Active Voice: The Tortoise and the Hare - A Sex Difference in Marathon Pacing

By Robert O. Deaner, Ph.D. and Sandra K. Hunter, Ph.D., FACSM

Robert O. Deaner, Ph.D. Sandra K. Hunter, Ph.D.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

Robert O. Deaner, Ph.D., is an associate professor in the Department of Psychology at Grand Valley State University in Allendale, Mich. His overarching goal is to contribute to a scientific understanding of human nature, especially by demonstrating the value of evolutionary theory. Most of his current projects involve sex differences and sports.

Sandra K. Hunter, Ph.D., FACSM, is a professor in the exercise science program with the Department of Physical Therapy at Marquette University in Milwaukee, Wisc. Her research focus includes understanding the mechanisms for (1) sex and age differences in motor control, neuromuscular fatigability and human performance in healthy and clinical populations; and (2) the added effects of stress and exercise training on motor control and fatigability of old adults and clinical populations.

This commentary presents Drs. Deaner’s and Hunter’s views on a topic related to the research report that they and their colleagues recently authored. The report of their original investigation appears in the March 2015 issue of
Medicine & Science in Sport & Exercise® (MSSE).

Distance running is one of the most popular forms of exercise in the U.S. and, for many recreational runners, participating in races is a major motivator. A key aspect of successful racing is selecting an appropriate initial pace, given one’s ability and training. An initial pace that is too slow may not allow a runner to achieve their time goals, but starting too fast may result in pronounced slowing and also great discomfort. Outstanding endurance performances involve almost even pacing. The current marathon world records for men (Dennis Kimetto, Berlin, 2014) and women (Paula Radcliffe, London, 2003), for example, were achieved by running the second half of the race just 30 to 40 seconds faster than the first half. Despite the importance of pacing to all runners, most pacing studies have only considered elite competitors.

In the March 2015 issue of MSSE, we reported our findings from a pacing study based on all finishers at 14 recent U.S. marathons. Collectively, those races included almost 92,000 performances. The strongest predictor of even pacing was overall performance: slower runners were much more likely than faster runners to reduce their speed in the second half of the marathon. Another key predictor of pacing was sex: on average, men ran the second half of the marathon 15.6 percent slower than the first half, whereas women slowed by an average of 11.7 percent. The sex difference was especially clear when considering runners who slowed by 30 percent or more: men were about three times as likely as women to experience such dramatic slowing. Similar effects have been reported by others in one earlier study, which employed a smaller sample.

We also investigated whether racing experience was related to pacing and whether it might contribute to this sex difference. For more than 2,900 runners, we acquired information on racing experience from the web source We found that years of racing experience and number of previous marathons finished were both associated with more even pacing. However, these experience effects were similar for men and women, so that controlling for experience did not eliminate the observed sex difference in marathon pacing. In addition, we showed that, although older runners tended to pace more evenly, the sex difference in pacing held across age groups.

Our results raise many questions, including why men tend to slow their pace more than women do. One possibility is that this reflects men being more likely than women to decide to undertake a risky, aggressive pace. A risky pace may pay off by allowing a runner to achieve a superb performance, but it also increases the risk of dramatic slowing. A second possibility is that physiological factors cause the sex difference in pacing. Women typically use more fat and less carbohydrates during endurance exercise of similar intensity. This should make them less likely to ‘bonk’ or ‘hit the wall’ because they are less likely to have their muscles depleted of glycogen.

To better address the predictors of successful pacing in non-elite runners, we suggest that future studies obtain data on runners’ training, targeted pace, subjective feelings and measures of physiological status. Such studies might go a long way toward clarifying reasons for these sex- related pacing differences, helping runners achieve more even pacing and better performances, and enjoy their racing more.