Despite the recent success of ultra endurance running, the physiological consequences of ultramarathons are quite poorly understood. Neuromuscular Consequences of an Extreme Mountain Ultra-Marathon presents the first scientific study of the physiological consequences of The North Face Ultra-Trail du Mont-Blanc (UTMB). This race around the Mont Blanc Massif through three countries (France, Italy, Switzerland) has been organised in every August since 2003. This study was done in 2009 UTMB.
This popular 166 km mountain ultramarathon with 9500 meters of positive and negative elevation change has previously accepted about 2500 participants (down to 2300 for this year) from a much larger group of interested runners (in 2010, 45% of the qualified applicants were not accepted). 22 male runners participated in this study. 34 subjects were initially recruited but only 22 (65%) were able to complete the race (within the 46 h overall time limit) and take part in the first part of the study (fatigue). This ratio about the same as the overall ratio of finishers in UTMB. All the subjects were experienced ultramarathon runners, which is a required by the race organisation in order to qualify to submit their application. On average, the subjects had 13 years of training history in running and 5 years of ultra endurance experience. Eleven of the 22 subjects participated in the second part of the study (recovery).
The average finishing time of the subjects was 37 h 37 min. All levels of performance were represented in the group of subjects as shown by their rank ranging from 5th to 1380th place (of 1384 finishers). Poles were used by 95% of the subjects during uphills and 86% in dowhills.
Large maximal voluntary contraction decreases occurred after UTMB: −35% for knee extensors (KE) and −39% for plantar flexors (PF). Significant modifications in markers of muscle damage and inflammation were observed after UTMB as suggested by the large changes in creatine kinase, myoglobin, and C-Reactive Protein. Moderate to large reductions in maximal compound muscle action potential amplitude, high-frequency doublet force, and low frequency fatigue (index of excitation-contraction coupling alteration) were also observed. Sixteen days after UTMB, neuromuscular fatigue had returned to initial values, with most of the recovery process occurring within nine days of the race. Regarding body mass, the subjects lost about one kg during UTMB.
Although the amplitude of central drive reduction was lower for PF muscles than for KE, there was a significant correlation between changes for both. This result could reflect the existence of a common central safety mechanism (this refers to the famous Central Governor Model developed by Tim Noakes) aimed at reducing neural input to working muscles to limit fatigue and damage.
Interestingly, hyponatremia and hypoglycaemia were not observed among these subjects, so fatigue was not caused by them. Hyponatremia has been previously reported in prolonged running, probably because runners have been recently encouraged to overdrink during races. Two factors could explain why this was not the case in the present race: (i) temperature was not as high as in other famous ultra-marathons like the Comrades or the Western States 100 miles thus runners probably did not drink as much and (ii) warm salted soups are served at every aid station and are usually appreciated by runners.
No significant correlations were found between global fatigue or peripheral alterations and age, level of performance or running experience.
This study is the first to detect the existence of low-frequency fatigue after prolonged running, likely due to the 9500 m of negative change in altitude (ie. downhills). Most of the uphills were actually performed walking during UTMB. For this type of locomotion, the major change due to slope is a greater contribution of hip extensors, a muscle group not studied in the present experiment. In addition, it is likely that the use of poles modifies the relative contribution of different muscle groups.
As expected, UTMB induced large effects on blood markers of muscle damage and inflammation. Of particular interest is the large variability among subjects in these responses, e.g. in CK activity. The comparison of these different markers with the literature shows that UTMB was extremely taxing. UTMB activity levels are similar to those measured in patients undergoing severe rhabdomyolysis, but very rarely led to hospitalization of runners. One exception was noted in UTMB 2008, when one subject went to an intensive care unit for dialysis. It was eventually found that extreme exercise was combined with the use of nonsteroidal anti-inflammatory drugs the week preceding the race and dehydration due to diarrhea. The two subjects with extremely high CK values did not have particular health troubles. The incidence of hospitalization may thus be secondary to inappropriate use of pharmaceutical.
The markers of muscle damage and inflammation in the present study were lower than those consistently observed after Spartathlon (a 246 km road ultramarathon in Greece). In fact, while finishing times are similar for both Spartathlon and UTMB, higher concentrations of LDH, CK, CRP and total white blood cells have been reported after the Spartathlon compared with the present findings. It is hypothesized that the combination of harder road surface and higher external temperature for Spartathlon could explain these observations.
As early as two weeks after such an extreme running event, maximal force capacities have returned to baseline but it is likely that neuromuscular measurements do not fully describe the recovery process of an athlete. It is interesting to note that while subjective pain was lower for PF, the slope of recovery for this variable was lower than for KE, suggesting long-lasting damage.