Preserved skeletal muscle oxidative capacity in older adults despite decreased cardiorespiratory fitness with ageing

Impact of physical activity on physical function, mitochondrial energetics, ROS production, and Ca2+ handling across the adult lifespan in men

Aging-related muscle atrophy and weakness contribute to loss of mobility, falls, and disability. Mitochondrial dysfunction is widely considered a key contributing mechanism to muscle aging. However, mounting evidence positions physical activity as a confounding factor, making unclear whether muscle mitochondria accumulate bona fide defects with aging. To disentangle aging from physical activity-related mitochondrial adaptations, we functionally profiled skeletal muscle mitochondria in 51 inactive and 88 active men aged 20-93. Physical activity status confers partial protection against age-related decline in physical performance. Mitochondrial respiration remains unaltered in active participants, indicating that aging per se does not alter mitochondrial respiratory capacity. Mitochondrial reactive oxygen species (ROS) production is unaffected by aging and higher in active participants. In contrast, mitochondrial calcium retention capacity decreases with aging regardless of physical activity and correlates with muscle mass, performance, and the stress-responsive metabokine/mitokine growth differentiation factor 15 (GDF15). Targeting mitochondrial calcium handling may hold promise for treating aging-related muscle impairments.

SEVERITY OF LUNG OBSTRUCTION AND OLDER AGE, BUT NOT PHYSICAL ACTIVITY, PREDICT LOCOMOTOR MUSCLE OXIDATIVE IMPAIRMENT IN COPD

Background

Low muscle oxidative capacity is an extrapulmonary manifestation of chronic obstructive pulmonary disease (COPD) with unclear etiology. We sought to determine clinical and behavioral features associated with muscle oxidative capacity in smokers with and without COPD and never smoker individuals.

Methods

243 adults enrolled in the Muscle Health Study, an observational study ancillary to COPDGene. Gastrocnemius oxidative capacity was measured by near-infrared spectroscopy from muscle oxygen uptake recovery rate constant (k). Physical activity by accelerometry (vector magnitude units, VMU/min). Pulmonary assessments included spirometry (FEV1%predicted), diffusing capacity (DLCO), and quantitative chest computed tomography (CT). Eighty-seven variables related to COPD features were considered. Variables selected by univariate analysis of log-transformed k with p≤0.20, and filtered by machine learning, were entered into multivariable linear regression to determine association with k.

Results

241(99%) participants were allocated to analysis. FEV1%predicted, DLCO, CT, pack-years, age and VMU/min were among 24 variables selected by univariate analysis. After machine learning filtering on 161(66%) cases with complete data, 11 variables were included in multivariable analysis. Only FEV1%predicted, age and race were significantly associated with k (R2=0.26). Model coefficients equate a 10% lower FEV1%predicted to a 4.4% lower k, or 10-years of aging to a 9.7% lower k. In 118 cases with CT available, FEV1%predicted and age remained associated with k (R2=0.24). Physical activity was not retained in any model.

Conclusions

Locomotor muscle oxidative capacity was positively associated with FEV1%predicted and negatively associated with age. Physical activity or radiographic COPD manifestations were not significantly associated with muscle oxidative impairment.

Contributions to forearm desaturation during transient ischemia in healthy adult males and females across the lifespan

