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 HR), oxygen consumption ( O) and heart rate (HR) at ventilatory threshold 1 ( O HR), ventilatory threshold 2 ( O, HR) and at maximal effort ( O, HR) 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) VT and VT. At baseline, age, body composition, O O, and HR were similar in both groups. However, O was higher in OVER (P = 0.033), whereas HR and HR were higher in UNDER (P < 0.05). O (9.0%) and HR (2.2%) improved similarly in both groups. O and O improved with training in both groups (P < 0.001) but the improvement was larger in OVER versus UNDER in O (P = 0.013) and tended to be higher in O (P = 0.068). HR increased only in OVER (P < 0.001), whereas HR did not change in any group (P = 0.248). A 16-week programme of HIIT improves O similarly in individuals training at intensities over or under their VTs. However, individuals training over their VTs showed a larger improvements in O expanding exercise workloads fuelled by oxidative metabolism.