I'm not sure how much time we're going to have to discuss homeostasis but I thought I'd raise an interesting topic here - what is it that limits human athletic performance? Well it may surprise you but at the very top levels of performance for endurance athletes it appears that when the weather is warm and humid they are approaching physical limits for simply shedding heat.
In 1996 a paper was published that calculated the heat production by marathon runners and the rate at which that heat is lost by convection, radiation and evaporation. As the temperature, and particularly the humidity, increased so heavier athletes were calculated to be unable to maintain heat balance whilst maintaining a world class marathon pace (2hrs10mins or about 4.55 per mile). Dennis and Noakes (1999) expanded this study and pointed out that under the conditions of the 1996 summer Olympics in Atlanta (25 degrees C and 70% humidity) a 65kg (140 pounds) runner would have been right on the borderline for being able to maintain heat balance. A lighter runner would have had less of a problem because lighter runners have a dual advantage in the heat. Heat production depends on body mass and heat loss depends on surface area and so lighter runners both generate less heat and lose heat quicker.
The unexpected winner in Atlanta (seen above) was the 43 kg (95 pound) Josiah Thugwane of South Africa, who narrowly beat the 45kg (99 pound) South Korean Lee-Bong Ju.
The reason this came to mind was that I was reading an article about the pollution in Beijing and it was pointing out that the pollution may be a small problem compared to the heat and humidity. Summer temperatures in Beijing routinely pass 30 degrees Celsius (86 degrees Fahrenheit) and humidity can be 80 percent. If the 2008 Olympic marathon is run under these conditions, and I believe it is currently scheduled as a morning race - which is risky given that it will therefore get hotter over the course of the race - expect the winner to be one of the lighter athletes. A lot of people expect a good performance from Ryan Hall given his great race in London last week (2:06 - second fastest time by an American ever in only his third marathon) but at 130 pounds he might be struggling to run 2:15 if conditions are bad. If conditions are warm and humid expect a world class field to turn in a relatively slow time (2:12-2:14) and the winner to be not one of the top favorites but the lightest runner who is capable of competing at the top level.