Baseline Ventilatory Thresholds Determine Cardiorespiratory Adaptations to High-Intensity Interval Training in Obese Participants

Abstract

PURPOSE: To study if cardiorespiratory fitness (CRF) evolution after high intensity interval training (HIIT) depends on training intensity relative to ventilatory thresholds (VTs). METHODS: A sample (n=134) of sedentary participants with obesity (54±9 years, BMI 31.6±5.6 kg·m-2, 42% female) trained for 16 weeks, 3 days·week-1 alternating bouts of 70-90% of peak heart rate (HR). CRF was evaluated before and after training using a graded cycle-ergometer exercise tests (GXT) until exhaustion. Starting at rest, oxygen consumption (VO2), power output (PO), and HR, were determined at ventilatory threshold (VT1), respiratory compensation threshold (VT2) and at maximal values (PEAK). Participants were separated in two groups according to the relationship between the training intensity (target-HR based) and the VTs location. One group (BelowVTs) was composed for those who trained below their VTs (n=74), whereas the other group (AboveVTs) for those who trained above their VTs (n=60). RESULTS: Before intervention, age and body composition were similar in both groups. While at baseline, VO2 at PEAK was higher in AboveVTs (P=0.005), at VT1, and VT2, was similar in both groups. After training, both groups improved their VO2PEAK by 11-12% (P<0.001) without differences between groups (P=0.880). However, in BelowVTs group, 54% of the VO2, improvement occurred below VT1, 12% between VTs and 33% above VT2, whereas for AboveVTs, 96% of the VO2 improvement occurred below VT1, 0% between VTs and 4% above VT2. CONCLUSIONS: Target-HR based HIIT improves VO2PEAK in middle-aged individuals with obesity independently of the VTs location. However, the extent of the widening of exercise workloads tolerated after the onset of metabolic acidosis (i.e., improvements above VT2) and exercise workloads supplied solely with oxidative metabolism (i.e., improvements at VT1) depends if the workload chosen for training fall above or below the workload at both VTs.