Metabolic Differences During Submaximal, Steady-State Aerobic Exercise between Sarcopenic and Non-Sarcopenic Older Adults

Abstract

Abstract Objectives To examine differences in metabolic flexibility during submaximal aerobic exercise in sarcopenic (S) and non-sarcopenic (NS) older adults. Methods Twenty-two older adults (mean age ± SE = 77 ± 2) were categorized as NS (n = 11) and S (n = 11) based on grip strength and muscle mass. Participants completed an aerobic, steady-state 10-min walk on a treadmill at 50 – 60% of their estimated V̇O2 max. Indirect calorimetry was assessed at baseline (fasted) and during the treadmill test to analyze respiratory quotient (RQ), carbohydrate (CHO) oxidation and fat oxidation, and % contributions of CHO and fat oxidation to energy expenditure (%CHO and %FAT, respectively). Two-way mixed factorial ANOVAS (time x group) and follow up t-tests were used to examine between group differences. Results At baseline, RQ was higher (0.76 ± 0.01 vs. 0.72 ± 0.01, p = 0.025) and fat oxidation was lower (0.08 ± 0.01 vs. 0.11 ± 0.01 g · min−1, p = 0.003) in S than NS individuals. The S group had significantly greater %CHO versus %FAT from 6 – 10 min of exercise (p = 0.005–0.014), whereas NS individuals maintained an approximately equal distribution of %CHO and %FAT until 8 – 10 min (p = 0.034–0.047). RQ (0.90 ± 0.06 vs. 0.86 ± 0.01, p = 0.039) and %CHO (70% vs. 57%, p = 0.046) were greater in S compared to NS at 8 min of exercise. Fat oxidation was consistently higher in NS than S individuals from 4 - 10 of min exercise (p = 0.016–0.045). Conclusions Since skeletal muscle utilizes a large amount of energy during exercise, metabolic flexibility is key to efficiently utilize both CHO and fat sources to generate energy to match metabolic demands. Our data reveals that NS individuals were able to rely on both fuel sources during submaximal exercise indicating metabolic flexibility. Typically, exercising at 50 – 60% V̇O2 max utilizes 50% CHO and 50% fat contributions to energy expenditure, as observed in NS individuals. On the other hand, in S individuals, CHO composed a much larger proportion of total energy usage during exercise. These findings suggest that S individuals have low metabolic flexibility with higher dependence on CHO for energy during low-moderate aerobic activity. Funding Sources This study was funded by Abbott Nutrition.