Stress — Sauna – Summaries

Summary:

Sauna helps to induce hypertrophy (increase in size of muscle cells).
Oxidative stress (through exercise) is a source of protein degradation.
Heat acclimation reduces protein degradation (and stimulates hypertrophy) through:
- Induction of heat shock proteins.
- Induction of growth hormones.
- Improved insulin sensitivity.
Positive impact on longevity, brain, endurance, red blood cells
Removes toxins.

Hypertrophy

Increase in the size of muscle cells.
Accompanying increase in strength.
Hypertrophy generally involves an increase in cell size rather than the number of cells.
At any given time your muscles are performing a balancing act between new protein synthesis and degradation of existing proteins.
Ratio of protein synthesis to protein degradation determines whether muscle cells grow or shrink.
- Protein degradation occurs both during muscle use and disuse.

Oxidative Stress

Exercise triggers process of oxidative phosphorylation.
- Mitochondria suck in oxygen to produce ATP.
By-product of this process is the generation of oxygen free radicals.
- Superoxide and hydrogen peroxide (oxidative stress).
Major source of protein degradation.

Hypertrophy and heat acclimation

Heat acclimation reduces the amount of protein degradation.
Results in increase of net protein synthesis and, thus muscle hypertrophy.
Three ways:
- Induction of heat shock proteins.
- Robust induction of growth hormone.
- Improved insulin sensitivity.

Heat shock proteins (HSP)

Induced by heat.
Example of hormesis (protective stress response).
Promotes the expression of a gene called heat shock factor 1.
HSPs:
- Prevent damage by scavenging free radicals (oxidative stress reduction).
- Support cellular antioxidant capacity through its effects on maintaining glutathione.
- Repair misfolded, damaged proteins thereby ensuring proteins have their proper structure and function.

Induction of growth hormone

Increase in growth hormone, which leads to increase in IGF-1.
Two mechanisms by which IGF-1 promotes the growth of skeletal muscle:
- Activation of the mTOR pathway, which is responsible for protein synthesis.
- Activation of the Akt pathway, which inhibits protein degradation.
Major anabolic effects of growth hormone in skeletal muscle likely is second pathway: the inhibition of protein degradation (Akt pathway)

Increased insulin sensitivity

Insulin regulates glucose homeostasis.
- Particularly by promoting the uptake of glucose into muscle and adipose tissue.
Insulin also plays a role in protein metabolism, albeit to a lesser degree than IGF-1.
Insulin regulates protein metabolism in skeletal muscle by the two following mechanisms:
- Increases protein synthesis by stimulating the uptake of amino acids (particularly BCAAs).
- It decreases protein degradation through inhibition of the proteasome.
  - Protein complex inside cells that is largely responsible for the degradation of most cellular proteins.
- Major anabolic effects of insulin on skeletal muscle likely is second pathway: inhibition of protein degradation (proteasome).

Impact on longevity

Sauna associated with longevity by reducing all-cause mortality.
Higher levels of HSPs protects cells from a variety of cellular and environmental stressors.
Heat stress has also been shown to activate the longevity gene FOXO3.
FOXO3 increases the expression of many different genes that enable cells to deal with a variety of environmental and cellular stresses.

Impact on brain

Impact on endurance

Increases plasma volume and blood flow to the heart.
- Reducing heart strain and lower heart rate for given workload.
Increases blood flow to the skeletal muscles.
- Keeping them fueled with glucose, esterified fatty acids, and oxygen.
- Reducing dependence on muscle glycogen stores (“hit the wall” later).
It improves thermoregulatory control.
- Activating the sympathetic nervous system and increasing the blood flow to the skin and, thus the sweat rate.
- Sweating occurs at a lower core temperature.

Impact on red blood cells

Sources and links:

Summaries