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Background: Metabolic flexibility is the ability of skeletal muscle to adapt fuel utilization to the demand for fuel sources [carbohydrates (CHO) and fats (FAT)]. The purpose of this study was to explore muscle energy metabolism and metabolic flexibility under various conditions in sarcopenic (S) versus nonsarcopenic (NS) older adults., Methods: Twenty-two older adults aged 65 years or older were categorized as NS [n = 11; mean ± standard deviation (SD); age = 73.5 ± 6.0 years (males, n = 5; females, n = 6)] or S [n = 11; 81.2 ± 10.5 years (males, n = 6; females, n = 5) based on handgrip strength, body composition and physical performance. Indirect calorimetry was recorded before and after consumption of a high-CHO meal and during aerobic and anaerobic exercise. Respiratory quotient (RQ), CHO and FAT oxidation were assessed. Venous blood samples were collected for glucose and insulin concentrations., Results: At rest, compared with NS, S exhibited a 5-8% higher RQ at 0 (0.72 vs. 0.76) and 120 (0.77 vs. 0.82), 150 (0.76 vs. 0.80), and 180 min (0.74 vs. 0.80) (P = 0.002-0.025); 59-195% higher CHO oxidation at 0, 120, and 180 min (0.0004-0.002 vs. 0.001-0.002 g·min -1 ·kg -1) (P = 0.010-0.047); and 20-31% lower FAT oxidation at 0, 15, and 90-180 min (0.0009-0.0022 vs. 0.0011-0.002 g·min -1 ·kg -1 ) (P = 0.004-0.038). Glucose levels were significantly elevated in S versus NS at 0, 60 and 75 min (144.64-202.78 vs. 107.70-134.20 mg·dL -1 ) but not insulin. During aerobic exercise, RQ was 5% greater (0.90 vs. 0.86) (P = 0.039), and FAT oxidation was 35% lower at 6-8 min (0.003 vs. 0.005 g·min -1 ·kg -1 ) (P = 0.033) in S versus NS. During anaerobic exercise, CHO oxidation was 31% greater in NS versus S at 60-80% time to exhaustion (0.011 vs. 0.007 g·min -1 ·kg -1 ) (P = 0.015). Per cent contribution to energy expenditure was greater in S for CHO but lower for FAT at 0 (CHO: 22% vs. 10%; FAT: 78% vs. 91%) and 120-180 min (CHO: 35-42% vs. 17-25%; FAT: 58-65% vs. 75%-84%) (P = 0.003-0.046) at rest and 6-8 min during aerobic exercise (CHO: 70% vs. 57%; FAT: 30% vs. 45%) (P = 0.046)., Conclusions: The data show differences in skeletal muscle energy metabolism and substrate utilization between S and NS at rest, transitioning from fasted to fed state, and during exercise. Compared with NS, S displayed a diminished ability to adapt fuel utilization in response to feeding and exercise, reflecting metabolic inflexibility. Impaired metabolic flexibility could be a mechanism underlying the losses of strength and physical function accompanying sarcopenia., (© 2022 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by John Wiley & Sons Ltd on behalf of Society on Sarcopenia, Cachexia and Wasting Disorders.)

Malnutrition and sarcopenia commonly overlap and contribute to adverse health outcomes. Previously, chronic supplementation with two oral nutritional supplements (ONS), control (C ONS ) and experimental ONS enriched with protein, vitamin D and β-hydroxy β-methylbutyrate (HMB) (E ONS ), improved muscle strength and quality in malnourished sarcopenic older adults, with E ONS demonstrating early strength benefits at 12 weeks. To understand the underlying biological mechanisms contributing to the observed early strength benefits of E ONS , we examined serum biomarker changes in response to 12-week supplementation. Serum samples (E ONS ( n = 90) and C ONS ( n = 103)) collected at baseline and 12 weeks were analyzed. Biomarkers ( n = 243) were measured using multiplexed immunoassay, commercial immunoassays and ELISAs. Sixty markers were excluded with levels below assay detection limits. Sixteen biomarkers significantly changed in response to both interventions including nutritional and metabolic markers. Thirteen biomarkers significantly changed in response to E ONS but not C ONS . Increases in immunoglobulins, myoglobin, total protein, vitamin E and magnesium were observed with E ONS . Inflammation-related ferritin and osteopontin decreased, while soluble receptors for cytokines increased, suggesting decreased inflammation. Sex hormone-binding globulin associated with sarcopenia also decreased with E ONS. Biomarkers reflective of multiple biological systems were impacted by nutritional intervention in sarcopenic older adults. Incremental biomarker changes were observed in response to E ONS containing HMB that possibly link to improvements in skeletal muscle health.

