Abstract
Objective
Weight loss during ultramarathon competition is often considered a useful predictor of performance, hydration status, and hyponatremia. The validity of this assumption has not been well studied. This study was designed examine the correlation between weight change and performance, urinalysis, and serum sodium in a 161-km ultramarathon.
Methods
Runners were weighed at pre-race check-in, at the half-way point, and at the finish line. Height was self-reported at prerace check-in. Willing finishers underwent urinalysis and provided a blood sample for serum sodium analysis.
Results
Out of 672 runners who started the race, 351 (52%) successfully completed the race under the 30-hour cut-off time. Weight was measured on 658, 518, and 344 runners at prerace, halfway, and finish line, respectively. Urinalysis (dipstick) was done on 70 runners (51 finishers), and blood samples were obtained from 84 runners (66 finishers). Mean (± SD) weight and BMI (body mass index) were 73.1 ± 10.3 kg and 23.3 ± 2.3 kg/m2, respectively. Mean weight change for runners was –2.1 ± 2.1% and –0.84 ± 2.3% of their prerace weight at midpoint and finish line, respectively. Based on linear regression analysis, there was a significant correlation between percentage weight change from prerace to finish line and finish time (P = .016, r 2 = .02). There was no statistically significant relationship between weight loss and urine specific gravity (P = .124, r 2 = .05), or between weight loss and serum sodium concentration (P = .183, r 2 = .03).
Conclusions
Significant weight fluctuation is common during ultramarathons. Our data show that weight change may be a weak predictor of race performance and that faster finish times tend to occur with more weight loss. Weight change is not a useful predictor of urine specific gravity, nor is it useful as a predictor of serum sodium. More study is needed to determine if weight change during an ultramarathon is correlated with adverse patient outcomes.
Funded in part by the ACSM Clinical Sports Medicine Endowment Grant.