Profiling Substrate Utilization Patterns Using Ventilatory Thresholds as Markers of Exercise Intensity

Background: Profiling substrate utilization patterns at different exercise intensities within the ventilatory threshold (VT) training model is one area of research that may improve nutritional practices, exercise prescription, and body composition management. Purpose: The purpose of this study was to examine substrate utilization patterns below VT₁ and below VT₂ in a rested and fatigued state. Methods: Twenty-one recreationally active participants completed a total of three test sessions consisting of one maximal graded exercise test and two 20-minute submaximal steady-state exercise tests within a fourteen-day period. The maximal graded exercise test was used for determination of VO₂max and VTs. The submaximal steady-state exercise tests were used to determine substrate utilization patterns at intensities below VT₁ and below VT₂. One of the submaximal steady-state exercise tests was completed in a rested state while the other was completed in a fatigued state. For the fatigued test session, participants were verbally instructed to partake in strenuous exercise (lower body resistance training, lactate threshold, VO₂max, or anaerobic workouts) within twenty-four hours of the test. For the rested test session, participants were verbally instructed to refrain from strenuous or unaccustomed exercise for at least 24 hours prior to testing. A two-way repeated measures ANOVA was conducted to explore the effects of exercise duration on lipid or carbohydrate utilization rates between the fatigued and rested trials. Results: There was a significant main effect of exercise duration on carbohydrate utilization rates (F(1.25, 18.72) = 30.97, p = <.001). There was a nonsignificant main effect of exercise duration on lipid utilization rates (F(1.67, 33.20) = 3.04, p = 0.07). There was a nonsignificant main effect of fatigue status on lipid (F(1, 15) = .001, p = .971) and carbohydrate (F(1, 15) = .005, p = .943) utilization rates. Conclusions: Carbohydrate usage increased significantly when comparing exercise below VT₁ to between VT₁ and VT₂. Lipid usage increased gradually over time after steady-state was reached at both intensities.