This study investigated skeletal muscle tissue oxygenation (StO2) desaturation in males and females across the adult lifespan. One hundred-two individuals (51 females) of 41 young, 34 midlife, and 27 older adults completed a vascular occlusion test with near-infrared spectroscopy (NIRS + VOT). This included five minutes of arterial occlusion, inducing transient ischemia in the forearm flexor muscle group while recording StO2. The magnitude of desaturation (StO2mag) was quantified as the difference between baseline StO2 and the minimum StO2 value observed during ischemia. The rate of desaturation was also examined. Forearm adipose tissue thickness (ATT), forearm lean mass, and handgrip muscular strength were measured. A p ≤ 0.05 was considered significant. Two-way between factor Analysis of variance (ANOVAs) indicated that males exhibited significantly (p < 0.001) less ATT than females (collapsed across age) and that forearm lean mass (p < 0.001) and muscular strength (p < 0.001) decreased across the lifespan independent of sex. Bivariate analyses revealed significant (p < 0.05) associations for sex, age, ATT, forearm lean mass, and muscular strength with the desaturation metrics. The ATT values demonstrated the strongest relations with StO2mag and desaturation rate (r = -0.620 and 0.618). Using a model comparison approach, ATT plus age offered the best predictive power for StO2mag and desaturation rate (R2 = 0.456 and 0.438) such that the inclusion of sex did not improve the models. These findings suggested differences in desaturation were primarily explained by variations in ATT and, to a lesser extent, age, but biological sex had no meaningful effect. Future studies must determine what other factors influence desaturation during ischemia.

The Detrimental Effects of Bedrest: Premature Cardiovascular Aging and Dysfunction

Bedrest as an experimental paradigm or as an in-patient stay for medical reasons has negative consequences for cardiovascular health. The effects of severe inactivity parallel many of the changes experienced with natural aging but over a much shorter duration. Cardiac function is reduced, arteries stiffen, neural reflex responses are impaired, and metabolic and oxidative stress responses impose burden on the heart and vascular systems. The effect of these changes is revealed in studies of integrative function. Aerobic fitness progressively deteriorates with bedrest and tolerance of upright posture is rapidly impaired. In this review we consider the similarities of aging and bedrest-induced cardiovascular deconditioning. We concur with many recent clinical recommendations that early and regular mobility with upright posture will reduce likelihood of hospital-associated disability related to bedrest.

Muscle Mitochondrial Bioenergetic Capacities Are Associated With Multimorbidity Burden in Older Adults: The Study of Muscle, Mobility and Aging

BACKGROUND

The geroscience hypothesis posits that aging biological processes contribute to many age-related deficits, including the accumulation of multiple chronic diseases. Though only one facet of mitochondrial function, declines in muscle mitochondrial bioenergetic capacities may contribute to this increased susceptibility to multimorbidity.

METHODS

The Study of Muscle, Mobility and Aging (SOMMA) assessed ex vivo muscle mitochondrial energetics in 764 older adults (mean age = 76.4, 56.5% women, and 85.9% non-Hispanic White) by high-resolution respirometry of permeabilized muscle fibers. We estimated the proportional odds ratio (POR [95% CI]) for the likelihood of greater multimorbidity (4 levels: 0 conditions, N = 332; 1 condition, N = 299; 2 conditions, N = 98; or 3+ conditions, N = 35) from an index of 11 conditions, per SD decrement in muscle mitochondrial energetic parameters. Distribution of conditions allowed for testing the associations of maximal muscle energetics with some individual conditions.

RESULTS

Lower oxidative phosphorylation supported by fatty acids and/or complex I- and II-linked carbohydrates (eg, Max OXPHOSCI+CII) was associated with a greater multimorbidity index score (POR = 1.32 [1.13, 1.54]) and separately with diabetes mellitus (OR = 1.62 [1.26, 2.09]), depressive symptoms (OR = 1.45 [1.04, 2.00]) and possibly chronic kidney disease (OR = 1.57 [0.98, 2.52]) but not significantly with other conditions (eg, cardiac arrhythmia, chronic obstructive pulmonary disease).

CONCLUSIONS

Lower muscle mitochondrial bioenergetic capacities were associated with a worse composite multimorbidity index score. Our results suggest that decrements in muscle mitochondrial energetics may contribute to a greater global burden of disease and are more strongly related to some conditions than others.

MFN2 overexpression in skeletal muscles of young and old mice causes a mild hypertrophy without altering mitochondrial respiration and H2O2 emission

AIM

Sarcopenia, the aging-related loss of muscle mass and function, is a debilitating process negatively impacting the quality of life of affected individuals. Although the mechanisms underlying sarcopenia are incompletely understood, impairments in mitochondrial dynamics, including mitochondrial fusion, have been proposed as a contributing factor. However, the potential of upregulating mitochondrial fusion proteins to alleviate the effects of aging on skeletal muscles remains unexplored. We therefore hypothesized that overexpressing Mitofusin 2 (MFN2) in skeletal muscle in vivo would mitigate the effects of aging on muscle mass and improve mitochondrial function.

