The influence of exercise intensity and exercise mode on gastrointestinal damage

Strenuous exercise increases gastrointestinal damage, but the dose-response relationship is yet to be elucidated. It is also commonly believed that running causes greater gastrointestinal damage than cycling. Two randomised, cross-over studies aimed to 1) quantify gastrointestinal damage with increasing exercise intensity, and 2) determine if running was associated with greater gastrointestinal damage than cycling. Following a V̇O_2max test, participants completed three cycling trials at different intensities (60min at 40%, 60% and 80% V̇O_2max; n=10 (5 female, 5 male)) (INTENSITY), or one running and one cycling trial (45min at 70% V̇O_2max; n=11 (3 female, 8 male)) (MODE). Venous blood samples were collected pre- and post- exercise to measure gastrointestinal damage via intestinal fatty acid binding protein (I-FABP). In INTENSITY, I-FABP magnitude of change was greater at 80% V̇O_2max than 40% V̇O_2max (p<0.01). In MODE, I-FABP magnitude of change was greater with cycling (mean (SD)) (84.7 (133.2)% d=1.07) compared to running (19.3 (33.1)%, d=0.65) with a moderate effect (d=0.68, p=0.024). RPE and HR were higher during cycling (RPE p<0.0001; HR p<0.0001) but rectal temperature was not different between modes (p=0.94). While gastrointestinal damage increases with increasing exercise intensity, running was not associated with greater gastrointestinal damage than cycling. Novelty •A fraction of the anaerobic threshold, rather than a fraction of V̇O_2max, may be more predictive of intensity that results in exercise induced gastrointestinal damage •The mode of exercise may not be as important as intensity for inducing gastrointestinal damage •Improving anaerobic threshold may reduce susceptibility to gastrointestinal damage when exercising at high intensities.