Impact of Ageing on Female Metabolic Flexibility: A Cross-Sectional Pilot Study in over-60 Active Women

Ageing affects metabolic flexibility, although physical status could influence this relationship. This cross-sectional study aims to describe and analyse the metabolic flexibility/inflexibility in a group of active older women, together with the impact of ageing and physical status on their oxidation rates and maximal fat oxidation (MFO).

Fifteen volunteers (69.00 ± 6.97 years)-from 24 women-completed an incremental cycling test until the second ventilatory threshold. Intensity increased 10 W each 3 min 15 s, starting at 30 W. Gas exchange, heart rate, rate of perceived effort, pain scale and muscle power were registered, together with lactate. VO₂ and VCO₂ were considered for fat and carbohydrate oxidation (FATox and CHOox; Frayn's equation) at intensities 60%, 80% and 100% from the peak power in the test (P₁₀₀). Psychophysiological parameters were compared at MFO/FATmax and P₁₀₀, together with the energy expenditure calculations around MFO (included FAT and CHO contributions), and the main correlation analyses, with and without P₁₀₀ and VO₂ as covariates.

FATox was low at MFO (0.13; 95% CI [0.09-0.17] mg/min/kgFFM; 3.50; 95% CI [2.49-4.50] mg/min/kgFFM), with short oxidation-rate curves shifting down and leftward. CHOox and FATox were both low for reduced power with age (77.14 ± 18.58 W and 39.29 ± 9.17 W at P₁₀₀ and MFO, respectively), all accompanied by a fall in energy expenditure (5.44 ± 2.58 kcal/min and 3.32 ± 1.55 kcal/min at P₁₀₀ and MFO, respectively). Power appears as a determinant factor, given its strong and negative significant association with age (r = - 0.85, p < 0.005; R² = 0.72) and moderate with MFO (r = - 0.54, p = 0.04; R² = 0.29). In turn, energy expenditure shows a positive and moderate association with muscle power (r = 52, p = 0.04).

Despite the drop in substrates oxidation with age, physical status (i.e. larger muscular power and energy expenditure) suggests a key role in the preservation of metabolic health with ageing in active women.