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Muscle loss can occur as part of a disease process, trauma, or aging. Although exercise can prevent muscle loss, some medical conditions or physical limitations can make exercise difficult or even impossible. Findings from a new study indicate that hyperthermia may preserve or increase muscle mass and increase mitochondrial biogenesis.

Hyperthermia is a state of elevated core body temperature that activates molecular mechanisms that mitigate protein damage and drive the body’s in-house repair systems. Mitochondrial biogenesis is the process by which new mitochondria are made inside cells. Many factors can activate mitochondrial biogenesis including exercise, hyperthermia, and others.

The study involved nine healthy young men (average age, 35 years) who underwent two 60-minute sessions of passive heat treatment, separated by one week. One session was a whole-body treatment at 44˚C to 50˚C (111˚F to 122˚F) and 50 percent humidity. The other session was a single-leg treatment using a water-perfused suit at approximately 50˚C (122˚F). The authors of the study monitored core, skin and quadriceps muscle temperatures throughout the sessions and took muscle biopsies before, 30 minutes after, and three hours after the heat treatments.

The whole-body heat treatment switched on the activity of molecules involved in the Akt/mTOR biological pathway, a critical regulator in maintaining skeletal muscle mass. It also increased the expression of heat shock proteins and Nrf2. Nrf2 is a cellular protein that regulates the expression of antioxidant and stress response proteins. Its activity is an indicator of mitochondrial biogenesis. These changes were not evident when the participants received single-leg heat treatment, suggesting that whole-body hyperthermia elicits systemic improvements involved in muscle maintenance and mitochondrial health.

Interestingly, whole-body heat inhibited the activity of some FOXO proteins and switched on the activity of some genes involved in atrophy. Further study is needed to determine the full effects of whole-body hyperthermia on muscle atrophy.

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