Impact of Running a 162-km Mountain Race on Hydration and Gastrointestinal Response

Gastrointestinal (GI) distress is a common complaint among runners, often worsening when less hydrated. PURPOSE: The purpose of this study is to evaluate hydration status and GI responses of 162-km ultramarathon runners. METHODS: 14 runners (11 males, 3 females; 36.9 ± 6.1 yrs, 72.5 ± 11.9 kg) completed the Bear 100 (7200m of vertical gain). Pre-, post-, and 24-h post-race completion, a survey to assess GI symptom presence was completed and weight and a urine sample was collected. Scored on a 10-point scale (0 = no problems; 10 = worst it has ever been), GI symptoms were divided into 1) upper abdominal, 2) lower abdominal, and 3) systemic sections. Urine samples were analyzed for color (U COL ; 1 = good; 8 = severe dehydration) and specific gravity (U SG ). Comparisons for U COL and U SG were made using a paired t-test (p < 0.05). RESULTS: Runners completed the race in 29.85 ± 1.95 h (range: 26.32 – 32.65 h). GI complaints were reported by 85.71% of runners pre- vs. 100% at post- and 24-h post-race. The most frequently reported pre-race GI symptoms (section; %experiencing symptom) included belching (upper; 28.57%), urge to defecate (lower; 50.0%), and urge to urinate (systemic; 64.29%). The most frequently reported post-race GI symptoms included stomach pain/cramps (upper; 100%), flatulence and urge to defecate (lower; 92.86%), and urge to urinate (systemic; 100%). At 24-h post-race the most frequently reported symptoms included reflux/heartburn and belching (upper; 100%), urge to defecate, loose stool, and diarrhea (lower; 100%), and muscle soreness/weakness (systemic; 100%). Post-U SG (1.027 ± 0.010) was significantly higher than pre- (1.015 ± 0.007; t(13) = -6.583, p < 0.001) and 24-h post-U SG (1.017 ± 0.011; t(11) = 2.981, p = 0.013). Similarly, post-U COL (6.5 ± 1.5) was significantly higher than pre-U COL (4.9 ± 1.5; t(13) = -2.785, p = 0.015) and 24-h post-U COL (4.6 ± 2.3; t(11) = 2.723, p = 0.020). CONCLUSION: Runners of the Bear 100 arrived hydrated, ended the race hypohydrated, and began recovering euhydration by 24-h after completing the Bear 100. The high prevalence of GI symptoms suggests runners should continue to prioritize training the GI tract during training (e.g., hydration and fueling strategies) to minimize GI symptomology and fluid losses experienced during the race.