Cade Carter, Jakob D. Lauver, Timothy R. Rotarius. Coastal Carolina University, Conway, SC.

Background: The VO2 slow component (VOSC) is a slow, exponential increase in VO2 that takes place during constant load exercise above the ventilatory threshold (VT). Purpose: This study aimed to examine the amplitude of the VO2SC during various heavy intensity interval exercise protocols when controlling the VO2 on-kinetics. Methods: Six males (24 ± 5 yrs.) participated in a total of 7 visits. The first visit consisted of a graded exercise test (20 W/min) until volitional fatigue. VO2peak was determined as the highest VO2 averaged over a 15-second interval, and was used to determine the subject’s work rates for each experimental condition that corresponded with 50% of the difference between VO2peak and VT (Δ50%). The three experimental conditions were: continuous (CON), intermittent (INT), and extended intermittent (EXT), two trials were completed for each condition. Pulmonary gas exchange (VO2, VCO2) and minute ventilation (VE) were measured through breath-by-breath analysis. Each experimental condition consisted of a 4-minute warm-up (20W), followed by heavy intensity exercise. To control on-transition kinetics, the work rate during the initial 3 min for each condition was kept the same. During CON, work rate was unchanged for 3 additional min. During INT, the remaining 3 min consisted of 3 s rest intervals interspersed every 10 s. For the EXT condition, 3 s recovery intervals were inserted every 10 s until the total work performed matched the total work performed for the CON condition. Phase II VO2 responses (time constant, τVO2) were analyzed using either a 2- or 3-component exponential model after interpolating to 1 s and ensemble averaging each trial. One-way ANOVAs were computed to assess the difference in means for each condition. Significance was established if p < 0.05. Results: τVO2 was similar (CON: 32.5 ± 1.7 s; INT: 36.6 ± 1.8 s; EXT: 36.1 ± 2.6 s, p=0.50) as expected. The amplitude of VO2SC, as measured by ΔVO2(6-3), was decreased in both INT and EXT compared to the CON condition (-8 ± 35 mL/min; -39 ± 43 mL/min; 367 ± 50 mL/min, p < 0.001). ΔHR(6-3) was lower in INT and EXT (3 ± 2 bpm; 3 ± 1 bpm, respectively) compared to CON (15 ± 2 bpm, p < 0.001). Conclusion: These findings suggest that the VO2SC was abolished with the addition of 3 s recovery intervals (INT and EXT). This is possibly due to myocardial work, as evidence by ΔHR(6-3), being lower in INT and EXT compared to CON.

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