The Study of Muscle, Mobility and Aging (SOMMA): A Unique Cohort Study About the Cellular Biology of Aging and Age-related Loss of Mobility

Sex differences in the association between skeletal muscle energetics and perceived physical fatigability: the Study of Muscle, Mobility and Aging (SOMMA)

Greater perceived physical fatigability and lower skeletal muscle energetics are both predictors of mobility decline. Characterizing associations between muscle energetics and perceived fatigability may provide insight into potential targets to prevent mobility decline. We examined associations of in vivo (maximal ATP production, ATPmax) and ex vivo (maximal carbohydrate supported oxidative phosphorylation [max OXPHOS] and maximal fatty acid supported OXPHOS [max FAO OXPHOS]) measures of mitochondrial energetics with two measures of perceived physical fatigability, Pittsburgh Fatigability Scale (PFS, 0-50, higher = greater) and Rating of Perceived Exertion (RPE Fatigability, 6-20, higher = greater) after a slow treadmill walk. Participants from the Study of Muscle, Mobility and Aging (N = 873) were 76.3 ± 5.0 years old, 59.2% women, and 85.3% White. Higher muscle energetics (both in vivo and ex vivo) were associated with lower perceived physical fatigability, all p < 0.03. When stratified by sex, higher ATPmax was associated with lower PFS Physical for men only; higher max OXPHOS and max FAO OXPHOS were associated with lower RPE Fatigability for both sexes. Higher skeletal muscle energetics were associated with 40-55% lower odds of being in the most (PFS ≥ 25, RPE Fatigability ≥ 12) vs least (PFS 0-4, RPE Fatigability 6-7) severe fatigability strata, all p < 0.03. Being a woman was associated with 2-3 times higher odds of being in the most severe fatigability strata when controlling for ATPmax but not the ex vivo measures (p < 0.05). Better mitochondrial energetics were linked to lower fatigability and less severe fatigability in older adults. Findings imply that improving skeletal muscle energetics may mitigate perceived physical fatigability and prolong healthy aging.

Nigrostriatal dopaminergic integrity in relation to prefrontal cortex activity and gait performance during dual-task walking in older adults

Greater walking automaticity facilitates maintenance of gait speed without prefrontal cortex (PFC) resources. Brain aging may cause shifts to more attentional gait with greater engagement of the PFC. Nigrostriatal dopaminergic integrity likely facilitates walking automaticity and maintenance of gait speed during attentional dual-tasks. Older adults (n=201; age=74.9; 63.2% women, gait speed=1.10 m/s) completed a dual-task protocol of saying every other letter of the alphabet while walking. PFC activation was measured by functional near-infrared spectroscopy. Four groups were defined based on PFC activation (increased during dual-task, PFC+, or not, PFC-) and gait speed performance (maintained during dual-task, gait+, or slowed, gait-). To compare nigrostriatal dopaminergic integrity across groups, we assessed binding of the type-2 vesicular monoamine transporter (VMAT2) density in the sensorimotor and associative striatum using [11C]-(+)-α-dihydrotetrabenazine (DTBZ) positron emission tomography. Multinomial regression estimated adjusted associations of DTBZ binding with group membership. We hypothesized that DTBZ binding was highest for those who maintained gait speed without additional PFC activation when switching from single- to dual-task (PFC-/gait+; i.e., highest gait automaticity). In bivariate analyses, the PFC-/gait+ group had the highest DTBZ binding in the sensorimotor striatum (p=0.05); binding in the associative striatum was similar across groups (p=0.1). Results were similar in adjusted regression analyses; DTBZ binding in sensorimotor striatum was associated with lower likelihood to be in the PFC-/gait- (OR=0.28; 95% CI: 0.08, 0.94) or the PFC+/gait+ (OR=0.29; 95% CI: 0.10, 0.84) groups compared to PFC-/gait+ reference group. These results provide support for dopaminergic involvement in sustaining gait automaticity at older ages.

Molecular mechanisms and potential interventions during aging-associated sarcopenia

Sarcopenia, a common condition observed in the elderly, presenting a significant public health challenge due to its high prevalence, insidious onset and diverse systemic effects. Despite ongoing research, the precise etiology of sarcopenia remains elusive. Aging-related processes, which included inflammation, oxidative stress, compromised mitochondrial function and apoptosis, have been implicated in its development. Notably, effective pharmacological treatments for sarcopenia are currently lacking, highlighting the necessity for a deeper understanding of its pathogenesis and causative factors to enable proactive interventions. This article is aimed to provide an extensive overview of the pathogenesis of sarcopenia, along with a summary of current treatment and prevention strategies.