This study quantified systematic and intraindividual variability among three repetitions of concentric isokinetic knee extension and flexion tests to determine velocity-related differences in peak torque (PT) and mean power (MP) in healthy elderly (HE) versus sarcopenic and malnourished elderly (SME). In total, 107 HE ( n = 54 men, n = 53 women) and 261 SME ( n = 101 men, n = 160 women) performed three maximal concentric isokinetic knee extension and flexion repetitions at 60°·s -1 and 180°·s -1 . PT for Repetition 3 was lower than Repetitions 1 and 2, while MP for Repetition 1 was lower than Repetitions 2 and 3 in SME. Intraindividual variability among repetitions was correlated with strength, but not age, and was greater in SME, during knee flexion, and at 180°·s -1 . Velocity-related decreases in PT from 60°·s -1 to 180°·s -1 were more pronounced in SME. In summary, (a) the repetition with the highest PT value may be the best indicator of maximal strength, while the average may indicate strength maintenance in SME; (b) intraindividual variability among repetitions reflects functional decrements from HE to SME; and, ((c) decreases in PT from 60°·s to 180°·s may reflect greater losses of fast-twitch (type II) fiber function.)

Background: Recent evidence suggests that nutritional interventions may improve muscle outcomes in malnutrition and sarcopenia., Objectives: We evaluated the effects of 2 high-quality oral nutritional supplements (ONS) differing in amount and type of key nutrients in older adult men and women., Design: A multicenter, randomized, double-blinded, controlled clinical trial., Participants: Malnourished and sarcopenic men and women, 65 years and older (n = 330)., Intervention: A 24-week intervention period with 2 energy-rich (330 kcal) ONS treatment groups: Control ONS (C ONS , 14 g protein; 147 IU vitamin D 3 ) versus Experimental ONS (E ONS , 20 g protein; 499 IU vitamin D 3 ; 1.5 g CaHMB) taken twice daily. Both ONS also contained other vitamins, minerals, and nutrients in varying amounts., Measurements: Isokinetic peak torque (PT, Nm) leg strength, grip strength (kg), and gait speed (m·s -1 ) were assessed at baseline and 12 and 24 weeks. Left and right leg muscle mass (LMM, kg) were assessed by dual-energy x-ray absorptiometry (DXA). Muscle quality (MQ) was leg strength expressed relative to the tested LMM (Nm·kg -1 ). Subgroup analyses were performed: severe sarcopenia (low skeletal mass index, low grip strength [<30 kg men; <20 kg women], low gait speed [<0.8 m·s -1 ]) and mild-moderate sarcopenia (low skeletal mass index, normal gait speed, or normal grip strength)., Results: Both ONS groups (E ONS and C ONS ) improved PT, MQ, grip strength, and gait speed from baseline with no treatment differences. Those with severe sarcopenia (44%) exhibited lower baseline PT and MQ, with no differences in strength improvements between treatments. However, participants with mild-moderate sarcopenia exhibited higher baseline PT and MQ, with differences in strength improvements at 12 weeks (E ONS  > C ONS , P = .032) in those with normal grip strength. There were no treatment differences based on sarcopenic severity for either grip strength or gait speed., Conclusion: ONS improved strength outcomes in malnourished older adults with sarcopenia. In those with mild-moderate sarcopenia, but not severe sarcopenia, consumption of the E ONS improved leg muscle strength and quality compared with the standard C ONS ., (Copyright © 2016 AMDA – The Society for Post-Acute and Long-Term Care Medicine. Published by Elsevier Inc. All rights reserved.)