One of the most important benefits of exercise is in how it reduces our risk of developing a number of types of cancer — especially colorectal cancer, which according to some estimates is the malignancy most influenced by physical activity. But how workouts guard against colon cancer remains largely unknown. Physical activity speeds the movement of waste through the intestines, as anyone who has had to hunt for a bathroom during a workout knows. But this does not seem to fully account for the protective effects of exercise. Instead, a small study published in February in The Journal of Physiology suggests we should also look to changes in our bloodstream after exercise.

The new study began with scientists at the University of Queensland in Brisbane, Australia, and other institutions recruiting 20 men who had survived colon cancer. (Women were excluded because menstruation might have affected results.)

The scientists asked 10 of the men to start working out strenuously three times a week: pedaling a stationary bicycle hard for four minutes, resting for three, and repeating that sequence three more times. They trained for a month and then, a few days after completing the program, rested quietly while researchers drew blood. The other 10 men completed the same 4 x 4 interval session, but only once. The researchers drew their blood before, immediately following and an additional two hours after that lone workout.