Impact of ageing on female metabolic flexibility: a cross-sectional pilot study in over-60 active women

Abstract

Background Ageing influences the metabolic flexibility, albeit the physical status could determine 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). Methods Fifteen volunteers (69.00±6.97 years) from 24 women, completed an incremental cycling test until the second ventilatory threshold. Intensity increased 10W each 3min–15sec, starting at 30W. 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 CHO oxidation (FATox & CHOox; Frayn’s equation) at the intensities 60%, 80% and 100% from the peak of power in the test (P100). Psychophysiological parameters were compared at MFO/FATmax and P100, together with the main correlation analyses, with and without P100 and VO2 as covariates. Results FATox was low at MFO (0.13; 95%CI [0.09-0.17] g·min−1·kg; 5.61 [3.59-7.63] g·min−1·kg FFM), with a shifting down and leftward of a short oxidation-rate curves. CHOox and FATox were both low for a reduced power with age (77.14±18.58 W & 39.29±9.17 W at P100 and MFO respectively), pointing to metabolic inflexibility in older women despite being active. Notwithstanding, the negative correlation between age and MFO (r=-0.54, p=0.04; R2=0.29) disappeared when normalized with P100 (r=-0.17, p=0.53), which was in turn strongly and negatively associated to age (r=-0.85, p<0.005; R2=0.72). P100 was also positive and moderately associated to MFO (r=0.71, p=0.01; R2=0.50). Conclusions Despite the inflexibility with age, physical status (i.e., larger muscular power) suggest a key role in the preservation of the metabolic health with aging in active women.

Metabolic Flexibility and Mechanical Efficiency in Women Over-60

“…Also to account, this correlation between GE and CHOox peak might have been affected by the anticipated RER≈1, consequence of the early predominance of carbohydrates, likely due to mitochondrial dysfunction ( Zia et al, 2022 ), the long stages in the protocol (>3-min), and/or the limited strength in older women ( Monferrer-Marín et al, 2022 ). Indeed, some factors concerning large protocols induce fatigue in less fit, inactive or older population as compared to shorter protocols ( Chura et al, 2012 ).…”

“…The test started at 30 W to allow women complete a minimum overall duration, and the 15-s were added in every stage due to the mechanical limitations of this population ( Yamauchi et al, 2010 ). The increase in intensity was continuously monitored and adjusted with the help of an iPad tablet (Apple, Cupertino, CA, United States) - see Monferrer-Marín et al (2022) for more details-.…”

“…Frayn’s equations were used for the calculation of the whole-body oxidation rates, with the assumption of urinary nitrogen excretion rate as negligible ( Frayn, 1983 ), at the intensities 60, 80 and 100% of the individual peak of power in the test (P 60 , P 80 and P 100 respectively) ( Monferrer-Marín et al, 2022 ). …”

“…Importantly, these conditions causing impaired metabolic flexibility yield to a mitochondrial evolution towards a more glycolytic phenotype ( Hyatt and Powers, 2021 ). Nevertheless, this evolution shows a smaller increase in the older adults despite their impoverished lipid metabolism ( Braganza et al, 2019 ; Monferrer-Marín et al, 2022 ), what becomes a limiting factor for physical exercise.…”

“…In this context, Monferrer-Marín et al (2022) have introduced muscle power as a control variable in their recent pilot study about the association of metabolic flexibility and aging in older women, downplaying the link between age and metabolic inflexibility. According to these authors, both carbohydrates and fat oxidation rates (CHOox and FATox respectively) confirm to be lower in this population.…”