Impact of exercise duration on gastrointestinal function and symptoms

The study aimed to determine the impact of exercise duration on gastrointestinal functional responses and gastrointestinal symptoms (GIS) in response to differing exercise durations. Endurance runners (n=16) completed three trials on separate occasions, randomised to 1 h (1-H), 2 h (2-H) and 3 h (3-H) of running at 60% V̇O2max in temperate ambient temperature. Orocecal transit time (OCTT) was determined by lactulose challenge, with concomitant breath hydrogen (H2) determination. Gastric slow wave activity was recorded using cutaneous electrogastrography (cEGG) pre and post exertion. GIS was determined using a modified visual analogue scale (mVAS). OCTT response was classified as very slow on all trials (~93-101 min) with no trial difference observed (P= 0.895). Bradygastria increased post-exercise on all trials (mean ± SD: 1-H: 10.9 ± 11.7%, 2-H: 6.2 ± 9.8% and 3-H: 13.2 ± 21.4%; P< 0.05). A reduction in the normal gastric slow wave activity (2-4 cycles/min) was observed post-exercise on 1-H only (-10.8 ± 17.6%; P= 0.039). GIS incidence and gut discomfort was higher on 2-H (81% and 12 counts) and 3-H (81% and 18 counts), compared to 1-H (69% and 6 counts) (P= 0.038 and P= 0.006, respectively). Severity of gut discomfort, total-GIS, upper-GIS, and lower-GIS increased during exercise on all trials (P< 0.05). Steady state exercise in temperate ambient conditions for 1 h, 2 h, and 3 h instigates perturbations in gastric slow wave activity compared to rest and hampers OCTT, potentially explaining the incidence and severity on exercise-associated GIS.