Cerebral Metabolic Rate of Oxygen and Accelerometry-Based Fatigability in Community-Dwelling Older Adults

Alterations in energy metabolism may drive fatigue in older age, but prior research primarily focused on skeletal muscle energetics without assessing other systems, and utilized self-reported measures of fatigue. We tested the association between energy metabolism in the brain and an objective measure of fatigability in the Study of Muscle, Mobility and Aging (N=119, age 76.8±4.0 years, 59.7% women). Total brain cerebral metabolic rate of oxygen (CMRO 2 ) was measured using arterial spin labeling and T 2 -relaxation under spin tagging MRI protocols. Accelerometry-based fatigability status during a fast-paced 400m walk was determined using the Pittsburgh Fatigability Index (PPFI, higher=worse). Confounders included skeletal muscle energetics, measured in vivo using spectroscopy and ex vivo using respirometry, cardiorespiratory fitness (VO 2 peak), weight, medication count, and multimorbidity. Multivariable logistic regression models were used to estimate the association (odds ratio (OR)) of CMRO 2 with PPFI>0 compared to the referent group PPFI=0. Models were first adjusted for age and sex, and further adjusted for confounders. In this sample, 41.2% had PPFI>0 (median 3.3% [0.4-8.0%]). CMRO 2 was positively associated with PPFI>0 (age and sex adjusted OR=1.61, 95% CI: 1.06, 2.45, p=0.03); adjustment for confounders attenuated the association. The positive association of brain energetics and fatigability warrants further study in older adults.

MicroRNA signatures of VO 2 peak in older adult participants of the Study of Muscle, Mobility and Aging

Background

Peak oxygen consumption during exercise (VO 2 peak), is a direct measure of cardiorespiratory fitness (CF), a key indicator of physical function and overall health. However, the molecular changes that underpin VO 2 peak variation are not clear. Our objective is to understand the miRNA signatures that relate to VO 2 peak variation, which could provide insights to novel mechanisms that contribute to low VO 2 peak.

Methods

We used small RNA sequencing to analyze serum samples from 72 participants (70-79 yrs old, 53% female) of the Study of Muscle, Mobility and Aging (SOMMA). We analyzed samples from individuals with low or high VO 2 peak (N=18/group) as well as samples from 36 randomly selected participants spanning the entire spectrum of VO 2 peak. We used LIMMA analysis package for regression analysis and to identify differentially expressed miRNAs. We used receiver operating characteristic curve analysis to evaluate the Area Under the Curve (AUC) and sensitivity and specificity rates.

Results

We identified 1,055 miRNAs expressed in all serum samples. Expression of 65 miRNAs differed between participants with low and high VO 2 peak (p < 0.05). After p-value adjustment, expression of 5 miRNAs (miR-1301-3p, -431-5p, -501-5p, -519a-3p, and -18a-3p) remained significantly different (FDR = 0.05). The five miRNAs had AUC ranging from 0.77 to 0.84. The optimal sensitivity and specificity ranged from 70 to 80% and 80 to 90%, respectively. After adjustment for age and sex covariates, 46 miRNAs significantly correlated with VO 2 peak (p < 0.05) and miR-519a-3p remained significant based on adjusted of p-values.

Conclusions

We identified a miRNA signature of VO 2 peak in older individuals that might provide insights to novel mechanisms that drive low VO 2 peak. Future studies will validate the findings in a larger, longitudinal study cohort.

Higher skeletal muscle mitochondrial oxidative capacity is associated with preserved brain structure up to over a decade

Impaired muscle mitochondrial oxidative capacity is associated with future cognitive impairment, and higher levels of PET and blood biomarkers of Alzheimer's disease and neurodegeneration. Here, we examine its associations with up to over a decade-long changes in brain atrophy and microstructure. Higher in vivo skeletal muscle oxidative capacity via MR spectroscopy (post-exercise recovery rate, kPCr) is associated with less ventricular enlargement and brain aging progression, and less atrophy in specific regions, notably primary sensorimotor cortex, temporal white and gray matter, thalamus, occipital areas, cingulate cortex, and cerebellum white matter. Higher kPCr is also associated with less microstructural integrity decline in white matter around cingulate, including superior longitudinal fasciculus, corpus callosum, and cingulum. Higher in vivo muscle oxidative capacity is associated with preserved brain structure up to over a decade, particularly in areas important for cognition, motor function, and sensorimotor integration.

