Low-intensity exercise elicits maximal fat oxidation in young healthy men

Maximal Fat Oxidation (MFO) is a marker of skeletal muscle oxidative capacity measured through submaximal exercise testing. However, the intensity at which it occurs remains to be evaluated in nonathletic populations. The study investigated the effect of the lowest and highest range of self-selected comfortable walking paces on whole-body fat oxidation. Fourteen young healthy men (age = 28.5 ± 5.0 years, weight = 76.9 ± 10.9 kg, height = 176.9 ± 5.9 cm, BMI= 24.5 ± 2.8, V̇O2max = 3.8 ± 0.6 ml/min) performed a running incremental test (GXT) prior to partaking in two 30-min self-selected walking pace (low and high) trials. Walking paces, V̇O2, V̇CO2, HR, and RPE, were recorded, and substrate oxidation rates were calculated through stoichiometry equations. The MFO rate determined during the GXT was 473 ± 201 mg/min and occurred at 39.6 ± 11.8 % of V̇O2max. Peak fat oxidation (PFO) rates at the lowest (3.5 ± 0.7 km/h) and highest (5.7 ± 0.8 km/h) walking paces were significantly different (p-value=0.001; 254 ± 11 vs. 436 ± 11 mg/min, respectively). The lowest and highest self-selected walking paces corresponded to 21.2 ± 3.8 and 35.8 ± 5.9 % V̇O2max, respectively. At the highest walking pace, no statistical difference was observed between MFO and PFO