Relationship between fat oxidation and lactate threshold in athletes and obese

The first aim of this study was to determine the exercise intensity that elicited the highest rate of fat oxidation in sedentary, obese subjects (OB; n=10 men, n=10 women) compared with endurance athletes (AT; n=10 men, n=10 women). The second aim was to investigate the relationship between VO2 at the intensity eliciting the highest rate of fat oxidation and the corresponding VO2 at the lactate threshold. Peak oxygen consumption (VO2peak) was determined in 20 AT and 20 OB using an incremental exercise protocol on a cycle ergometer. Based on their VO2peak values, subjects completed a protocol requiring them to exercise for 20 min at three different workloads (55, 65 and 75 % VO2peak), randomly assigned on two separate occasions. The oxidation rates of fat and carbohydrate were measured by indirect calorimetry. The highest rates of fat oxidation were at 75 % VO2peak (AT), and at 65 % VO2peak (OB). The rate of fat oxidation was significantly higher in AT (18.2 ± 6.1) compared with OB women (10.6 ± 4.5 kJ min-1·kg-1) (p < 0.01). There was no significant difference in the rate of fat oxidation for the men (AT 19.7 ± 8.1 vs. OB 17.6 ± 8.2 kJ min-1·kg-1). AT reached LT at a significantly (p < 0.01) higher exercise intensity expressed in VO2peak than obese subjects (AT women 76.4 ± 0.1, men 77.3 ± 0.1 vs. OB women, 49.7 ± 0.1, men 49.5 ± 0.1 % VO2peak). A significant correlation was found between VO2 at LT and VO