The aim of our study was to evaluate the influence of running an ultramarathon over a distance of 100 miles on the heart rate and the HRV, as well as the potential use of these parameters to predict full recovery following this exertion to full physical capacity.
The interpretation of HR and HRV in the context of endurance sports is still a controversial topic. While, Fazackerley et al. (3) report an increase in heart rate accompanied by decreased in HRV parameters one day after completing a 64 km run, Pichot et al. demonstrated an increase in HRV indices after a one-week period of over-training in non-athletes (5). Another study of two elite triathletes by Plews et al. (6) reported even a decrease both in HR and HRV following exertion to full physical capacity. The last finding being thought to be due to a maximum vagal activity, with the results of a limited modulation capacity of the HRV parameters (7) due to already saturated acetylcholine receptors.
In addition, Schmitt et al. showed on the French national skiing team that in periods of physical fatigue, a decrease in the HRV parameters is recorded. (8)
In consistency with published data, the presented study found an increase in the heart rate during the first hours after the UM (U2). This is commonly accepted to be due to a shift of the autonomic nervous system in favour of sympathetic activity (9, 10). This sympathetic dominance leads to a decline in the HRV indices, especially the SDNN value, which describes the cooperation between the sympathetic and parasympathetic nerves (11, 12) and is consistent with our data.
Yet, the main finding of the current study is shown in the comparison of the parameters of autonomic nervous system seven days before the run (U1) with the measurements seven days after the run (U3). While the baseline heart rate at U1 did not show significant differences to the measurements at U3, it can be seen that there is still no full return to baseline of the HRV at (U3), shown by lower average values for the SDNN, RMSSD and pNN50 (graphs 1–4). First of all, these findings suggest that the athletes did not fully recover from the exertion even 7 days after the 100 miles. Second, in terms of recovery after a 100 miles run, HRV seems to be more accurate in the prediction of recovery, than the absolute heart rate. Although these findings stand in contrast to the findings of Fazackerley et al., whose runners achieved a return of HRV to baseline within two days after 64 km run, this difference might be explained by the shorter distance covered by the athlete`s reported in the Fazackerley study.
Although the HR and HRV seem to be useful to evaluate recovery after such an extreme exertion, neither the baseline HR, nor the baseline HRV seem to predict the finishing time.
When analyzing data for influencing factors on finishing times, the presented data did only show the age as a decisive factor
Because of the low number of participants in this study, the following might only be speculated. The low RMSSD mean of non-finishers, which is also referred to as the body's rate of recovery (1, 13) might be interpreted as a better ability of the finishers to regenerate in advance. The fact that RMSSD in U3 was higher in the non- finishers than in the finishers is probably justified with the considerably lower running distance covered by the non- finishers (Table 3).
The presented data imply that none of the parameters predicting post- exertional recovery can be used to predict finishing times or the ability to finish an ultramarathon as such. It can only be speculated that there are not only physiological factors influence the finishing of an ultra-marathon, but also psychological and environmental factors that mainly influence the coping with such a large distance.