Skeletal Muscle Composition, Power, and Mitochondrial Energetics in Older Men and Women With Knee Osteoarthritis

OBJECTIVE

Our objective was to investigate the overall and sex-specific relationships between the presence and severity of knee osteoarthritis (KOA) and muscle composition, power, and energetics in older adults.

METHODS

Male and female patients (n = 655, mean ± SD age 76.1 ± 4.9 years; 57% female) enrolled in the Study of Muscle, Mobility, and Aging completed standing knee radiographs and knee pain assessments. Participants were divided into three groups using Kellgren-Lawrence grade (KLG) of KOA severity (0-1, 2, or 3-4). Outcome measures included whole-body muscle mass, thigh fat-free muscle (FFM) volume and muscle fat infiltration (MFI), leg power, specific power (power normalized to muscle volume), and muscle mitochondrial energetics.

RESULTS

Overall, the presence and severity of KOA is associated with greater MFI, lower leg power and specific power, and reduced oxidative phosphorylation (P trend < 0.036). Sex-specific analysis revealed reduced energetics only in female patients with KOA (P trend < 0.007) compared to female patients without KOA. In models adjusted for age, sex, race, nonsteroidal anti-inflammatory drug administration, site or technician, physical activity, height, and participants with abdominal adiposity with KLG 3 to 4 had greater MFI (mean 0.008%, 95% confidence interval [CI] 0.004%-0.011%) and lower leg power (mean -51.56 W, 95% CI -74.03 to -29.10 W) and specific power (mean -5.38 W/L, 95% CI -7.31 to -3.45 W/L) than those with KLG 0 to 1. No interactions were found between pain and KLG status. Among those with KOA, MFI and oxidative phosphorylation were associated with thigh FFM volume, leg power, and specific power.

CONCLUSION

Muscle health is associated with the presence and severity of KOA and differs by sex. Although muscle composition and power are lower in both male and female patients with KOA, regardless of pain status, mitochondrial energetics is reduced only in female patients.

Muscle aging and sarcopenia: The pathology, etiology, and most promising therapeutic targets

Sarcopenia is a progressive muscle wasting disorder that severely impacts the quality of life of elderly individuals. Although the natural aging process primarily causes sarcopenia, it can develop in response to other conditions. Because muscle function is influenced by numerous changes that occur with age, the etiology of sarcopenia remains unclear. However, recent characterizations of the aging muscle transcriptional landscape, signaling pathway disruptions, fiber and extracellular matrix compositions, systemic metabolomic and inflammatory responses, mitochondrial function, and neurological inputs offer insights and hope for future treatments. This review will discuss age-related changes in healthy muscle and our current understanding of how this can deteriorate into sarcopenia. As our elderly population continues to grow, we must understand sarcopenia and find treatments that allow individuals to maintain independence and dignity throughout an extended lifespan.

Higher Striatal Dopamine is Related With Lower Physical Performance Fatigability in Community-Dwelling Older Adults

BACKGROUND

Fatigability in community-dwelling older adults is highly prevalent and disabling, but lacks a treatment. Greater nigrostriatal dopaminergic signaling can ameliorate performance fatigability in healthy young adults, but its role in community-dwelling older adults is not known. We hypothesized that higher nigrostriatal dopaminergic integrity would be associated with lower performance fatigability, independent of cardiopulmonary and musculoskeletal energetics and other health conditions.

METHODS

In 125 older adults participating in the Study of Muscle, Mobility and Aging, performance fatigability was measured as performance deterioration during a fast 400 m walk (% slowing down from the 2nd to the 9th lap). Nigrostriatal DA integrity was measured using (+)-[11C] dihydrotetrabenazine (DTBZ) PET imaging. The binding signal was obtained separately for the subregions regulating sensorimotor (posterior putamen), reward (ventral striatum), and executive control processes (dorsal striatum). Multivariable linear regression models of performance fatigability (dependent variable) estimated the coefficients of dopamine integrity in striatal subregions, adjusted for demographics, comorbidities, and cognition. Models were further adjusted for skeletal muscle energetics (via biopsy) and cardiopulmonary fitness (via cardiopulmonary exercise testing).

RESULTS

Higher [11C]-DTBZ binding in the posterior putamen was significantly associated with lower performance fatigability (demographic-adjusted standardized β = -1.08, 95% CI: -1.96, -0.20); results remained independent of adjustment for other covariates, including cardiopulmonary and musculoskeletal energetics. Associations with other striatal subregions were not significant.

DISCUSSION

Dopaminergic integrity in the sensorimotor striatum may influence performance fatigability in older adults without clinically overt diseases, independent of other aging systems.

