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Heat, stretching and warmups
by on Monday, June 30, 2014  (2 comments)

In an ironic twist, a day after my post on summer running went live I came across a study on what about the heat affects us. Also this week, pre-exercise static stretching and a better way to warm up?

First, what is it about the heat that affects our running? For the longest time, we've been told it's that our core temperature rises to near dangerous levels and our bodies shut down to protect themselves.

Well, what if that's not the case?

There were no group differences in core temperature and heart rate response during the exercise trials.


This capacity difference appears to result from a magnified core to skin gradient via an environmental temperature advantageous to convective heat loss, and in part from an increased sweat rate.

In short, the study had runners running in temperatures of roughly 64, 79, 93 and 108 degrees farenheit. It found no statistically significant difference in core body temperature or heart rate between runners running at these different temperatures. What it did find was that the difference between core temperature and skin temperature was lower and sweat rate was higher in the higher temperatures. The suggested conclusion is that these factors, not core body temperature, are what actually affect our performance in the heat.

Of course, this is just one study. It would be nice to see some follow up to see if others can produce the same results.

Assuming these results can be reproduced, though, how might we act on this? Well, I've always been a fan of pouring cups of water over your head and/or body at aid stations when racing in the heat. That would help cool your skin, which according to this would help your performance. Anything else you can do to help cool your skin would, presumably, do the same. This is probably the mechanism by which those chill vests some elite athletes use before warm weather races work.

Second, does static stretching affect our performance

The going concern over pre-exercise static stretching is that our power output is reduced. Well, it is...in some cases.

Basically, this goes back to something I have been seeing a lot of recently. If you static stretch a muscle for more than 45 seconds, its power output is reduced. If you static stretch for less, no reduction in power output.

So, if you feel like you need static stretching pre-run, do it. Just don't hold it for too long. Personally, I've always felt better in races when I did some stretching pre-race but I don't hold the stretches for long. So my takeaway from this is keep doing what I've been doing. That's probably the takeaway most runners should get from this.

Finally, make sure you do some harder running in your warmups

I've long been a fan of warmups that increase in intensity. Start very easy, build up over time and finish with some strides at or slightly faster than race pace shortly before the start of the race. It's just the way I've been taught to do my warmups and it makes intuitive sense. You're preparing yourself to run hard so why wouldn't you run hard as part of that preparation?

Scott Douglas writes about a study to delve into this a little deeper with some interesting results.

In short, runners did some strides and moderately paced running as part of warmups twice. In once case, they wore weighted vests during the strides. In the other case, they did not. After wearing the weighted vests, their running economy and peak speed improved.

What to make of this? Should we all go out and buy weighted vests? One interesting idea that comes to mind for me is using skipping exercises for exaggerated power output. Another is doing something like Jay Johnson's lunge matrix, which I know he has mentioned as a good pre-race routine.

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Wow that abstract about core to skin temperature gradient is fun to read :-p I would guess your body uses more energy regulating core temperature too when it's 108° which would take away from energy available for physical activity. Isn't that how the old wives tale, feed a fever, starve a cold started? If you push yourself beyond the point where your body can regulate your core temperature you suffer heat exhaustion or heat stroke. It makes sense that your skin temperature would be higher in higher air temperatures and heat loss would be more difficult, especially when the air temperature is higher than the core body temperature. I personally would not like to run in 108°... even for 3 miles.

I think the article about the basketball player suffering from cramps had some good points about how heat affects the body. The point about people with larger body mass overheat more quickly than people with smaller body mass because their ratio of surface area to body mass is less. Smaller people have higher ratio of skin area to body mass so heat dissipates more efficiently.

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The body would definitely divert blood, which is then blood that is not available to deliver oxygen to working muscles. This seems to be a well established fact.

The interesting thing is that it's not core temperature but the difference between core temperature and skin temperature that makes the difference. That may also make sense, though. The body's top priority is to keep the core stabilized. Our skin temperature is normally cooler but, as we produce or absorb too much heat, the skin is going to be the first place to warm up. Our bodies are going to try to push that heat to the skin to be dissipated in order to maintain a stable core temperature.

Body mass to surface area is critical in terms of heat dissipation. I recall hearing that Paula Radcliffe had a disadvantage in the Athens Olympics because she was bigger than the typical elite marathoner. It makes sense. She performed her best in cool, spring and fall marathons. Of course, there are other factors such as male pacers some would suggest played a key role and I wouldn't dismiss those factors. That said, one of the advantages we hear of that the Kenyans have is legs (and arms) that are long relative to the size of the rest of their bodies and quite skinny. These, among other benefits, create a larger surface area relative to body mass and better ability to dissipate heat.

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