METHODS

MFN2 was overexpressed in young (7 mo) and old (24 mo) male mice for 4 months through intramuscular injections of an adeno-associated viruses. The impacts of MFN2 overexpression on muscle mass and fiber size (histology), mitochondrial respiration, and H2O2 emission (Oroboros fluororespirometry), and various signaling pathways (qPCR and western blotting) were investigated.

RESULTS

MFN2 overexpression increased muscle mass and fiber size in both young and old mice. No sign of fibrosis, necrosis, or inflammation was found upon MFN2 overexpression, indicating that the hypertrophy triggered by MFN2 overexpression was not pathological. MFN2 overexpression even reduced the proportion of fibers with central nuclei in old muscles. Importantly, MFN2 overexpression had no impact on muscle mitochondrial respiration and H2O2 emission in both young and old mice. MFN2 overexpression attenuated the increase in markers of impaired autophagy in old muscles.

CONCLUSION

MFN2 overexpression may be a viable approach to mitigate aging-related muscle atrophy and may have applications for other muscle disorders.

Human myofiber-enriched aging-induced lncRNA FRAIL1 promotes loss of skeletal muscle function

The loss of skeletal muscle mass during aging is a significant health concern linked to adverse outcomes in older individuals. Understanding the molecular basis of age-related muscle loss is crucial for developing strategies to combat this debilitating condition. Long noncoding RNAs (lncRNAs) are a largely uncharacterized class of biomolecules that have been implicated in cellular homeostasis and dysfunction across a many tissues and cell types. To identify lncRNAs that might contribute to skeletal muscle aging, we screened for lncRNAs whose expression was altered in vastus lateralis muscle from older compared to young adults. We identified FRAIL1 as an aging-induced lncRNA with high abundance in human skeletal muscle. In healthy young and older adults, skeletal muscle FRAIL1 was increased with age in conjunction with lower muscle function. Forced expression of FRAIL1 in mouse tibialis anterior muscle elicits a dose-dependent reduction in skeletal muscle fiber size that is independent of changes in muscle fiber type. Furthermore, this reduction in muscle size is dependent on an intact region of FRAIL1 that is highly conserved across non-human primates. Unbiased transcriptional and proteomic profiling of the effects of FRAIL1 expression in mouse skeletal muscle revealed widespread changes in mRNA and protein abundance that recapitulate age-related changes in pathways and processes that are known to be altered in aging skeletal muscle. Taken together, these findings shed light on the intricate molecular mechanisms underlying skeletal muscle aging and implicate FRAIL1 in age-related skeletal muscle phenotypes.

Lower muscle mitochondrial energetics is associated with greater phenotypic frailty in older women and men: the Study of Muscle, Mobility and Aging

BACKGROUND

Phenotypic frailty syndrome identifies older adults at greater risk for adverse health outcomes. Despite the critical role of mitochondria in maintaining cellular function, including energy production, the associations between muscle mitochondrial energetics and frailty have not been widely explored in a large, well-phenotyped, older population.

METHODS

The Study of Muscle, Mobility and Aging (SOMMA) assessed muscle energetics in older adults (N = 879, mean age = 76.3 years, 59.2% women). 31Phosporous magnetic resonance spectroscopy measured maximal production of adenosine triphosphate (ATPmax) in vivo, while ex vivo high-resolution respirometry of permeabilized muscle fibers from the vastus lateralis measured maximal oxygen consumption supported by fatty acids and complex I- and II-linked carbohydrates (e.g., Max OXPHOSCI+CII). Five frailty criteria, shrinking, weakness, exhaustion, slowness, and low activity, were used to classify participants as robust (0, N = 397), intermediate (1-2, N = 410), or frail (≥ 3, N = 66). We estimated the proportional odds ratio (POR) for greater frailty, adjusted for multiple potential confounders.