Greater recalled pain and movement-evoked pain are associated with longer 400-meter walk and repeat stair climb time: the Study of Muscle, Mobility and Aging

Background

Musculoskeletal pain frequently accompanies the development of mobility disability and falls in old age. To better understand this, we aimed to quantify the impact of different pain measures-recalled pain and movement-evoked pain-on 400-meter walk and stair climb time in older adults participating in the Study of Muscle, Mobility and Aging (SOMMA).

Methods

In SOMMA (N=879, age=76.3 ± 5.0 years, 59% women, 84% Non-Hispanic White), participants completed usual pace 400m walk (avg=6.6 ± 1.2 min.) and repeat stair climb tests (avg=26.6 ± 7.2 sec.). Assessments of recalled pain included the Brief Pain Inventory short form (BPI-sf), total lower body pain (lower back, hips, knees, feet/ankles), stiffness (hip or knee), and Neuropathy Total Symptom Score (NTSS-6). Movement-evoked pain was assessed separately before and after the 400m walk and repeat stair climb tasks. Multivariable linear regression modeled the associations of pain with time to complete the tasks, reported as β[95%CI] expressed per SD increment of pain measure or β[95%CI] per pain categories, adjusted for age, sex, race, ethnicity, body mass index, prescription medications, and depressive symptoms.

Results

Greater degree of any pain measure was associated with longer physical performance time, though intercorrelations between recalled pain measures varied (r=0.13-0.57, p<0.05 for all). For each SD increment in lower body pain, participants had longer walk time (by 10.5 sec [6.1, 14.8]) and stair climb (by 0.6 sec [0.1, 1.1]). Compared to participants with no change in pain upon movement, walk time was longer in those with more pain upon movement (19.5 sec [10.3, 28.7]) (p<0.001) but not those with less pain upon movement; stair climb showed similar patterns.

Conclusions

Recalled and movement-evoked pain measures were weakly correlated with one another but similarly associated with time to complete 400m walk and stair climb tests. Different pain assessments capture different functional domains of pain but have similar associations with physical performance in these older adults.

Sarcopenia

Sarcopenia is the accelerated loss of skeletal muscle mass and function commonly, but not exclusively, associated with advancing age. It is observed across many species including humans in whom it can lead to decline in physical function and mobility as well as to increased risk of adverse outcomes including falls, fractures and premature mortality. Although prevalence estimates vary because sarcopenia has been defined in different ways, even using a conservative approach, the prevalence is between 5% and 10% in the general population. A life course framework has been proposed for understanding not only the occurrence of sarcopenia in later life but also influences operating at earlier life stages with potentially important implications for preventive strategies. Harnessing progress in understanding the hallmarks of ageing has been key to understanding sarcopenia pathophysiology. Considerable convergence in approaches to diagnosis of sarcopenia has occurred over the last 10 years, with a growing emphasis on the central importance of muscle strength. Resistance exercise is currently the mainstay of treatment; however, it is not suitable for all. Hence, adjunctive and alternative treatments to improve quality of life are needed. An internationally agreed approach to definition and diagnosis will enable a step change in the field and is likely to be available in the near future through the Global Leadership Initiative in Sarcopenia.

Role of Walking Energetics and Perceived Fatigability Differs by Gait Speed: The Study of Muscle, Mobility and Aging (SOMMA)

BACKGROUND

Slower gait speed may be driven by greater energy deficits and fatigability among older adults. We examined associations of walking energetics and perceived physical fatigability with gait speed among slower and faster walkers. Additionally, we used statistical mediation to examine the role of fatigability in the associations of walking energetics and gait speed using the Study of Muscle, Mobility and Aging (SOMMA).

METHODS

Perceived physical fatigability was assessed using the Pittsburgh Fatigability Scale (PFS) Physical score (range 0-50, higher = greater). A 3-phase cardiopulmonary exercise treadmill test collected peak oxygen consumption (VO2peak, mL/kg/min), energetic cost of walking (ECW, mL/kg/m), and cost-capacity ratio (VO2/VO2peak*100, %). Slower (<1.01 m/s) versus faster (≥1.01 m/s) walkers were classified using median 4-m gait speed. Linear regressions and statistical mediation analyses were conducted.

