Pain threshold
On average, runners reported pain starting between mile 15 and 16 of the marathon. However, there was substantial variability in the onset of pain during a marathon, ranging from within the first mile to the last mile of the race. Substantial inter-individual variability characterizes pain threshold measures even when standardized noxious stimuli are presented to a homogeneous group in a lab setting, including pressure, thermal and cycling exercise stimuli (7, 8). Thus, it was not surprising that there was substantial variability in the mile at which pain was first experienced during a marathon run, especially given that the absolute exercise stimulus was not the same for every participant because of variations in, for example, race course elevation.
Pain location
The fact that pain was experienced most frequently in the thigh, hamstring and calf muscle groups is consistent with prior reports of hamstring and calf injuries among marathon runners (9). The hypothesis that most runners (> 50%) would experience pain during the marathon was confirmed. Indeed, only 2 of 1251 runners reported feeling no pain during a marathon. These data indirectly support the idea that pain is not a primary constraint on human endurance performance (10). For example, ultramarathon runners can continue to endure for 100 or more miles per day despite the presence of pain (11). It may be possible for a higher percentage of participants to run a pain-free marathon if they are well trained for the task, if they take strategic walking breaks and if a key goal is to run at a pace that avoids pain. It is unknown how many people who participate in a marathon, run with a primary goal to avoid pain. The motivations for running were not assessed among the participants in the present study. Individuals train for and run marathons for a host of reasons, including to lose weight, to increase physical fitness, to give life meaning, to help cope with life’s problems, to socialize, to achieve a goal and others (12, 13). Certain types of goal achievement motivations, such as running a fast time, are inconsistent with avoiding pain.
Hypothesis of moderate intensity pain for most runners
The hypothesis that most people would experience moderate intensity pain during the marathon was not confirmed. The average pain intensity at the primary location of pain represented pain that was “strong”; that is, more intense than moderate but less than the highest intensity pain ever experienced which in this study approached the extremely intense category of the 0–10 scale used. About two thirds of the sample reported overall pain that ranged from 3 (moderate) to 7 (very strong). One of the few prior studies that measured pain associated with marathon running queried 127 participants in a marathon in Kraków, Poland and found that recalled pain intensity of the marathon one week or one month after the marathon averaged between 5 and 6 on an 11-point numerical scale (14). These observations are generally consistent the present findings. The prior study manipulated the timing of the recall post-marathon and compared participants who were, and were not, experiencing pain during the recall period. The authors concluded that pain intensity experienced during a marathon run is underestimated one month after the marathon compared to a week after, and is mediated by the pain experienced when the recall is made (14). No direct comparison can be made between this prior smaller study and the present larger study because of methodological and study aim differences. In the present study, however, the presence or absence of pain during the recall was not obtained and the time since the last marathon varied. The time since the last marathon was measured in the present study and removing the influence of that variable did not significantly change the strength of associations based on partial correlation analyses.
Hypothesized correlates of pain intensity during a marathon
It is not surprising that, as hypothesized, the intensity of pain during training and the percentage of training days in pain were significantly related to pain during the marathon because whatever caused the pain during training, such as an injury, hilly training routes or simply high intensity effort, could have carried over to race day. Other plausible variables that could account for the pain intensity experienced during a marathon run, beyond running-related variables such as prior aerobic training (15), physical fitness (16), injury status (17), the intensity of effort (18) and the extent to which the marathon course had elevation changes, include genetics (19), family history of hypertension (20), typical sleep duration (21), health status and biological sex.
It is unclear why the average pain intensity during the marathon was positively correlated with the highest intensity pain ever experienced. While speculation about masochistic and addictive elements of long distance running are perhaps relevant (22), future research is needed to understand this finding. Possible explanations for the negative correlation between the number of prior marathon runs and pain during the marathon appear more straight forward. Multiple psychophysiological adaptations from training for, and competing in, marathon runs serve to reduce pain and effort perceptions associated with the marathon (23).
Not surprisingly, and as hypothesized, effort ratings were positively correlated with the average pain intensity experienced during the marathon run (r = .11) and the magnitude of the relationship was higher after controlling for run time (r12.3=.18). Pain and effort are conceptually and empirically positively related; exerting more effort results in running faster which increases the likelihood of higher intensity pain. The magnitude of these relationships, however, can be influenced by a host of variables including whether one is running uphill or downhill (24), recent prior run training (25), exercise duration (26) and health status (27). Most of the available data about pain and perceived effort during exercise comes from studies of indoor cycling. Thus, the present study adds novel data to the small literature on pain, effort and marathon running.
Hypothesized sex-related differences
On average, females did report higher average pain intensity at the primary location of their pain sooner in the race than males by an average of 0.3 raw pain score units, however, the magnitude of this difference was not enough to support the hypothesized sex-related difference in this variable even after adjusting for the sex-related difference in effort. The observation of lower effort ratings, on average, for the female sample compared to the males is consistent with prior studies showing that females often exercise at a lower intensity than males and more frequently engage in physical activity modes that are less strenuous (28, 29). In marathon running, however, women maintain a steady pace to a greater extent than men and this plausibly could contribute to lower effort ratings, though the reason for this sex-related difference is unknown (30).
Limitations
Like all research, this investigation had limitations. The study was not controlled in a way that each runner ran the same course; consequently, error variance in estimating pain intensity during the marathon potentially was increased because of differences in the courses run. The survey was not a random sample from a well-defined population of marathon runners. Therefore, the findings may not generalize to other samples of marathon runners. Nonetheless, the findings contribute to the literature because the participants ran in over 250 different marathons and no similar data exist. Comparisons between females and males were imperfect because they were not based on samples carefully matched to avoid confounding variables such as the course run, prior training, running speed and many other variables that could have influenced pain intensity.