Change in pace as a continuous measure
To assess the sensitivity of categorizing finishing time and percentage slowing, we conducted regression analyses. Men and women slowed differentially (F2,91925 = 993, P < 0.0001), so that the sex difference widened among slower runners (adjusted for women relative to men by 12%). For instance, percentage slowing for a 3 h 00 min male finisher and 3 h 26 min female finisher (compared because of the 12% adjustment for finishing time) were 6.9% and 5.5%, respectively (25% difference). However, for a 5 h 00 min male finisher and a 5 h 36 min female finisher (12% adjusted), slowing widened to 18.8% and 14.5%, respectively (30% difference). This regression model explained 20% (R2 = 0.197) of the variation in percentage change in pace, but the relations were not strictly linear.
To examine the nonlinear relation more fully, Figure 4A illustrates a locally weighted (LOESS smoother) plot relating finishing times with percentage change in pace for the entire sample. A scatter plot consisting of a random sample of 5000 finishers has been superimposed onto the figure to add context to these regression fits. Percentage slowing increases more rapidly in men than in women as finishing time increases.
Sensitivity analysis for the 12% adjustment
We next investigated whether our results were sensitive to the 12% adjustment we made to women’s performances. Figure 4B displays locally weighted plots relating finishing times to change in pace for the entire sample using no adjustment, 10% adjustment, and 16% adjustment. No adjustment produced a larger estimate of the sex difference in pacing than that when using adjustment (10% or 16%). Furthermore, the sex difference in pacing was smaller with the 16% adjustment than with the 12% adjustment used in our earlier analyses (Fig. 4A). Nonetheless, even with 16% adjustment, the sex difference in pacing remained apparent in all analyses as noncoincident regression lines (i.e., regression lines of women generally indicating less slowing for any given finishing time).
Finally, we explored the effect of experience on pacing in a subgroup of 2929 runners. These runners had a mean finishing time of 4 h 36 min and included 42.8% female participants. The overall mean ± SD percentage change in pace was 15.0% ± 13.5%. As with the entire sample, men’s percentage change in pace was greater than the women’s (16.8% vs 12.5%; P < 0.0001). Similar to the entire sample, 12.4% of the racers showed marked slowing, with men showing higher frequency than women (16.7% vs 6.6% respectively, P < 0.0001).
The next step was assessing which experience variables were significantly related to uneven pacing. We found greater slowing among those individuals with their earliest recorded race after 2008 (≤3 yr of experience) (ρ = 0.08, P < 0.001), those with fewer previous marathons (ρ = −0.08, P < 0.001), and those with fewer total races at all distances (ρ = −0.07, P < 0.001). There was also greater pace slowing among those whose fastest previous marathons were slower (ρ = 0.19, P < 0.001, in 1856 participants that ran more than one marathon).
Consistent with the findings with the entire data set, the relation of the 12% adjusted finish time and percentage slowing differed between men and women (test for coincidence, F2,2925 = 38.6; P < 0.001). This model explained 20% of the variation in changes in pacing (R2 = 0.197). With the addition of participant age and the experience variables of total number of previous marathons and recent introduction to marathons (≤3 yr of experience), r2 increased to 20.8% (n = 2910, R2 = 0.208). There was no evidence that the experience variables affected pacing differently in men and women (F2,2901 = 2.06, P = 0.13). In a final model, consisting of the 12% adjusted finishing time, age, total marathons run, recent introduction to the marathon, and sex (the main effects of sex and its interaction with finishing time), the coefficients of partial determinations were as follows: 17.7%, 0.1%, <0.1%, <0.1%, and 2.9%, respectively. Thus, finishing time and the differences between men and women explained the largest percentages of the variation in the change in pace. The estimated percentage point differences in pace change, men relative to women, for relative finish times of 2 h 30 min (i.e., female finish time of 2 h 48 min), 3 h 00 min, and 5 h 00 min were 1.6 (P = 0.15), 2.2 (P = 0.001), and 4.7 (P < 0.001) percentage points after adjusting for these experience variables.
This study shows that the sex difference in marathon pacing among nonelite runners is robust in several respects. First, the sex difference was significant in all 14 marathons in our sample. These marathons differed considerably in their size and extent of slowing (Table 1), indicating that the sex difference occurs generally. Second, we showed that, although age (i.e., being an older runner) and faster performances are associated with more even pacing (26), the sex difference generally persists across ages and abilities. There was evidence, however, for an interaction, with a less pronounced sex difference among faster runners. Third, we demonstrated that adjusting women’s performances by 12%—to address men’s greater V˙O2max—does not eliminate the sex difference in pacing. Fourth, we found that, although inexperience is associated with greater pace slowing, controlling for experience does not eliminate the sex difference. Finally, our study is notable in its exploration of pace slowing as both a continuous and a categorical variable. Thus, rather than merely stating that men slowed more than women on average, we showed that, after controlling for age and ability and making the 12% adjustment, women had approximately one-third the odds as men to experience marked slowing (running the second half of the race more than 30% slower than the first half).