RESULTS

Slower walkers had lower VO2peak, higher ECW at preferred walking speed (PWS), and greater PFS Physical score compared to faster walkers (all p < .05; N = 849). One standard deviation (1-SD) higher VO2peak was associated with 0.1 m/s faster gait speed, while 1-SD higher ECW PWS, cost-capacity ratio at PWS and slow walking speed (SWS), and PFS Physical score were associated with 0.02-0.23 m/s slower gait speed. PFS Physical score was a significant statistical mediator in the associations between VO2peak (15.2%), SWS cost-capacity ratio (15.9%), and ECW PWS (10.7%) with gait speed and was stronger among slower walkers.

CONCLUSIONS

Slower walkers may be more influenced by perceptions of fatigue in addition to walking energetics. Our work highlights the importance of targeting both energetics and perceived fatigability to prevent mobility decline.

Cardiopulmonary Exercise Testing in a Prospective Multicenter Cohort of Older Adults

PURPOSE

Cardiorespiratory fitness (CRF) measured by peak oxygen consumption (V̇O 2peak ) declines with aging and correlates with mortality and morbidity. Cardiopulmonary exercise testing (CPET) is the criterion method to assess CRF, but its feasibility, validity, and reliability in older adults are unclear. Our objective was to design and implement a dependable, safe, and reliable CPET protocol in older adults.

METHODS

V̇O 2peak was measured by CPET, performed using treadmill exercise in 875 adults ≥70 yr in the Study of Muscle, Mobility and Aging (SOMMA). The protocol included a symptom-limited peak (maximal) exercise and two submaximal walking speeds. An adjudication process was in place to review tests for validity if they met any prespecified criteria (V̇O 2peak <12.0 mL·kg -1 ·min -1 ; maximum heart rate <100 bpm; respiratory exchange ratio <1.05 and a rating of perceived exertion <15). A subset ( N = 30) performed a repeat test to assess reproducibility.

RESULTS

CPET was safe and well tolerated, with 95.8% of participants able to complete the V̇O 2peak phase of the protocol. Only 56 (6.4%) participants had a risk alert and only two adverse events occurred: a fall and atrial fibrillation. Mean ± SD V̇O 2peak was 20.2 ± 4.8 mL·kg -1 ·min -1 , peak heart rate 142 ± 18 bpm, and peak respiratory exchange ratio 1.14 ± 0.09. Adjudication was indicated in 47 tests; 20 were evaluated as valid and 27 as invalid (18 data collection errors, 9 did not reach V̇O 2peak ). Reproducibility of V̇O 2peak was high (intraclass correlation coefficient = 0.97).

CONCLUSIONS

CPET was feasible, effective, and safe for older adults, including many with multimorbidity or frailty. These data support a broader implementation of CPET to provide insight into the role of CRF and its underlying determinants of aging and age-related conditions.

Associations of accelerometry-measured and self-reported physical activity and sedentary behavior with skeletal muscle energetics: The Study of Muscle, Mobility and Aging (SOMMA)

BACKGROUND

Skeletal muscle energetics decline with age, and physical activity (PA) has been shown to offset these declines in older adults. Yet, many studies reporting these effects were based on self-reported PA or structured exercise interventions. Therefore, we examined the associations of accelerometry-measured and self-reported PA and sedentary behavior (SB) with skeletal muscle energetics and explored the extent to which PA and sedentary behavior would attenuate the associations of age with muscle energetics.

METHODS

As part of the Study of Muscle, Mobility and Aging, enrolled older adults (n = 879), 810 (age = 76.4 ± 5.0 years old, mean ± SD; 58% women) had maximal muscle oxidative capacity measured ex vivo via high-resolution respirometry of permeabilized myofibers (maximal oxidative phosphorylation (maxOXPHOS)) and in vivo by 31phosphorus magnetic resonance spectroscopy (maximal adenosine triphosphate (ATPmax)). Accelerometry-measured sedentary behavior, light activity, and moderate-to-vigorous PA (MVPA) were assessed using a wrist-worn ActiGraph GT9X over 7 days. Self-reported sedentary behavior, MVPA, and all PA were assessed with the Community Healthy Activities Model Program for Seniors (CHAMPS) questionnaire. Linear regression models with progressive covariate adjustments evaluated the associations of sedentary behavior and PA with muscle energetics, as well as the attenuation of the age/muscle energetics association by MVPA and sedentary behavior. As a sensitivity analysis, we also examined activPAL-measured daily step count and time spent in sedentary behavior and their associations with muscle energetics.

