Influence of intensity fluctuation on exercise metabolism

This investigation was undertaken to examine the influence of intensity fluctuation on metabolic responses during and after exercise. Twenty-four males and 24 females were randomly assigned into one of the four groups consisting of 12 subjects of equal gender. Each group performed one of four 30-min exercise protocols: (1) cycling at a constant power output of 75 W (P1), (2) cycling with power output alternating between 50 and 100 W every 5 min (P2), (3) same as P2 except power output was alternated in a reverse order (P3), and (4) same as P2 except power output was alternated between 25 and 125 W (P4). Each exercise session was followed by a 25-min recovery and all protocols yielded the same mechanical work. Oxygen uptake (VO₂), heart rate (HR), respiratory exchange ratio (RER), and plasma lactate concentrations ([La]) were measured at rest and during exercise and recovery. Ratings of perceived exertion (RPE) were recorded during exercise only. During exercise, VO₂, HR and RPE did not differ across the four protocols. RER was higher (P < 0.05) in P4 than P1 and P2. [La] was higher (P < 0.05) in P4 than P1 and P3. During recovery, VO₂ were lower (P < 0.05) in P1 than P2, P3, and P4, while [La] was higher in P4 than P3. When the total workload was equated, intensity fluctuation exerted no added effect upon metabolic responses during exercise, but provoked greater energy expenditure following exercise. Reversing the order or increasing the magnitude of intensity fluctuation would not further alter metabolic consequences.