RESULTS

One-SD decrements of most respirometry measures (e.g., Max OXPHOSCI+CII, adjusted POR = 1.5, 95%CI [1.2,1.8], p = 0.0001) were significantly associated with greater frailty classification. The associations of ATPmax with frailty were weaker than those between Max OXPHOSCI+CII and frailty. Muscle energetics was most strongly associated with slowness and low physical activity components.

CONCLUSIONS

Our data suggest that deficits in muscle mitochondrial energetics may be a biological driver of frailty in older adults. On the other hand, we did observe differential relationships between measures of muscle mitochondrial energetics and the individual components of frailty.

Metabolomic response to acute resistance exercise in healthy older adults by 1H-NMR

BACKGROUND

The favorable health-promoting adaptations to exercise result from cumulative responses to individual bouts of physical activity. Older adults often exhibit anabolic resistance; a phenomenon whereby the anabolic responses to exercise and nutrition are attenuated in skeletal muscle. The mechanisms contributing to age-related anabolic resistance are emerging, but our understanding of how chronological age influences responsiveness to exercise is incomplete. The objective was to determine the effects of healthy aging on peripheral blood metabolomic response to a single bout of resistance exercise and whether any metabolites in circulation are predictive of anabolic response in skeletal muscle.

METHODS

Thirty young (20-35 years) and 49 older (65-85 years) men and women were studied in a cross-sectional manner. Participants completed a single bout of resistance exercise consisting of eight sets of 10 repetitions of unilateral knee extension at 70% of one-repetition maximum. Blood samples were collected before exercise, immediately post exercise, and 30-, 90-, and 180-minutes into recovery. Proton nuclear magnetic resonance spectroscopy was used to profile circulating metabolites at all timepoints. Serial muscle biopsies were collected for measuring muscle protein synthesis rates.

RESULTS

Our analysis revealed that one bout of resistance exercise elicits significant changes in 26 of 33 measured plasma metabolites, reflecting alterations in several biological processes. Furthermore, 12 metabolites demonstrated significant interactions between exercise and age, including organic acids, amino acids, ketones, and keto-acids, which exhibited distinct responses to exercise in young and older adults. Pre-exercise histidine and sarcosine were negatively associated with muscle protein synthesis, as was the pre/post-exercise fold change in plasma histidine.

CONCLUSIONS

This study demonstrates that while many exercise-responsive metabolites change similarly in young and older adults, several demonstrate age-dependent changes even in the absence of evidence of sarcopenia or frailty.

TRIAL REGISTRATION

Clinical trial registry: ClinicalTrials.gov NCT03350906.

Muscle mitochondrial bioenergetic capacities is associated with multimorbidity burden in older adults: the Study of Muscle, Mobility and Aging (SOMMA)

Background

The geroscience hypothesis posits that aging biological processes contribute to many age-related deficits, including the accumulation of multiple chronic diseases. Though only one facet of mitochondrial function, declines in muscle mitochondrial bioenergetic capacities may contribute to this increased susceptibility to multimorbidity.

Methods

The Study of Muscle, Mobility and Aging (SOMMA) assessed ex vivo muscle mitochondrial energetics in 764 older adults (mean age =76.4, 56.5% women, 85.9% non-Hispanic white) by high-resolution respirometry of permeabilized muscle fibers. We estimated the proportional odds ratio (POR [95%CI]) for the likelihood of greater multimorbidity (four levels: 0 conditions, N=332; 1 condition, N=299; 2 conditions, N=98; or 3+ conditions, N=35) from an index of 11 conditions, per SD decrement in muscle mitochondrial energetic parameters. Distribution of conditions allowed for testing the associations of maximal muscle energetics with some individual conditions.

