The 4 hour work week blog have published a comprehensive and detailed breakdown of how heat can be used to increase growth hormone, muscular hypertrophy, endurance, and otherwise aid performance. The study is by Rhonda Perciavalle Patrick, Ph.D, she says that:
Increasing your core temperature for short bursts is not only healthful, it can also dramatically improve performance.
This is true whether it’s done in conjunction with your existing workout or as an entirely separate activity.
She explains that heat acclimatization has a positive effect on physical endurance, even causing physiological adaptations including:
Improved cardiovascular mechanisms and lower heart rate.1
Lower core body temperature during workload (surprise!)
Higher sweat rate and sweat sensitivity as a function of increased thermo-regulatory control.
Increased blood flow to skeletal muscle (known as muscle perfusion) and other tissues.2
Reduced rate of glycogen depletion due to improved muscle perfusion.
Increased red blood cell count (likely via erythropoietin).
Increased efficiency of oxygen transport to muscles.4
In the video above Rhonda Patrick explains how conditioning the body to heat stress through sauna use, called “hyperthermic conditioning” causes adaptations that increase athletic endurance (by increasing plasma volume and blood flow to heart and muscles) and muscle mass (by boosting levels of heat shock proteins and growth hormone). She also discusses the profound effects of hyperthermic conditioning on the brain including cognitive function.
The main positive thing that exposure to the heat of the sauna does is increase nutrient delivery to muscles thereby reducing the depletion of glycogen stores. It also reduces heart rate and core temperature during workload. Both of these enhance endurance in physical pursuits. This is a good reason for weight lifters and athletes to get down to Spa Experience for a Thermal Spa Experience.