We investigated the effect of physical exercise on colonic motor activity in the fasted and fed states in six conscious dogs. Each dog was implanted with nine strain gauge transducers: three on the proximal, three on the middle, and three on the distal colon. The dogs ran for 1 h on a treadmill at 5 km/h (slope 5%). In the fasted state, the dogs exercised during the 5th h of recording after an overnight fast, and in the fed state during the 1st, 3rd, and 5th postprandial hour. In the fasted state, exercise significantly decreased the frequency of colonic migrating motor complexes (MMCs) but had no effect on the total or the mean duration of contractile states in the proximal, middle, and distal colon. Postprandially, exercise disrupted colonic MMCs and replaced them with nonmigrating motor complexes in all three periods of exercise (1st, 3rd, and 6th h). Exercise also increased the total duration per hour of contractile activity throughout the colon during the 1st and 3rd h and only in the distal colon during the 6th h after the meal. The dogs never defecated during rest in the fasted or the fed state. Shortly after the start of exercise in the fasted and fed states, giant migrating contractions (GMCs) occurred, and they were followed by defecation. In approximately 40% of the experiments, another GMC originated in the proximal colon, approximately 10 min after the first defecation, and migrated caudad up to the middle colon. These GMCs were not associated with defecation but caused mass movements.(ABSTRACT TRUNCATED AT 250 WORDS)