Results

Lower oxidative phosphorylation supported by fatty acids and/or complex-I and -II linked carbohydrates (e.g., Max OXPHOSCI+CII) was associated with a greater multimorbidity index score (POR=1.32[1.13,1.54]) and separately with diabetes mellitus (OR=1.62[1.26,2.09]), depressive symptoms (OR=1.45[1.04,2.00]) and possibly chronic kidney disease (OR=1.57[0.98,2.52]) but not significantly with other conditions (e.g., cardiac arrhythmia, chronic obstructive pulmonary disease).

Conclusions

Lower muscle mitochondrial bioenergetic capacities was associated with a worse composite multimorbidity index score. Our results suggest that decrements in muscle mitochondrial energetics may contribute to a greater global burden of disease and is more strongly related to some conditions than others.

Estimated standard values of aerobic capacity according to sex and age in a Japanese population: A scoping review

Aerobic capacity is a fitness measure reflecting the ability to sustain whole-body physical activity as fast and long as possible. Identifying the distribution of aerobic capacity in a population may help estimate their health status. This study aimed to estimate standard values of aerobic capacity (peak oxygen uptake [Formula: see text] and anaerobic threshold [AT]/kg) for the Japanese population stratified by sex and age using a meta-analysis. Moreover, the comparison of the estimated standard values of the Japanese with those of other populations was performed as a supplementary analysis. We systematically searched original articles on aerobic capacity in the Japanese population using PubMed, Ichushi-Web, and Google Scholar. We meta-analysed [Formula: see text] (total: 78,714, men: 54,614, women: 24,100) and AT (total: 4,042, men: 1,961, women: 2,081) data of healthy Japanese from 21 articles by sex and age. We also searched, collected and meta-analysed data from other populations. Means and 95% confidence intervals were calculated. The estimated standard values of [Formula: see text] (mL/kg/min) for Japanese men and women aged 4-9, 10-19, 20-29, 30-39, 40-49, 50-59, 60-69, and 70-79 years were 47.6, 51.2, 43.2, 37.2, 34.5, 31.7, 28.6, and 26.3, and 42.0, 43.2, 33.6, 30.6, 27.4, 25.6, 23.4, and 23.1, respectively. The AT/kg (mL/kg/min) for Japanese men and women aged 20-29, 30-39, 40-49, 50-59, 60-69, and 70-79 years were 21.1, 18.3, 16.8, 15.9, 15.8, and 15.2, and 17.4, 17.0, 15.7, 15.0, 14.5, and 14.2, respectively. Herein, we presented the estimated standard values of aerobic capacity according to sex and age in a Japanese population. In conclusion, aerobic capacity declines with ageing after 20-29 years of age. Additionally, aerobic capacity is lower in the Japanese population than in other populations across a wide range of age groups. Standard value estimation by meta-analysis can be conducted in any country or region and for public health purposes.

Mitochondrial Energetics in Skeletal Muscle Are Associated With Leg Power and Cardiorespiratory Fitness in the Study of Muscle, Mobility and Aging

BACKGROUND

Mitochondrial energetics are an important property of aging muscle, as generation of energy is pivotal to the execution of muscle contraction. However, its association with functional outcomes, including leg power and cardiorespiratory fitness, is largely understudied.

METHODS

In the Study of Muscle, Mobility, and Aging, we collected vastus lateralis biopsies from older adults (n = 879, 70-94 years, 59.2% women). Maximal State 3 respiration (Max OXPHOS) was assessed in permeabilized fiber bundles by high-resolution respirometry. Capacity for maximal adenosine triphosphate production (ATPmax) was measured in vivo by 31P magnetic resonance spectroscopy. Leg extension power was measured with a Keiser press system, and VO2 peak was determined using a standardized cardiopulmonary exercise test. Gender-stratified multivariate linear regression models were adjusted for age, race, technician/site, adiposity, and physical activity with beta coefficients expressed per 1-SD increment in the independent variable.

