Does exercise affect large gut function?

Abstract

The effect of exercise on large intestinal function has been determined in 14 healthy but normally sedentary men and women, aged 22–34 years while on a constant diet. For an initial 3–5 week period (control) no activity was allowed. Six subjects then undertook a 9 week training schedule by the end of which they were capable of jogging for 1 h/day, 5 days a week. A further six subjects undertook a similar training schedule that lasted for only 7 weeks, at the end of which they were jogging for 45 min/day. Finally, two subjects were studied continuously while taking light exercise for 6 weeks and then jogging for a further 3 weeks. Physical fitness was monitored and showed significant changes with maximum aerobic capacity increasing from 2.4+0.5 to 3.1+0.4 l/min, maximum heart rate after a step test falling from 1524–8 to 129+5 beats/min, and resting pulse rate also falling from 56+4 to 50+5 beats/min. High-density lipoprotein cholesterol also increased significantly. Colonic function was assessed by measurement of stool weight and transit time, using the continuous radio-opaque marker technique, faecal pH, nitrogen excretion, and ammonia concentration. No change was observed overall in mean daily faecal weight (124 + 39 (control) and 129+49 g/day (exercise), transit time (55+20 (control) and 54+23 h (exercise)), nor in faecal frequency, dry stool weight, pH, ammonia, or in total nitrogen excretion. Significant changes did occur in five individuals with significant slowing of transit time in two and speeding up in three. Overall transit time increased in nine subjects and decreased in five. Hence, when diet is constant, exercise has marked effects on physical fitness but no consistent effect on large bowel function.