My client and I had a little chat about why exercising in this hot weather feels so hard. My thoughts were that blood needs to be pumped to the periphery in order to dissipate heat via the skin, much more than usual, therefore exercising muscles are receiving less of the red stuff, and therefore less oxygen.
A quick read of the subject in an Idea Health & Fitness article backs this up, saying that humid conditions are especially difficult, as the air is already saturated with water. When your body has a choice to cool itself or maintain exercise intensity it chooses the former.
The Journal of Physiology 2008 nicely explains what is happening –
“As dynamic exercise and heat production continue, thermoregulatory demands add to the problem of integrative control, such that the demands of elevated body temperature for increasing skin blood flow are in competition with the metabolic demands to increase blood flow to active muscle.”
The same source states that increased heat production, combined with the limits to heat loss, can produce raised internal temperature, which effects the central nervous system and limits the ability to continue exercise. Lack of oxygen to exercising muscles also increases the rate of perceived exertion.
Further, fatigue is not the result of lack of blood to the muscles or of falling blood pressure, but of high brain temperature – sounds nasty!
If fluids lost through sweating are not replaced, dehydration along with increased heat can cause problems of cardiovascular control, and raises the risk of heat illness. Apparently, after about half an hour your body is unable to absorb fluid taken on board at a rate quick enough to offset the rate at which you lose it, so it is vital to be fully hydrated before you exercise.
Hydrating over normal levels before exercise helps the body to regulate body temperature during exercise and increases plasma (blood) volume to maintain cardiac output.
If possible, exercise during the cooler early mornings or later evenings.
Enjoy the sun safely while it lasts.