-warm rats. SDH activity was higher in untrained-cold compared to untrained-warm and trained-cold rats, but equivalent to trained-warm rats. Overall, the results indicate that cold temperature and exercise alone improve body morphometrics and may increase aerobic capacity of muscle. Cold temperature and exercise had synergistic effects in soleus but there were some antagonistic effects in gastrocnemius. The data suggest that cold or exercise alone may be beneficial for minimizing muscle atrophy.