Tips for running in warm weather at the Standard Chartered Mumbai Marathon: Part 1

The intent of this article is to address the problems runners face (especially full marathon runners) when running in heat and humidity, as is seen mid-race at the Standard Chartered Mumbai Marathon. The guidelines given below are timely, in that they will allow runners training for SCMM to prepare themselves for any pitfalls.

So what are the pitfalls of running in the heat?

Exercise in the heat

During exercise in a hot environment, metabolic heat produced by the exercising muscles is transported by the circulating blood to the surface of the body where it is released to the environment, by evaporation of sweat.

The primary drives for both the increased skin blood flow and increased body sweating are the thermal inputs which are sensed by receptors in the deep body core. These thermal signals are integrated in the brain (more specifically, the hypothalamus) and proper heat loss responses are effected. When exercise is prolonged, however, and body re-hydration is not adequate, the total blood volume may be compromised. In addition, as the core temperature increases during exercise, larger proportions of the blood volume are distributed to the skin surface, effectively reducing cardiac return and central blood volume.

Physiological Response

Oxygen is redirected via blood flow to your skin instead of your leg muscles. Thus, you have less energy to use for running, and your heart and lungs must work harder to compensate for the loss in oxygen. This results in a higher heart rate at a given pace and the inability to maintain the same pace as you did on a cooler day. While this same pace felt ‘easy’ in winter, it will seem ‘moderately hard’ in the heat.

When exposed to external heat, your body maintains equilibrium via perspiration. Sweat has a cooling effect on the body because it removes excess heat through evaporation.

When humidity is low, evaporation increases; when humidity is high, the rate of evaporation decreases and less cooling occurs. When you run, only 25% of the energy produced for powering your run is used for propelling you forward. The balance 75% is wasted away as heat.

Relative Performance of Runners

You must know that if the runner is heavier, then the amount of oxygen consumed (given per kg) at a given running speed will be more than, and in direct proportion, to that for a lighter runner. Hence, a 100 kg runner will produce twice as much heat as a 50 kg runner. It is one of the reasons why elite runners are necessarily small.

Fluid Balance

The overall goal largely remains to match fluid intake with fluid loss during a run. However, maintaining post-run body mass that’s less than 2% of your pre-run mass conveys appropriate hydration. Any more loss and you set yourself up for dehydration.

This is done most effectively by tracking your pre-run nude body weight compared to post-run nude weight (both weighing done after voiding your bladder). Carefully measure the fluid intake during your run and you can check to see if you hydrated enough.

Weight before (A); weight after (B)

Sweat rate in litres per hour = (A – B) ÷ running time in hours

Dehydration% = (A – B) x 100 / A.

If your weight loss is greater than 2 percent, it indicates you need to take in more fluid; your performance, especially at faster paces, starts to suffer significantly once you get past that amount of dehydration. It may also lead to painful cramps.

For part 2, click here.

Published with permission from Dumbelled.com.