Michael J. Joyner
Thursday April 28th, 2016

About a week before the Boston Marathon I got pinged on Twitter by a sub-elite runner named Steve Sprieser who was worried that weather at this year’s Boston would be hot. Steve’s worries turned out to be true and the winning times were relatively slow this year: 2:12 for the men and 2:29 for the women.  

From what I could glean, Sprieser had been training in cool temperatures in the Midwest and was not ready for the heat. His goal was to run the marathon in 2:35. With only a week to go he did not have a lot of time to adapt, so I asked my colleague and thermoregulation expert Dr. Chris Minson at the University of Oregon for input about the best short term strategy for Sprieser, who ended up finishing in 2:37:30 and place 84th among the men. This is a fine performance and especially notable in the heat. Based on Sprieser’s success—he ran a great race in the heat and even nailed even splits throughout—I thought it might be a good idea to share Dr. Minson’s advice.

Dr. Michael Joyner: Chris, can you briefly summarize the 140 character insights you shared with Steve on Twitter about how to get ready for a hot Boston with only a week to go?

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Dr. Chris Minson: One of Steve’s concerns was about the wind, with an expected tailwind of about 10 mph. At his planned pace of 2:35, he was concerned there would be little to no cooling benefit on a day that was warmer than where he had been training in Chicago. So I suggested that a couple easy runs in a hot room over the few days before the race could help. Steve needed to keep it easy; get hot and watch his hydration status. I also suggested that overdressing might help and that he consider adding one more layer to get body temp up. The other important point was in terms of fluid replacement: in the short run leading up to a race, don’t change from what you’ve been doing as it’s too risky for GI problems. Steve subsequently reported that very few runners seemed to be acclimated well to the heat, and that the pack he was running with diminished quickly after the first 8-12 miles.

MJ: If someone had more time and was thinking about getting ready for a marathon or other endurance even in a hot environment, how long does it take to get fully adapted?

CM: Ideally 10-14 sessions of heat exposure will result in the best performance benefits, getting body core temperature raised for 60-100 minutes each session. There are shorter heat acclimation protocols, but full adaptation takes more than seven days. The goal is to simulate worst-case race conditions, and be careful not to let the heat acclimation sessions derail the training plan.

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MJ: Your lab has shown that training in the heat can help performance in a cool environment.  How does that work? Is this the new altitude training? 

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CM: This is currently a hot topic (pun intended) and with any new approach there is some degree of controversy. We have shown that using heat acclimation in the same manner as the “live high, train low” approach can improve performance in a cool environment. That is, separating the acclimation sessions from the high-intensity workouts. This can be done by performing easier days in the heat, sitting in a hot tub sauna post-training or doing some heat exposures during the taper. The main mechanism is likely through having an earlier rise in skin blood flow and sweating, helping to keep core temperature low. Even in relatively cool environments, body core temperature increases resulting in a competition for blood flow (and therefore oxygen delivery) between the skin and the muscle. Short-term heat acclimation should increase plasma volume somewhat, and from our data may result in a higher maximal cardiac output.

MJ: Have any elite athletes tried this yet?

CM: We have worked with a few elite athletes in the past, and have consulted with many more. Most were using heat acclimation in case the competition day was hotter than they were trained for. There are some professional teams, particularly in other countries, which have employed this approach. However, I have not seen any data or circumstances where being acclimated for the heat resulted in a detriment in performance in any environment. Thus it is a good approach when done correctly and may improve performance even in a temperate environment.

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MJ: Exercise in the heat can be very dangerous. How do both novices and elite athletes manage that danger? Are there any big “don’ts” from your perspective?

CM: The risk is to overdo the heating, especially when first starting out. A notable accident occurred in 2012 when a well-known ultrarunner named Michael Popov died when doing a six-mile training run in 120-degree heat in Death Valley near the Badwater course. He was heat acclimated and should have been able to handle this short of a run. He was alone, which in this type of heat is a big “don’t.” For heat training runs, people should try to work out together, be in a place they can be reached, be prepared with enough fluids, and have a way to communicate with others, via a cell phone with service or a GPS emergency device.

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MJ: What is the minimum heat acclimation an athlete can do?

CM: Like Steve, if you wait until the last few days before an event, one has to be very careful to not do anything that could cause fatigue or to negatively impact performance. However, there are a lot of athletes now using “short-term heat acclimation” protocols. These are typically only 3-5 days long. The goal is to lessen the effects of the heat on performance, even though full acclimation is not possible. The data suggests this is effective in lowering exercise heart rate, body core temperature riseand perception of effort, key factors for exercising in the heat that affect performance.

Michael Joyner, is an expert in human performance at the Mayo Clinic, these views are his own.  You can follow him on twitter @DrMJoyner. 

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