RESULTS

Max OXPHOS was associated with leg power for both women (β = 0.12 Watts/kg, p < .001) and men (β = 0.11 Watts/kg, p < .050). ATPmax was associated with leg power for men (β = 0.09 Watts/kg, p < .05) but was not significant for women (β = 0.03 Watts/kg, p = .11). Max OXPHOS and ATPmax were associated with VO2 peak in women and men (Max OXPHOS, β women = 1.03 mL/kg/min, β men = 1.32 mL/kg/min; ATPmax β women = 0.87 mL/kg/min, β men = 1.50 mL/kg/min; all p < .001).

CONCLUSIONS

Higher muscle mitochondrial energetics measures were associated with both better cardiorespiratory fitness and greater leg power in older adults. Muscle mitochondrial energetics explained a greater degree of variance in VO2 peak compared to leg power.

Exercise and ageing impact the kynurenine/tryptophan pathway and acylcarnitine metabolite pools in skeletal muscle of older adults

Exercise-induced perturbation of skeletal muscle metabolites is a probable mediator of long-term health benefits in older adults. Although specific metabolites have been identified to be impacted by age, physical activity and exercise, the depth of coverage of the muscle metabolome is still limited. Here, we investigated resting and exercise-induced metabolite distribution in muscle from well-phenotyped older adults who were active or sedentary, and a group of active young adults. Percutaneous biopsies of the vastus lateralis were obtained before, immediately after and 3 h following a bout of endurance cycling. Metabolite profile in muscle biopsies was determined by tandem mass spectrometry. Mitochondrial energetics in permeabilized fibre bundles was assessed by high resolution respirometry and fibre type proportion was assessed by immunohistology. We found that metabolites of the kynurenine/tryptophan pathway were impacted by age and activity. Specifically, kynurenine was elevated in muscle from older adults, whereas downstream metabolites of kynurenine (kynurenic acid and NAD+ ) were elevated in muscle from active adults and associated with cardiorespiratory fitness and muscle oxidative capacity. Acylcarnitines, a potential marker of impaired metabolic health, were elevated in muscle from physically active participants. Surprisingly, despite baseline group difference, acute exercise-induced alterations in whole-body substrate utilization, as well as muscle acylcarnitines and ketone bodies, were remarkably similar between groups. Our data identified novel muscle metabolite signatures that associate with the healthy ageing phenotype provoked by physical activity and reveal that the metabolic responsiveness of muscle to acute endurance exercise is retained [NB]:AUTHOR: Please ensure that the appropriate material has been provide for Table S2, as well as for Figures S1 to S7, as also cited in the text with age regardless of activity levels. KEY POINTS: Kynurenine/tryptophan pathway metabolites were impacted by age and physical activity in human muscle, with kynurenine elevated in older muscle, whereas downstream products kynurenic acid and NAD+ were elevated in exercise-trained muscle regardless of age. Acylcarnitines, a marker of impaired metabolic health when heightened in circulation, were elevated in exercise-trained muscle of young and older adults, suggesting that muscle act as a metabolic sink to reduce the circulating acylcarnitines observed with unhealthy ageing. Despite the phenotypic differences, the exercise-induced response of various muscle metabolite pools, including acylcarnitine and ketone bodies, was similar amongst the groups, suggesting that older adults can achieve the metabolic benefits of exercise seen in young counterparts.

Effects of Combined Inorganic Nitrate and Nitrite Supplementation on Cardiorespiratory Fitness and Skeletal Muscle Oxidative Capacity in Type 2 Diabetes: A Pilot Randomized Controlled Trial