RESULTS

Every 30 min/day more of ActiGraph-measured MVPA was associated with 0.65 pmol/(s × mg) higher maxOXPHOS and 0.012 mM/s higher ATPmax after adjusting for age, site/technician, and sex (p < 0.05). Light activity was not associated with maxOXPHOS or ATPmax. Meanwhile, every 30 min/day spent in ActiGraph-measured sedentary behavior was associated with 0.39 pmol/s × mg lower maxOXPHOS and 0.006 mM/s lower ATPmax (p < 0.05). Only associations with ATPmax held after further adjusting for socioeconomic status, body mass index, lifestyle factors, and multimorbidity. CHAMPS MVPA and all PA yielded similar associations with maxOXPHOS and ATPmax (p < 0.05), but sedentary behavior did not. Higher activPAL step count was associated with higher maxOXHPOS and ATPmax (p < 0.05), but time spent in sedentary behavior was not. Additionally, age was significantly associated with muscle energetics for men only (p < 0.05); adjusting for time spent in ActiGraph-measured MVPA attenuated the age association with ATPmax by 58% in men.

CONCLUSION

More time spent in accelerometry-measured or self-reported daily PA, especially MVPA, was associated with higher skeletal muscle energetics. Interventions aimed specifically at increasing higher intensity activity might offer potential therapeutic interventions to slow age-related decline in muscle energetics. Our work also emphasizes the importance of taking PA into consideration when evaluating associations related to skeletal muscle energetics.

Role of Cardiorespiratory Fitness and Mitochondrial Oxidative Capacity in Reduced Walk Speed of Older Adults With Diabetes

Cardiorespiratory fitness and mitochondrial oxidative capacity are associated with reduced walking speed in older adults, but their impact on walking speed in older adults with diabetes has not been clearly defined. We examined differences in cardiorespiratory fitness and skeletal muscle mitochondrial oxidative capacity between older adults with and without diabetes, as well as determined their relative contribution to slower walking speed in older adults with diabetes. Participants with diabetes (n = 159) had lower cardiorespiratory fitness and mitochondrial respiration in permeabilized fiber bundles compared with those without diabetes (n = 717), following adjustments for covariates including BMI, chronic comorbid health conditions, and physical activity. Four-meter and 400-m walking speeds were slower in those with diabetes. Mitochondrial oxidative capacity alone or combined with cardiorespiratory fitness mediated ∼20-70% of the difference in walking speed between older adults with and without diabetes. Additional adjustments for BMI and comorbidities further explained the group differences in walking speed. Cardiorespiratory fitness and skeletal muscle mitochondrial oxidative capacity contribute to slower walking speeds in older adults with diabetes.

ARTICLE HIGHLIGHTS

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.

Expression of mitochondrial oxidative stress response genes in muscle is associated with mitochondrial respiration, physical performance, and muscle mass in the Study of Muscle, Mobility, and Aging

Gene expression in skeletal muscle of older individuals may reflect compensatory adaptations in response to oxidative damage that preserve tissue integrity and maintain function. Identifying associations between oxidative stress response gene expression patterns and mitochondrial function, physical performance, and muscle mass in older individuals would further our knowledge of mechanisms related to managing molecular damage that may be targeted to preserve physical resilience. To characterize expression patterns of genes responsible for the oxidative stress response, RNA was extracted and sequenced from skeletal muscle biopsies collected from 575 participants (≥70 years old) from the Study of Muscle, Mobility, and Aging. Expression levels of 21 protein-coding RNAs related to the oxidative stress response were analyzed in relation to six phenotypic measures, including maximal mitochondrial respiration from muscle biopsies (Max OXPHOS), physical performance (VO2 peak, 400-m walking speed, and leg strength), and muscle size (thigh muscle volume and whole-body D3Cr muscle mass). The mRNA level of the oxidative stress response genes most consistently associated across outcomes are preferentially expressed within the mitochondria. Higher expression of mRNAs that encode generally mitochondria located proteins SOD2, TRX2, PRX3, PRX5, and GRX2 were associated with higher levels of mitochondrial respiration and VO2 peak. In addition, greater SOD2, PRX3, and GRX2 expression was associated with higher physical performance and muscle size. Identifying specific mechanisms associated with high functioning across multiple performance and physical domains may lead to targeted antioxidant interventions with greater impacts on mobility and independence.

