OBJECTIVES: This study examined the effects of 6 weeks of high-intensity training (HIT) on lipid oxidation (LO) rates during incremental exercises in obese adults. METHODS: Twenty-four obese adults were randomised into a no-exercise control group (n = 12; body mass index 33.3 (4.8) kg/m2) and a HIT group (18 sessions of 6x6 s of supramaximal cycling and 2 min passive intervals; n = 12; body mass index 33.2 (2.8) kg/m2). The percentage of LO contribution was computed at rest and for all workloads (25, 50, 75, 100 and 125 W) in both groups before and after training via a graded maximal cycling test. RESULTS: After training, the HIT group showed significantly higher LO at rest and at 25, 50 and 75 W compared with baseline (p < 0.01) and the control group (p < 0.01). Moreover, for the training group, the homoeostasis model assessment of insulin resistance (HOMA-IR) index decreased significantly from the baseline value (p < 0.01) and the control group value (p < 0.01). The increases in LO observed at rest and stages 25, 50 and 75 W were positively correlated with the declines in the HOMA-IR index (r = 0.87, r = 0.83, r = 0.91 and r = 0.88; p < 0.01). CONCLUSION: In obese adults, HIT increased lipid contributions to energy release at rest and in response to incremental exercise, while there were no changes in participants' aerobic capacity. This supports the hypothesis that metabolic changes rather than improved aerobic capacity are important to improve LO. TRIAL REGISTRATION NUMBER: ISRCTN66508384. Stage: post-results.

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