Impact of Acute Exercise Intensity and Pattern on Cytokine Function (AEX)

The immune system helps prevent illness, fights off infections, and repairs damaged tissues following an injury. However, when immune cells remain active for prolonged periods of time - a state known as "chronic inflammation" - they can contribute to the development and progression of chronic diseases like heart disease and diabetes. Exercise can reduce the risk of developing many of these diseases and at least part of the health benefits of exercise are due to the ability of exercise to reduce "chronic inflammation". The inflammation-lowering effects of exercise are typically captured by measuring hormone-like molecules released from immune cells called "cytokines" in the blood. In addition to changes in circulating cytokine levels, exercise may also alter how immune cells respond to these cytokines. How exercise intensity (i.e., how hard you are working during exercise) and pattern (i.e., exercising as a long continuous bout or in short intervals) impact the ability of immune cells to respond to cytokines is not well understood. A better understanding of how exercise intensity and pattern of exercise for reducing chronic inflammation may help determine the best types of exercises for improving health and preventing chronic diseases.

Experimental session involving an acute bout of moderate intensity continuous exercise (MICE; continous cycling expending 350 kcal at 70% of lactate threshold)

Experimental session involving an acute bout of high intensity continuous exercise (HICE; continuous cycling expending 350 kcal at 10% of the difference between lactate threshold and VO2peak)

Experimental session involving an acute bout of high intensity interval exercise (HIIT; cycling intervals expending 350 kcal at 10% of the difference between lactate threshold and VO2peak)

Participants will perform an acute bout of continuous cycling at 70% of the power output at lactate threshold until an energy expenditure of 350 kcal is achieved. Blood samples will be obtained immediately before and immediately, 30, and 90 minutes after exercise.

Participants will perform an acute bout of continuous cycling at 10% of the difference between lactate threshold and VO2peak until an energy expenditure of 350 kcal is achieved. Blood samples will be obtained immediately before and immediately, 30, and 90 minutes after exercise.

Participants will perform an acute bout of interval cycling at at 10% of the difference between lactate threshold and VO2peak until an energy expenditure of 350 kcal is achieved. Blood samples will be obtained immediately before and immediately, 30, and 90 minutes after exercise.

Participants will remain in a rested state (i.e., no exercise) for the entire session. Blood samples will be obtained at the same time-points as the exercise sessions.

Inclusion Criteria: 18-35 years of age Body mass index between 18.5-30 kg/m^2 Free of cardiometabolic and autoimmune/inflammatory disease Exclusion Criteria: Competitive endurance athlete Cigarette smoker Currently taking immunomodulatory/anti-inflammatory medications Currently pregnant