Training intensity relative to ventilatory thresholds determines cardiorespiratory fitness improvements in sedentary adults with obesity

The aim of the present study was to study if training intensity relative to ventilatory thresholds (VTs) determines the improvements in cardiorespiratory fitness (CRF) in middle-aged sedentary individuals with obesity. Before and after 16-weeks of HIIT (43-min alternating bouts at 70/90% of HRMAX), oxygen consumption (O-2) and heart rate (HR) at ventilatory threshold 1 (O-2VT1,O- HRVT1), ventilatory threshold 2 (O-2VT2, HRVT2) and at maximal effort (O-2MAX, HRMAX) were assessed during a graded cycle-ergometer exercise test. Retrospectively, participants were divided into two groups based on whether training intensities were under (UNDER; n = 39) or over (OVER; n = 37) VT1 and VT2. At baseline, age, body composition, O-2VT1,O- O-2VT2, and HRMAX were similar in both groups. However, O-2MAX was higher in OVER (P = 0.033), whereas HRVT1 and HRVT2 were higher in UNDER (P < 0.05). O-2MAX (9.0%) and HRMAX (2.2%) improved similarly in both groups. O-2VT1 and O-2VT2 improved with training in both groups (P < 0.001) but the improvement was larger in OVER versus UNDER in O-2VT1 (P = 0.013) and tended to be higher in O-2VT2 (P = 0.068). HRVT1 increased only in OVER (P < 0.001), whereas HRVT2 did not change in any group (P = 0.248). A 16-week programme of HIIT improves O-2MAX similarly in individuals training at intensities over or under their VTs. However, individuals training over their VTs showed a larger improvements in O-2VT1 expanding exercise workloads fuelled by oxidative metabolism.