Besides demonstrating the robustness of the sex difference in pacing, our study yielded other notable results. One finding is that, making a 12% adjustment to women’s performances did affect the magnitude of the sex difference in pacing. In particular, the sex difference was larger without an adjustment, indicating that previous studies that did not make an adjustment may have overestimated the sex difference in pacing (26,35). Nonetheless, even with the 12% adjustment, evidence for the sex difference in pacing remained reliable. We also showed that although the estimated sex difference in pacing is generally insensitive to the exact adjustment used (between 10% and 16%), the sex difference in pacing decreases as the adjustment increases.
Our study also provided the first results directly bearing on the hypothesis that experience is related to pacing in the marathon (26). We showed that four experience variables were significantly associated with pacing, namely, years of experience, previous marathons, previous races at all distances, and fastest previous marathon. Thus, more experienced runners paced more evenly and inexperience was associated with greater pace slowing. Moreover, at least two of the experience variables (total marathon run and recent introduction to the marathon) explained variation in pacing independent of the effects of age, finishing time, and sex. The amount of variation explained by the experience variables, however, was modest (>0.1% for each) compared with sex (2.9%) and finishing time (17.7%). Consequently, controlling for experience does not eliminate the sex difference.
What causes the sex difference in pacing?
Various physiological factors might contribute to the sex difference in marathon pacing, although we did not measure these. For example, men are more susceptible to muscle glycogen depletion, which can contribute to greater fatigability and “hitting the wall” or dramatic marathon slowing (4,9,30,33). Men may be more susceptible to slowing because, during endurance exercise, women generally have a lower RER, indicating that they use proportionately more fat and less CHO at a given intensity of exercise (7,25,34,36). In general, women possess larger proportional areas of Type I muscle fibers, which are more resistant to fatigue especially for long-duration exercise (19). Supporting this hypothesis are studies finding that men are more likely than women to report dramatic slowing or hitting the wall (4,33).
Another possibility is that men might be more susceptible to hyperthermia (35), which is believed to be another frequent contributor to marathon slowing (16,27). Supporting this is the finding that the sex difference in marathon pacing in nonelites was larger in the 2007 Chicago marathon, which was hot (27°C), than that in the 2009 Chicago marathon, which was cool (3°C) (35). Challenging this hypothesis, however, are studies indicating that men typically enjoy advantages in thermoregulation (14).
Decision making could also contribute to the sex difference in marathon pacing. Specifically, if men are more likely to adopt a “risky” or competitive pace relative to their ability, this could increase their likelihood of slowing later. This is because a fast pace has numerous physiological consequences, including increasing the risk of hyperthermia and glycogen depletion (3,9,13,37). Evidence for a sex difference in pacing decisions comes from a study showing that marathon performances among nonelites tend to cluster at round numbers (e.g., just under 4 h) because of some runners speeding up in the final 2.2 km of the race; this pattern was substantially more pronounced among men than among women (2). There is also evidence that male distance runners are more likely to adopt a competitive rather than a recreational orientation towards the sport, as follows: 1) more male than female runners report that competition motivates them to run (6,22,29), 2) roughly three times as many men as women run fast relative to sex-specific world-class standards, and this may reflect that that more men engage in the training necessary for faster performances (11), and 3) when men and women have the option of entering a single-sex competitive road race or a single-sex noncompetitive road race, men are more likely than women to select the competitive race (15). In addition, there is much evidence for sex differences in risk taking in other contexts, including health, recreation, and finance (5,10,18).
Does the sex difference narrow among faster runners?
Another interesting question is whether the sex difference in pacing is less among faster runners. Addressing this question is important because it could provide clues about the cause(s) of the sex difference. Within financial domains, for example, studies report that the sex difference in risk taking substantially weakens or disappears when financial knowledge is controlled (12,17,23).
