Metabolic Flexibility and Mechanical Efficiency in Women Over-60

Indirect Calorimetry-Based Novel Approach for Evaluating Metabolic Flexibility and Its Association with Circulating Metabolic Markers in Middle-Aged Subjects

We propose a novel method for assessing metabolic flexibility (MF) through indirect calorimetry. A total of twenty healthy volunteers (10 females; 10 males) aged 45-65 were categorized into a Low-Intensity activity group (LI, 0-1 session of 1 h per week) and a High-Intensity activity group (HI, 5-6 sessions of 2 h per week). Volunteers underwent a stepwise exercise test on a cycle ergometer, connected to a calorimeter, to examine respiratory gas exchange to evaluate peak fatty acid Oxidation (PFO) and peak carbohydrate oxidation (PCO). Circulating peroxisome proliferator-activated receptor α (PPARα) biomarkers, docosahexaenoic acid/eicosapentaenoic acid (DHA/EPA) ratio and N-oleoylethanolamine (OEA), and the endocannabinoid- 2-arachidonoylglycerol (2-AG), were evaluated. We developed two MF parameters: the MF index (MFI), calculated by the product of PFO normalized per kg of fat-free mass (FFM) and the percentage of VO2max at PFO, and the peak energy substrates' oxidation (PESO), computed by summing the kilocalories from the PFO and PCO, normalized per kg FFM. The MFI and PESO were significantly different between the HI and LI groups, showing strong correlations with the circulating bioactive substances. Higher DHA/EPA ratio (p ≤ 0.05) and OEA (p ≤ 0.01), but lower 2-AG levels (p ≤ 0.01) were found in the HI group. These new parameters successfully established a functional link between MF and the balance of PPARα/endocannabinoid systems.

Toward Exercise Guidelines for Optimizing Fat Oxidation During Exercise in Obesity: A Systematic Review and Meta-Regression

BACKGROUND

Exercise training performed at maximal fat oxidation (FATmax) is an efficient non-pharmacological approach for the management of obesity and its related cardio-metabolic disorders.

OBJECTIVES

Therefore, this work aimed to provide exercise intensity guidelines and training volume recommendations for maximizing fat oxidation in patients with obesity.

METHODS

A systematic review of original articles published in English, Spanish or French languages was carried out in EBSCOhost, PubMed and Scopus by strictly following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement. Those studies that analyzed maximal fat oxidation (MFO) and FATmax in patients with obesity (body fat > 25% for men; > 35% for women) by calculating substrate oxidation rates through indirect calorimetry during a graded exercise test with short-duration stages (< 10 min) were selected for quantitative analysis. The accuracy of relative oxygen uptake (% peak oxygen uptake [%[Formula: see text]O2peak]) and relative heart rate (% peak heart rate [%HRpeak]) for establishing FATmax reference values was investigated by analyzing their intra-individual and inter-study variation. Moreover, cluster analysis and meta-regression were used for determining the influence of biological factors and methodological procedures on MFO and FATmax.

RESULTS

Sixty-four manuscripts were selected from 146 records; 23 studies only recruited men (n = 465), 14 studies only evaluated women (n = 575), and 27 studies included individuals from both sexes (n = 6434). The majority of the evaluated subjects were middle-aged adults (aged 40-60 y; 84%) with a poor cardiorespiratory fitness (≤ 43 mL·kg-1·min-1; 81%), and the reported MFO ranged from 0.27 to 0.33 g·min-1. The relative heart rate at FATmax (coefficient of variation [CV]: 8.8%) showed a lower intra-individual variation compared with relative oxygen uptake (CV: 17.2%). Furthermore, blood lactate levels at FATmax ranged from 1.3 to 2.7 mmol·L-1 while the speed and power output at FATmax fluctuated from 4 to 5.1 km·h-1 and 42.8-60.2 watts, respectively. Age, body mass index, cardiorespiratory fitness, FATmax, the type of ergometer and the stoichiometric equation used to calculate the MFO independently explained MFO values (R2 = 0.85; p < 0.01). The MFO in adolescents was superior in comparison with MFO observed in young and middle-aged adults. On the other hand, the MFO was higher during treadmill walking in comparison with stationary cycling. Body fat and MFO alone determined 29% of the variation in FATmax (p < 0.01), noting that individuals with body fat > 35% showed a heart rate of 61-66% HRpeak while individuals with < 35% body fat showed a heart rate between 57 and 64% HRpeak. Neither biological sex nor the analytical procedure for computing the fat oxidation kinetics were associated with MFO and FATmax.

CONCLUSION

Relative heart rate rather than relative oxygen uptake should be used for establishing FATmax reference values in patients with obesity. A heart rate of 61-66% HRpeak should be recommended to patients with > 35% body fat while a heart rate of 57-64% HRpeak should be recommended to patients with body fat < 35%. Moreover, training volume must be higher in adults to achieve a similar fat oxidation compared with adolescents whereas exercising on a treadmill requires a lower training volume to achieve significant fat oxidation in comparison with stationary cycling.

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

Background

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).

Methods

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.

Results

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).

Conclusions

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.