Signatures of cysteine oxidation on muscle structural and contractile proteins are associated with physical performance and muscle function in older adults: Study of Muscle, Mobility and Aging (SOMMA)

Oxidative stress is considered a contributor to declining muscle function and mobility during aging; however, the underlying molecular mechanisms remain poorly described. We hypothesized that greater levels of cysteine (Cys) oxidation on muscle proteins are associated with decreased measures of mobility. Herein, we applied a novel redox proteomics approach to measure reversible protein Cys oxidation in vastus lateralis muscle biopsies collected from 56 subjects in the Study of Muscle, Mobility and Aging (SOMMA), a community-based cohort study of individuals aged 70 years and older. We tested whether levels of Cys oxidation on key muscle proteins involved in muscle structure and contraction were associated with muscle function (leg power and strength), walking speed, and fitness (VO2 peak on cardiopulmonary exercise testing) using linear regression models adjusted for age, sex, and body weight. Higher oxidation levels of select nebulin Cys sites were associated with lower VO2 peak, while greater oxidation of myomesin-1, myomesin-2, and nebulin Cys sites was associated with slower walking speed. Higher oxidation of Cys sites in key proteins such as myomesin-2, alpha-actinin-2, and skeletal muscle alpha-actin were associated with lower leg power and strength. We also observed an unexpected correlation (R = 0.48) between a higher oxidation level of eight Cys sites in alpha-actinin-3 and stronger leg power. Despite this observation, the results generally support the hypothesis that Cys oxidation of muscle proteins impairs muscle power and strength, walking speed, and cardiopulmonary fitness with aging.

Higher expression of denervation-responsive genes is negatively associated with muscle volume and performance traits in the study of muscle, mobility, and aging (SOMMA)

With aging skeletal muscle fibers undergo repeating cycles of denervation and reinnervation. In approximately the 8th decade of life reinnervation no longer keeps pace, resulting in the accumulation of persistently denervated muscle fibers that in turn cause an acceleration of muscle dysfunction. The significance of denervation in important clinical outcomes with aging is poorly studied. The Study of Muscle, Mobility, and Aging (SOMMA) is a large cohort study with the primary objective to assess how aging muscle biology impacts clinically important traits. Using transcriptomics data from vastus lateralis muscle biopsies in 575 participants we have selected 49 denervation-responsive genes to provide insights to the burden of denervation in SOMMA, to test the hypothesis that greater expression of denervation-responsive genes negatively associates with SOMMA participant traits that included time to walk 400 meters, fitness (VO2peak), maximal mitochondrial respiration, muscle mass and volume, and leg muscle strength and power. Consistent with our hypothesis, increased transcript levels of: a calciumdependent intercellular adhesion glycoprotein (CDH15), acetylcholine receptor subunits (CHRNA1, CHRND, CHRNE), a glycoprotein promoting reinnervation (NCAM1), a transcription factor regulating aspects of muscle organization (RUNX1), and a sodium channel (SCN5A) were each negatively associated with at least 3 of these traits. VO2peak and maximal respiration had the strongest negative associations with 15 and 19 denervation-responsive genes, respectively. In conclusion, the abundance of denervationresponsive gene transcripts is a significant determinant of muscle and mobility outcomes in aging humans, supporting the imperative to identify new treatment strategies to restore innervation in advanced age.

Associations between skeletal muscle energetics and accelerometry-based performance fatigability: Study of Muscle, Mobility and Aging

Performance fatigability is typically experienced as insufficient energy to complete daily physical tasks, particularly with advancing age, often progressing toward dependency. Thus, understanding the etiology of performance fatigability, especially cellular-level biological mechanisms, may help to delay the onset of mobility disability. We hypothesized that skeletal muscle energetics may be important contributors to performance fatigability. Participants in the Study of Muscle, Mobility and Aging completed a usual-paced 400-m walk wearing a wrist-worn ActiGraph GT9X to derive the Pittsburgh Performance Fatigability Index (PPFI, higher scores = more severe fatigability) that quantifies percent decline in individual cadence-versus-time trajectory from their maximal cadence. Complex I&II-supported maximal oxidative phosphorylation (max OXPHOS) and complex I&II-supported electron transfer system (max ETS) were quantified ex vivo using high-resolution respirometry in permeabilized fiber bundles from vastus lateralis muscle biopsies. Maximal adenosine triphosphate production (ATPmax) was assessed in vivo by 31P magnetic resonance spectroscopy. We conducted tobit regressions to examine associations of max OXPHOS, max ETS, and ATPmax with PPFI, adjusting for technician/site, demographic characteristics, and total activity count over 7-day free-living among older adults (N = 795, 70-94 years, 58% women) with complete PPFI scores and ≥1 energetics measure. Median PPFI score was 1.4% [25th-75th percentile: 0%-2.9%]. After full adjustment, each 1 standard deviation lower max OXPHOS, max ETS, and ATPmax were associated with 0.55 (95% CI: 0.26-0.84), 0.39 (95% CI: 0.09-0.70), and 0.54 (95% CI: 0.27-0.81) higher PPFI score, respectively. Our findings suggested that therapeutics targeting muscle energetics may potentially mitigate fatigability and lessen susceptibility to disability among older adults.

