The main findings of the present study were that (i) women had larger total pace range than men, (ii) the smallest total pace range was in the 3-4 h group and the largest in the 10-11 h group, (iii) the smallest total pace range was in the older age groups, and (iv) smaller differences among age groups were found in the faster performance groups.
The more even pacing observed in the older age groups was partially in agreement with previous studies on running. In 100-km ultra-marathon running, no differences in pacing among age groups was shown [12]. On the other hand, a more even pacing was found in older runners in the ‘New York City Marathon’ [13]. The smaller differences among age groups observed in the faster performance group was a novel finding as no previous study had ever examined the age×performance interaction on pacing in XC skiing.
We might assume that master XC skiers would exhibit different performance characteristics than their younger counterparts since aerobic capacity, which is a main determinant of performance in XC skiing [14], declines with aging [15]. A study that modelled changes in the criterion measure of aerobic capacity, i.e. maximal oxygen uptake (VO2max), identified age, fat-free mass and exercise training status as predictors of VO2max [16]. Nevertheless, the decline of aerobic capacity with aging might be attenuated when large training volume is maintained in the master athletes [15, 17] and healthy adults [18]. Also, exercise might attenuate the decline of motor and cognitive abilities with aging [19]. Furthermore, it has been shown that the decline in VO2max was proportional to the decline in training volume in endurance trained men [20]. Thus, the abovementioned long-term exercise-induced adaptations of aerobic capacity might consist in the physiological mechanism which attenuated the decline of performance with aging and explained why both younger and older fast XC skiers adopted similar pacing strategies.
In addition, the total, positive and negative pace range were smaller in the performance groups with fastest race time indicating that the faster performance groups adopted a more even pacing. This observation was in agreement with previous research [8] indicating that XC skiing presents similar trends of the relationship between performance and pacing as those observed in other endurance sports.
An unexpected result was that men showed a more even pacing than women, since research on endurance sports such as the ‘Chicago Marathon’ [21] and 100-km running [22] had previously suggested women as better pacers. This disagreement in the sex difference in pacing among endurance sports might be due to unique characteristics of XC skiing, where human body interacts with sophisticated equipment and there are increased demands in upper body muscle power compared to other running or cycling [23, 24]. In addition, the more even pacing in men observed in the present study was in contrast with a previous study on a small sample of finishers in the ‘Vasaloppet’, where women showed a more even pacing profile than men with the same finish time, start group, age, and race experience, and men were faster in the first half and women were faster in the second half of the race [4].
The results of the present study are limited by the unique characteristics of the ‘Vasaloppet’ in terms of race distance and change of elevation; therefore, they should be interpreted with caution when comparing with other XC races. Also, a unique characteristic of this study was the use of pace range to study pacing, which was a recently developed methodological approach [10]. Although this approach provided a reasonable estimate of pacing, as it identified accurately the slowest and fastest splits and the deviation (%) of their speed from the average race speed, the findings should not be compared to studies using other methodological approaches (e.g. coefficient of variation [25], % change of speed between consecutive splits [13]). Moreover, the findings were based on comparison among different sex, age and performance groups and, consequently, did not establish a causal relationship of sex, age and performance with pacing.
Nonetheless, strength of the study was the inclusion of all editions of the ‘Vasaloppet’ (2012–2017) for which all split times and finishers’ age were available resulting in one of the largest sample of XC skiers ever studied. The large number of finishers allowed drawing safe conclusions about differences in pacing by sex, age and performance group. It should be highlighted that the large sample size should be accounted for the statistically significant findings (e.g. at p < 0.001) in cases of trivial magnitude of differences; thus, both statistics (i.e. p value and effect size) should be considered in the interpretation of the findings. Furthermore, we highlighted unique pacing patterns in XC skiing which differ from other endurance sports such as the sex effect on pacing. Men XC skiers have a more even pacing than women which is in contrast with the sex trends in pacing in other endurance sports (e.g. running) that suggest women as better pacers. In XC skiing, the sex difference in pacing seems performance-dependent with men showing more even pacing than women in all performance groups, except the slowest.
Considering the large number of master XC skiers, the findings of the present study would be of practical importance for coaches and fitness trainers in this sport in order to adapt the training and competition practice such as pacing, which was previously established in younger XC skiers, in the specific demands of the master XC skiers. Fast master XC skiers should be advised adopting a similar pacing strategy as their younger counterparts. Older XC skiers should be expected to show a more even pacing than their younger counterparts. A trend of a relatively even pacing in both slow and fast older XC skiers compared to their younger counterparts should be taken into account by coaches and fitness trainers during the training practice and the preparation for a race such as ‘Vasaloppet’. By definition, pacing refers to the management of effort [6] or energy expenditure [7] during an exercise; thus, the variation of pacing by age might provide practical information for master athletes to optimize performance. The role of pacing is even more pronounced in the case of XC skiing, which is an ultra-endurance sport (i.e. race time longer than 6 h for most master finishers).