Maximal fat oxidation assessment in active postmenopausal females: A novel relative power FATmax test

This study compared a novel relative-to-body-mass FATmax test (RFT; 0.15 W/kg/4 min from 0.45 W/kg) with a traditional absolute power FATmax test (AFT; 10 W/3min15sec from 30 W) in postmenopausal females. The aim was to determine whether the RFT protocol would improve fat oxidation kinetics during exercise, in females with lower maximal fat oxidation (MFO). It was hypothesized that the longer duration and the lower workload increments would result in higher fat oxidation values than AFT. Seventeen active postmenopausal females (69.2 ± 5.1 years) performed both protocols in a randomized order and were divided into above (H-MFO) or below (L-MFO) 0.3 g/min MFO. Groups were equal in age and body composition. Overall, time to MFO was delayed during the RFT protocol (765 ± 621 vs. 401 ± 262 s) without MFO differences. Both groups displayed longer time to MFO in RFT, whilst significantly only for L-MFO (420 ± 280 s vs. 317 ± 232). Although no statistical differences, moderate effect sizes were observed in the L-MFO group during RFT for both MFO (0.22 ± 0.04 vs. 0.19 ± 0.06 g/min, d = 0.65) and VO₂ (12.8 ± 3.8 vs. 15.4 ± 5.5 mL/min/kg, d = -0.53). RFT may improve the determination of substrate oxidation kinetics in postmenopausal females with reduced fat oxidation capacity, while facilitating complementary analyses requiring longer recordings and stability (efficiency and Heart Rate Variability).