Nitric oxide (NO) stimulates mitochondrial biogenesis in skeletal muscle. However, NO metabolism is disrupted in individuals with type 2 diabetes mellitus (T2DM) potentially contributing to their decreased cardiorespiratory fitness (i.e., VO2max) and skeletal muscle oxidative capacity. We used a randomized, double-blind, placebo-controlled, 8-week trial with beetroot juice containing nitrate (NO3−) and nitrite (NO2−) (250 mg and 20 mg/day) to test potential benefits on VO2max and skeletal muscle oxidative capacity in T2DM. T2DM (N = 36, Age = 59 ± 9 years; BMI = 31.9 ± 5.0 kg/m2) and age- and BMI-matched non-diabetic controls (N = 15, Age = 60 ± 9 years; BMI = 29.5 ± 4.6 kg/m2) were studied. Mitochondrial respiratory capacity was assessed in muscle biopsies from a subgroup of T2DM and controls (N = 19 and N = 10, respectively). At baseline, T2DM had higher plasma NO3− (100%; p < 0.001) and lower plasma NO2− levels (−46.8%; p < 0.0001) than controls. VO2max was lower in T2DM (−26.4%; p < 0.001), as was maximal carbohydrate- and fatty acid-supported oxygen consumption in permeabilized muscle fibers (−26.1% and −25.5%, respectively; p < 0.05). NO3−/NO2− supplementation increased VO2max (5.3%; p < 0.01). Further, circulating NO2−, but not NO3−, positively correlated with VO2max after supplementation (R2= 0.40; p < 0.05). Within the NO3−/NO2− group, 42% of subjects presented improvements in both carbohydrate- and fatty acid-supported oxygen consumption in skeletal muscle (vs. 0% in placebo; p < 0.05). VO2max improvements in these individuals tended to be larger than in the rest of the NO3−/NO2− group (1.21 ± 0.51 mL/(kg*min) vs. 0.31 ± 0.10 mL/(kg*min); p = 0.09). NO3−/NO2− supplementation increases VO2max in T2DM individuals and improvements in skeletal muscle oxidative capacity appear to occur in those with more pronounced increases in VO2max.

A Randomized Trial of the Effects of Dietary n3-PUFAs on Skeletal Muscle Function and Acute Exercise Response in Healthy Older Adults

Skeletal muscle is critical for maintaining mobility, independence, and metabolic health in older adults. However, a common feature of aging is the progressive loss of skeletal muscle mass and function, which is often accompanied by mitochondrial impairments, oxidative stress, and insulin resistance. Exercise improves muscle strength, mitochondrial health, and cardiorespiratory fitness, but older adults often exhibit attenuated anabolic responses to acute exercise. Chronic inflammation associated with aging may contribute to this "anabolic resistance" and therapeutic interventions that target inflammation may improve exercise responsiveness. To this end, we conducted a randomized controlled trial to determine the effect of 6 months of dietary omega-3 polyunsaturated fatty acids (n3-PUFA) supplementation on skeletal muscle function (mass, strength), mitochondrial physiology (respiration, ATP production, ROS generation), and acute exercise responsiveness at the level of the muscle (fractional synthesis rate) and the whole-body (amino acid kinetics) in healthy older adults. When compared with a corn oil placebo (n = 33; 71.5 ± 4.8 years), older adults treated with 4 g/day n3-PUFA (n = 30; 71.4 ± 4.5 years) exhibited modest but significant increases in muscle strength (3.1 ± 14.7% increase in placebo vs. 7.5 ± 14.1% increase in n3-PUFA; p = 0.039). These improvements in muscle strength with n3-PUFA supplementation occurred in the absence of any effects on mitochondrial function and a minor attenuation of the acute response to exercise compared to placebo. Together, these data suggest modest benefits of dietary n3-PUFAs to muscle function in healthy older adults. Future studies may elucidate whether n3-PUFA supplementation improves the exercise response in elderly individuals with co-morbidities, such as chronic inflammatory disease or sarcopenia.

Metabolic changes in aging humans: current evidence and therapeutic strategies

Aging and metabolism are inextricably linked, and many age-related changes in body composition, including increased central adiposity and sarcopenia, have underpinnings in fundamental aging processes. These age-related changes are further exacerbated by a sedentary lifestyle and can be in part prevented by maintenance of activity with aging. Here we explore the age-related changes seen in individual metabolic tissues - adipose, muscle, and liver - as well as globally in older adults. We also discuss the available evidence for therapeutic interventions such as caloric restriction, resistance training, and senolytic and senomorphic drugs to maintain healthy metabolism with aging, focusing on data from human studies.