Determination and validation of peak fat oxidation in endurance-trained men using an upper body graded exercise test

Peak fat oxidation rate (PFO) and the intensity that elicits PFO (Fat_max) are commonly determined by a validated graded exercise test (GE) on a cycling ergometer with indirect calorimetry. However, for upper body exercise fat oxidation rates are not well elucidated and no protocol has been validated. Thus, our aim was to test validity and inter-method reliability for determination of PFO and Fat_max in trained men using a GE protocol applying double poling on a ski-ergometer. PFO and Fat_max were assessed during two identical GE tests (GE1 and GE2) and validated against separated short continuous exercise bouts (SCE) at 35%, 50%, and 65% of V̇O_2peak on the ski-ergometer in 10 endurance-trained men (V̇O_2peak: 65.1 ± 1.0 mL·min⁻¹·kg⁻¹, mean ± SEM). Between GE tests no differences were found in PFO (GE1: 0.42 ± 0.03; GE2: 0.45 ± 0.03 g·min⁻¹, P =.256) or Fat_max (GE1: 41 ± 2%; GE2: 43 ± 3% of V̇O_2peak, P =.457) and the intra-individual coefficient of variation (CV) was 8 ± 2% and 11 ± 2% for PFO and Fat_max, respectively. Between GE and SCE tests, PFO (GE_avg: 0.44 ± 0.03; SCE; 0.47 ± 0.06 g·min⁻¹, P =.510) was not different, whereas a difference in Fat_max (GE_avg: 42 ± 2%; SCE: 52 ± 4% of V̇O_2peak, P =.030) was observed with a CV of 17 ± 4% and 15 ± 4% for PFO and Fat_max, respectively. In conclusion, GE has a high day-to-day reliability in determination of PFO and Fat_max in trained men, whereas it is unclear if PFO and Fat_max determined by GE reflect continuous exercise in general.