This is an interesting theory, and makes sense. However, the heat dynamics of how we handle the heat can really change the level of playing field in its own way.
When we run in the heat, the accumulation too much heat. hampers performance. The margin between optimum cellular function and death from hyperthermia is very small.
The typical resting core temperature of humans & warm blooded mammals is 37c(98.6f)Metabolic enzymes function optimally at ~39c (102.2) (importance of warmup pre-exercise)
Performance starts to deteriorate at core temperatures beyond, you will die at 40.5c(105f)
Thus, we live and train close to our thermal death point!
In warm (hot), humid environments, knowing how to cope is essential to exercise performance.
An optimum ambient temperature range must exist at which racing results are quickest- warm enough that the working muscles function optimally, but cool enough that metabolic heat dissipates even at fast paces.
Thus optimum temperature for fast marathon performances appear to be at 54 -/+ 5f (12.3-/+2c) Times slow by ~1min (or more) per 7f above 54f.
Why is a low blood volume (from excessive sweating or insufficient hydration) bad for successful sport competition?
Decrease in cardiac output- (heart rate x stroke volume) thus, if stroke volume decreases due to low blood volume, heart rate must increase to ensure adequate blood flow
Blood normally perfuses BOTH working muscles (to provide 02 for energy metabolism) & skin for evaporative cooling)
The cardiovascular system must use the blood to provide O2 for energy metabolism and skin for evaporative cooling. 10% of blood flow goes to skin during exercise in the heat. Your skin blood flow increases in proportion to exercise intensity and heat production. (During a hot day sweat rate = .5 - 1.5 liters per hour. = 8 - 25ml per minute)
If you begin to sweat and loose fluids, blood volume gets lower and lower. You begin to have less blood flow to the muscles and to skin. You cannot have heat accumulate and the body’s thermoregulation has a choice. If blood volume is critically low, it cannot have heat loss and will shut down the organism or it will preferentially shift fluid to skin. Working muscles get less blood flow. Pace slows down. (i.e. The results decrease in muscles blood flow slows the maintainable pace and renders the athlete noncompetitive - P. Radcliffe at Athens!??)
Power output decreases (<20%) with dehydration either because of glycogen depletion or an inability to use it.
There are negative effects of any amount of dehydration. Need to drink enough to match sweat rate. (For every liter of dehydration (~2.2 pounds of weight loss), your heart rate will rise 8 beats per minute, core temperature increases 0.3C, and cardiac output decreases 1 L/min.
Whole body dehydration rather than dehydration of blood (decreased plasma vol.) causes the series of events that impair body heat dissipation.
Other than the fact that your blood volume is low,the ability to utilize fats efficently are effected and your reliance on carbohydrate(glycogenolysis) stores increases. As you get hot, catecholimines increase, thus increasing . Total carbohydrate use increases in the heat, due mainly to muscle glycogen utilization.
It seems in hot/humid enviornments, those who can regulate heat accumulation and clearance the best are the ones whom perform better.