Skeletal muscle is not only important for our ability to move, it also plays a major role in metabolism. Under normal conditions, the routine processes of muscle growth (hypertrophy) and breakdown (atrophy) are in balance. While many of us are aware that exercise and healthy diets promote muscle growth, diseases and sedentary lifestyles can promote muscle atrophy. Studies examining the effects of heat on muscle – from environmental heat, direct application of heat packs, immersion in water, etc – have found that heat can improve hypertrophy and prevent atrophy. The effects of heat appear to be are especially pronounced if used in combination with resistance training exercises.
Recently, a review published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology examined whether it is heat or exercise (or both) that improve muscle hypertrophy while preventing atrophy.
Heat shock proteins, HSPs for short, are a group of proteins that play an important role in an animal’s ability to deal with stress. They help shield proteins in the body from folding incorrectly and help improve the survival of cells. But heat is not the only stimulus that can activate HSPs, evidence also suggests that exercise may activate them too. Because of their protective role in cells, HSPs are speculated to prevent muscle loss with aging. Damage to HSPs or the genes that encode them, on the other hand, may contribute muscle diseases. Intriguingly, studies have shown that because certain forms of HSPs prevent cell death, their inhibition can disrupt breast cancer cells. At the same time, their ability to prevent cell death is what helps reduce muscle atrophy.
It should be noted that studies targeting HSPs have been mainly focused on cell culture models and animal studies, so there is still much to be learned about the potential of these proteins in humans. It should also be noted that a consensus has not yet been reached on whether exposure to heat increases muscle mass in humans as not all studies agree.
If this link holds up, I wonder if humans will become more muscular with climate change??
ZJ Fennel, FT Amorim, MR Deyhle, PS Hafen, CM Mermier. The heat shock connection: Skeletal muscle hypertrophy and atrophy. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology – Special topic: Don’t Deny Your Inner Environmental Physiologist: Investigatng Physiology with Environmental Stimuli. 323(1): R133-R148, 2022. https://doi.org/10.1152/ajpregu.00048.2022