In the present study, despite the large overall sample size, there were very little data on genuinely elite or even near-elite runners. Moreover, faster runners, both men and women, generally maintain even paces (Table 2 and Fig. 4A). Notwithstanding these considerations, we did have some relevant results, although they provide an ambiguous answer to the question of whether the sex difference in pacing narrows among faster runners. On the one hand, the sex difference in pacing occurred among all finishing time groups (Table 2 and Fig. 1), and among runners in our two fastest groups (men running faster than 3:00 or 3:30; women running faster than 3:22 or 3:55), the magnitude of the sex difference based on categorical variables (i.e., OR) was similar to the sex difference across all finishing time groups (Table 2 and Fig. 1). On the other hand, when using continuous measures, the significant interaction of sex with adjusted finishing time indicates that the sex effect was significantly less pronounced in faster runners (Fig. 4A). Specifically, we estimated that among faster runners (3 h 00 min male finisher and corresponding 3 h 26 min female finisher), men slowed, on average, 25% more than women, whereas among slower runners (5 h 00 min male finisher and corresponding 5 h 36 min female finisher), men slowed, on average, 30% more than women.
We note that there have been several studies on pacing among elite men and women in other endurance sports. These typically indicate no pacing differences (28) or else subtle differences that are difficult to interpret because of sex-specific aspects of the competition, such as the depth of competitors (37).
Are women more effective pacers?
There is consensus that even (or nearly even) pacing is best for optimizing performance in races that take several hours to complete, such as marathons (1). Furthermore, dramatic pace slowing in a marathon is associated with considerable discomfort (4,33). Our results therefore imply that women are generally more effective than men in their marathon pacing. Nonetheless, this conclusion should be considered provisional because an evenly paced race does not automatically indicate a well-paced one. This is because an individual may be overly conservative given their training and ability. Similarly, although dramatic slowing in a race almost certainly indicates a poor outcome for that race, a risky initial pace may be desirable in a broader context. For instance, if a runner’s goal is to achieve at least one exceptional performance during the year (e.g., setting a personal record, winning their age group), he/she may have the best chance of achieving it if he/she often begin his/her races with a fast risky pace. Thus, a definitive answer to the question of whether particular groups or individuals are better pacers requires comprehensive assessment of goals.
Insights from nonelites
Much has been gained from studying the pacing of elite and subelite endurance athletes (1), and investigating the pacing of nonelite or recreational athletes may provide further insights. For example, besides sex difference, our study confirms that older runners and runners with faster initial pace tend to pace more evenly (26) and, to our knowledge, none of these effects were predicted by studies on elite pacing. Moreover, the variation in pacing among nonelites shown in our study (Fig. 4A) seems far greater than that among elites (13). This is probably due to the tremendous diversity of nonelites’ goals, training, and abilities (2,11). We suggest that future studies of pacing in nonelites assess these factors and others (e.g., coaching, fluid and CHO ingestion, use of pace groups, and targeted pace) to illuminate the interactions among physiological and psychological factors in pacing. This research would seem of interest to many scientists and perhaps also to the public. For example, although marathon training handbooks, magazines, and Web sites generally contain sound advice, their discussions of pacing might be improved considerably as the factors related to uneven pacing are identified.
The current study is not without limitations. First, we evaluated pacing only by assessing first and second half split times, so we were unable to model when the slowing typically began. Other studies indicate that slowing becomes pronounced in the final 10–15 km of the marathon (4,13,26). Second, we did not account for pacing variation associated with race courses or weather conditions and this variation may be substantial (13,35). Third, although we succeeded in identifying experience factors associated with pacing variation, other experience factors that we did not assess may also be important. Similarly, as noted previously, we had no individual data on other relevant factors, including training, CHO ingestion, and targeted pace. Fourth, some runners may have participated in more than one race in our sample. We were unable to “cluster” performances under a given participant, and this could have led to CI values being smaller than they would have been if clustering was modeled explicitly.
This study demonstrates that the sex difference in pacing among nonelite marathon runners is robust and greater among slower runners. It occurs consistently across marathons, persists across age groups and ability levels, and remains when experience is controlled and when women’s performances are adjusted to address men’s greater V˙O2max. The causes of the sex difference in pacing are presently unknown, but they likely involve the interplay of physiological and psychological factors. Studying this sex difference and related pacing phenomena should yield performance insights for scientists, coaches, and athletes.
This publication was partially supported by grant number UL1 TR000135 from the National Center for Advancing Translational Sciences. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health.
The authors thank Tyler Esser, Joseph Fleming, Alyssa Stevens, Jonathon Senefeld, and Marissa Miars for their assistance with data collection.
The authors declare no conflict of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:© 2015 American College of Sports Medicine
GENDER; DISTANCE RUNNING; RISK TAKING; ENDURANCE EXERCISE; EXPERIENCE; SUBSTRATE USE