Our muscles are continually waging a war between the growth of new muscle cells (protein synthesis) and degradation of our existing proteins. The key factor is our net protein synthesis which takes into account both new protein synthesis and degradation. ATE reduces the amount of protein degradation taking place and therefore boosts net protein synthesis as follows:
A.ATE creates increased muscle mass:
1.Increased heat shock proteins* (HSPs): Heat acclimation increases net protein synthesis and muscle growth.(14,15) Increased production of heat shock proteins (HSPs) promotes muscle growth and reduces protein degradation.(14,15) Protein degradation occurs naturally during both muscle use and disuse. HSPs induced by heat help to both prevent and repair damaged proteins. HSPs are used by the cells to counteract potentially harmful stimuli.(14,15) HSPs can prevent damage by scavenging free radicals and supporting cellular antioxidant capacities via their help in maintaining glutathione levels.(14,15) HSPs also repair misfolded and damaged proteins so proper structure and function is maintained.(14,15)
*Note: See appendix for additional information
2.Increased muscle mitochondria*: Research has shown that both heat exposure and high intensity exercise cause heat shock and oxidative stress (generation of O2− and H2O2). In addition, both exercise and ATE training promote mitochondrial biogenesis (2–3-fold increases in muscle mitochondria). (23,24,25).
3.Increased levels of human growth hormone* (HGH): ATE increases muscle growth by large induction of HGH.(12,13,5) Studies have shown that exercise in high heat (40 degrees C.) resulted in increased HGH concentrations from the resting value both in the first and last heat tests.(5) The studies also showed that resting aldosterone (HGH) concentration was increased after heat acclimation.(5) Another study showed that exercise in a heated (40 degrees C.) climatic chamber almost doubled plasma HGH from levels achieved with the same exercise done under thermo-neutral (23 degrees C.) conditions.(92) Studies have shown that the major anabolic effects of HGH in skeletal muscle may result from the inhibition of muscle protein degradation, which results in net increases in protein synthesis.(18) Another study concluded that the administration of HGH to athletes for four weeks decreased muscle protein oxidation and degradation by 50%.(28)
- Increased production of muscle proteins: Exercise in heat contributes to improved protein synthesis.(11,14,15), and heat acclimation increases net protein synthesis and muscle growth.(14,15) Stimulation of the uptake of amino acids into muscle cells increases protein synthesis.(55) An animal study
*Note: See appendix for additional information.
utilizing intermittent hyperthermia induced significant HSP in skeletal muscle which augmented muscle growth by 30%.(14) The animal study also showed that increased HSP expression can persist for 48 hours after heat shock.(14,15)
- Reduced protein degradation and protection against degenerative muscle tissue conditions: Muscle growth can be promoted by triggering the release of heat shock proteins (HSPs) which reduce the amount of protein degradation that naturally occurs during both muscle use and disuse.(14,15) Human growth hormone (HGH) also decreases protein degradation. Reduced protein degradation increases the net protein synthesis in the muscles and therefore promotes muscle growth.(14,15) It has also been shown that exercise in heat increases concentrations of HSPs, which may illustrate a cellular adaptation of heat acclimation in humans.(23) HSPs also help repair damaged proteins and help maintain proper protein structure and function, and thereby help protect against degenerative muscle tissue conditions.(14,15)
- Reverses age-related muscle atrophy (sarcopenia): Sarcopenia [age-related loss of muscle] affects about 10 percent of those over 60, with higher rates as age advances. Causes of the loss of muscle mass or strength include hormonal changes, sedentary lifestyles, oxidative damage, infiltration of fat into muscles, inflammation and resistance to insulin.(49) Exercise in heat contributes to improved protein synthesis. (11,14,15) Exercise in heat increases concentrations of HSPs, which may illustrate a cellular adaptation of heat acclimation in humans. (23)
- Reduces levels of lactic acid in the blood: Increased levels of lactate in muscles causes fatigue during exercise. Reduced lactate production can increase the capacity for prolonged physical activity. It is believed that this is because of increased blood flow to the muscles.(29) Exercise performed in a hot environment has been shown to reduce blood lactate levels.(16)
- Reduced muscle glycogen use: The reduced usage of glycogen by the muscles results from increased blood flow to the muscles.(7,8) Studies show that exercising in hot environments reduces muscle glycogen use by 40 to 50% and show reduced rates of glycogen depletion due to improved muscle perfusion. (7,8). Additional studies show that heat acclimation leads to sparing of muscle glycogen associated with enhanced ability to perform highly intense exercise following prolonged exertion in the heat.(7)
- Increased lactate threshold: Increased levels of lactate in muscles causes fatigue during exercise. Reduced lactate production can increase the capacity for prolonged physical activity (it is believed this is because of increased blood flow to the muscles).(29) Exercise performed in a hot environment has been shown to reduce blood lactate levels.(16)
- Improved recovery from muscle injury: To return to a healthy condition after injury, muscle regrowth must occur. Muscle regrowth after immobilization occurs as a result of elevated heat shock protein levels. Brain-derived neurotrophic factor*(BDNF) is also secreted by muscle cells and plays an important role in muscle repair and growth.(30) Studies show that exercise increases serum
*Note: See appendix for additional information.
BDNF.(86) This increase can be enhanced with exercise in the heat. Since permeability of the blood–brain barrier increases with exercise in the heat, it is believed that this causes a higher cerebral output of BDNF.(47) Exercise in heat increases concentrations of HSPs, which may illustrate a cellular adaptation of heat acclimation in humans. (23)
- Reduced neuro-motor degradation: Brain-derived neurotrophic factor (BDNF) also protects neuro-motors—the most critical elements in muscle– from degradation.(60) Studies show that exercise increases serum BDNF. (86) This increase can be enhanced with exercise in the heat. Since permeability of the blood–brain barrier increases with exercise in the heat, it is believed that this causes a higher cerebral output of BDNF.(47)
- Improved insulin sensitivity: Insulin is an endocrine hormone responsible for promoting the uptake of glucose into muscle and adipose tissue. Insulin is also important for protein metabolism and increasing protein synthesis by stimulating the uptake of amino acids into the muscle.(94). In overweight individuals, insulin levels are elevated because the tissues do not respond properly to insulin (“insulin insensitivity”). This condition impedes the ability of glucose to enter muscle cells, causes high blood sugar levels and increases in the amount of glucose entering fat cells.(10,29) Studies have shown that ATE helps to reduce insulin resistance by improving insulin sensitivity and decreasing muscle protein catabolism. Animal studies have found that 30 minutes heat exposure three times per week for a period of 12 weeks can result in a 31 percent decrease in insulin levels.(10) Lower insulin levels help maintain higher sensitivity to insulin and promote the entry of glucose into muscle cells.(10,29) Exercise has been shown to significantly reduce the risk of developing insulin resistance by improving glucose tolerance and insulin action in individuals predisposed to develop type 2 diabetes.(50)