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.

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.

Metabolic flexibility can be defined as the ability of the skeletal muscle to adjust its utilization of substrate pathways

Objective: The purpose of this study was to determine the prevalence of poor iron status in young athletes throughout the stages of iron deficiency and assess sex differences with iron deficiency in relation to growth and development and dietary intake. Methods: A cross-sectional analysis evaluated young male and female athletes (n = 91) between the ages 8 and 16 years. Anthropometric assessments, body composition, dietary intakes, and blood samples measuring ferritin, soluble transferrin receptor (sTfR), and hemoglobin (Hb) were examined. Prevalence was calculated as percentages, and independent samples t tests examined sex differences. Pearson product-moment correlation coefficient analyses quantified relationships among variables for the composite sample and each sex separately. Results: Iron depletion (low ferritin) was present in 65% and 86%, low iron levels (sTfR) in 51% and 68%, and anemia (low Hb) in 46% and 53% of the males and females, respectively. As iron deficiency progressed from low ferritin to high sTfR to anemia, prevalence decreased in both sexes, but always remained higher in females. Males were greater than females for weight, arm muscle size, and ferritin concentrations, while females were greater than males for biological maturity (p ≤ 0.05). Dietary iron intake was moderately to highly correlated (r = 0.543–0.723, p ≤ 0.05) with growth and development in females, but not males. Conclusions: Prevalence of poor iron status was higher than expected, particularly in adolescent females. Since rapid growth combined with sports participation may create high demands for iron bioavailability, emphasis may need to be placed on dietary iron intake for young athletes, particularly females.

There is conflicting evidence of the roles vitamin D and iron have in isolation and combined in relation to muscle health. The purpose of this narrative review was to examine the current literature on the roles that vitamin D and iron have on skeletal muscle mass, strength, and function and how these nutrients are associated with skeletal muscle health in specific populations. Secondary purposes include exploring if low vitamin D and iron status are interrelated with skeletal muscle health and chronic inflammation and reviewing the influence of animal-source foods rich in these nutrients on health and performance. PubMed, Scopus, SPORT Discus, EMBAE, MEDLINE, and Google Scholar databases were searched to determine eligible studies. There was a positive effect of vitamin D on muscle mass, particularly in older adults. There was a positive effect of iron on aerobic and anaerobic performance. Studies reported mixed results for both vitamin D and iron on muscle strength and function. While vitamin D and iron deficiency commonly occur in combination, few studies examined effects on skeletal muscle health and inflammation. Isolated nutrients such as iron and vitamin D may have positive outcomes; however, nutrients within food sources may be most effective in improving skeletal muscle health.

Bone loss throughout life is a normal consequence of aging; however, some people are more predisposed to developing osteoporosis and sustaining associated fractures than others. But the risk of osteoporosis can be reduced by: (1) maximizing skeletal mass during the growing years, (2) consuming 1,000 to 1,500 mg of calcium per day, (3) participating in lifelong weight-bearing exercise, and (4) considering pharmacologic intervention at menopause. Pharmacologic options include calcium, vitamin D, estrogen, bisphosphonates, selective estrogen receptor modulators, and calcitonin. Any such medication should be taken in conjunction with exercise and fall precautions.