Exercise Performed In Hypobaric Hypoxia Increases Markers Of Intestinal Injury And Symptoms Of Gastrointestinal Distress

Abstract

Gastrointestinal (GI) complications (nausea, diarrhea, weight loss, intestinal bleeding) have been reported during high altitude ascent and their underlying cause might be related to intestinal injury. Exercise at high altitude exacerbates GI symptoms, but it is not known if markers of intestinal injury increase or are associated with GI symptoms during exercise. PURPOSE: To determine the effect of exercise in hypobaric hypoxia on markers of intestinal injury, bacterial translocation, and GI symptoms. METHODS: Using a randomized and counterbalanced design 9 males completed two experimental trials: one at simulated 4300 m of hypobaric hypoxia (HYP) and one at local altitude of 1585 m (NORM). For both trials participants performed 60-minutes of cycling at a workload that elicited 65% of their NORM VO2max. GI symptoms were assessed before and every 15-minutes during exercise. Pre- and post-exercise blood samples were assessed for markers of intestinal injury (I-FABP & CLDN-3) and bacterial translocation (LBP) using ELISA kits. Data were analyzed using two way (time x condition) repeated measures ANOVAs. Effect sizes are provided as Cohen’s d (d). Correlations were used to determine relationships between GI symptoms and pre-to post-exercise change (Δ) in I-FABP, CLDN-3, and LBP. RESULTS: All 9 participants reported at least one GI symptom in HYP compared to just 1 participant in NORM. I-FABP was significantly elevated from pre- to post-exercise in HYP (708 ± 191 to 1215 ± 518 pg/mL; p ≤ 0.05 d = 1.10) but not in NORM (759 ± 224 to 828 ± 288 pg/mL; p > 0.05 d = 0.27). CLDN-3 was significantly elevated from pre- to post-exercise in HYP (13.8 ± 0.9 to 15.3 ± 1.2 ng/mL; p ≤ 0.05 d = 1.19) but not in NORM (13.7 ± 1.8 to 14.2 ± 1.6 ng/mL; p > 0.05 d = 0.45). LBP was significantly elevated from pre- to post-exercise in HYP (10.8 ± 1.2 to 13.9 ± 2.8 μg/mL; p ≤ 0.05 d = 1.12) but not in NORM (11.3 ± 1.1 to 11.7 ± 0.9 μg/mL; p > 0.05 d = 0.32). I-FABP (d = 0.85), CLDN-3 (d = 0.95), and LBP (d = 0.69) were all significantly higher post-exercise in HYP compared to NORM (p ≤ 0.05). Overall GI discomfort was significantly correlated to ΔI-FABP (p ≤ 0.05 r = 0.50) and ΔLBP (p ≤ 0.05 r = 0.85), but not CLDN-3 (p > 0.05 r = 0.33). CONCLUSIONS: These data indicate that cycling exercise performed in HYP can damage the intestinal barrier which might explain some of the commonly reported GI symptoms.