Impact of Temperature on Running Performance

Everyone who's laced up their shoes for any period of time knows that some temperatures are better than other for running fast. The reason for this is simply energetics: the human body is a bio-organic engine, which generates waste heat (an elite marathoner burns over 1400 calories an hour during a race). We must dissipate this heat. If we don't, certain biochemical processes (notably in the brain and liver) are inhibited and we will tend to slip into comas (a phenomenon somewhat inappropriately called heat stroke). Our bodies dissipate heat predominantly through skin at a rate that depends on many things: surface area vs. body volume, AND the difference between body temperature and air temperature. In warmer weather. Most of us don't think about it, but colder weather also negatively affects us, as our blood vessels must dilate to circulate warm blood to cold hands, forcing our hearts to work harder. This recent study by Ely et al (sponsored by the US Army Research Institute of Environmental Medicine) addresses the former possibility in an analytical study asking just how much do higher temperatures negatively affect running performance in a marathon. To do this, the authors surveyed the finishing times of elite marathoners, as well as the 25th, 50th, 100th, and 300th finisher from various well-known marathons (including New York and Boston) and compared them to the course record (i.e., a 2:10 marathon is 8.3% slower than a 2:00 marathon). Finally, the authors examined these finishes in light of the official temperature conditions recorded at each race, breaking them down into four groups of temperatures:5-10, 10-15, 15-20, and 20-25C (that's roughly 41-50, 51-59, 60-67, and 68-77F). At the elite level, there was a progressive decline as temperature increased (an average of 1.7, 2.5, 3.3, and 4.5% slower than course record on average for each respective temperature category).

Unless your last name is Tergat, I've got some bad news for you: elite runners appear to be less affected by dramatic increases in temperature than the average person. The authors examined the finish times of more pedestrian runners, and found that their performance falloff to be more dramatic as temperature increased. For example: runners coming in 25th saw a slowing of 3.6% from the coolest temperature group to the warmest, very comparable to the 2.8% falloff observed in elite athletes. However, the 300th finisher exhibited a 7.9% falloff in the same conditions. Several possibilities exist for this discrepancy, including (a) a failure of less elite runners to acknowledge the conditions and accordingly modify their effort and/or (b) the existence of a threshold temperature over which performance suffers more dramatically and/or (c) inappropriate modification of hydration/nutrition/warmup strategies in less accomplished runners.

This article is the first I am aware of that quantifies the drop in running performance based on temperature. Overall, I find this to be a solid study with well-grounded statistical analysis and a sufficient sample population to draw conclusions from the data. One thing I would like to see in this study or a future investigation is an analysis of the effect of humidity. Since humans sweat to dissipate heat, drier conditions favor this approach, and I would be willing to wager an even more dramatic performance falloff occurs in high humidity environments. Even better: a comparison of heat, humidity, and elevation change on running performance- all the better to know where to go when looking for a personal record!