The cellular bases of mobility from the Study of Muscle, Mobility and Aging (SOMMA)

Findings from the Study of Muscle, Mobility and Aging (SOMMA) in this issue of Aging Cell show that several biological pathways in skeletal muscle cells play an important role in determining mobility in older adults. These are based on assays in skeletal muscle biopsies obtained from participants, aged 70 years and older in SOMMA tested for association with assessments related to mobility, including muscle mass, strength, power, cardiopulmonary fitness, and 400 m walking speed. The papers show that, using mass spectrometry, oxidative modifications of proteins essential to myocellular function are associated with poorer mobility. Using RNA-seq to quantify gene expression, lower levels of expression of antioxidant enzymes located in mitochondria, autophagy, patterns of expression of genes involved in autophagy, and higher levels of RNA transcripts that increase with denervation were associated with poorer performance on tests of mobility. These results extend previous research from the Baltimore Longitudinal Study of Aging and recent studies from SOMMA showing the importance of mitochondrial energetics in mobility. Together, these findings are painting a picture of how fundamental cellular processes influence the loss of mobility with aging. They may also be a window on aging in other cells, tissues, and systems. The data collected in SOMMA are publicly available and SOMMA welcomes collaborations with scientists who are interested in research about human aging.

The association between chrononutrition behaviors and muscle health among older adults: The study of muscle, mobility and aging

Emerging studies highlight chrononutrition's impact on body composition through circadian clock entrainment, but its effect on older adults' muscle health remains largely overlooked. To determine the associations between chrononutrition behaviors and muscle health in older adults. Dietary data from 828 older adults (76 ± 5 years) recorded food/beverage amounts and their clock time over the past 24 h. Studied chrononutrition behaviors included: (1) The clock time of the first and last food/beverage intake; (2) Eating window (the time elapsed between the first and last intake); and (3) Eating frequency (Number of self-identified eating events logged with changed meal occasion and clock time). Muscle mass (D3-creatine), leg muscle volume (MRI), grip strength (hand-held dynamometer), and leg power (Keiser) were used as outcomes. We used linear regression to assess the relationships between chrononutrition and muscle health, adjusting for age, sex, race, marital status, education, study site, self-reported health, energy, protein, fiber intake, weight, height, and moderate-to-vigorous physical activity. Average eating window was 11 ± 2 h/day; first and last intake times were at 8:22 and 19:22, respectively. After multivariable adjustment, a longer eating window and a later last intake time were associated with greater muscle mass (β ± SE: 0.18 ± 0.09; 0.27 ± 0.11, respectively, p < 0.05). The longer eating window was also marginally associated with higher leg power (p = 0.058). An earlier intake time was associated with higher grip strength (-0.38 ± 0.15; p = 0.012). Chrononutrition behaviors, including longer eating window, later last intake time, and earlier first intake time were associated with better muscle mass and function in older adults.

Associations between regional adipose tissue distribution and skeletal muscle bioenergetics in older men and women

OBJECTIVE

The aim of this study was to examine associations of ectopic adipose tissue (AT) with skeletal muscle (SM) mitochondrial bioenergetics in older adults.

METHODS

Cross-sectional data from 829 adults ≥70 years of age were used. Abdominal, subcutaneous, and visceral AT and thigh muscle fat infiltration (MFI) were quantified by magnetic resonance imaging. SM mitochondrial energetics were characterized in vivo (31P-magnetic resonance spectroscopy; ATPmax) and ex vivo (high-resolution respirometry maximal oxidative phosphorylation [OXPHOS]). ActivPal was used to measure physical activity ([PA]; step count). Linear regression adjusted for covariates was applied, with sequential adjustment for BMI and PA.

RESULTS

Independent of BMI, total abdominal AT (standardized [Std.] β = -0.21; R2 = 0.09) and visceral AT (Std. β = -0.16; R2 = 0.09) were associated with ATPmax (p < 0.01; n = 770) but not following adjustment for PA (p ≥ 0.05; n = 658). Visceral AT (Std. β = -0.16; R2 = 0.25) and thigh MFI (Std. β = -0.11; R2 = 0.24) were associated with carbohydrate-supported maximal OXPHOS independent of BMI and PA (p < 0.05; n = 609). Total abdominal AT (Std. β = -0.19; R2 = 0.24) and visceral AT (Std. β = -0.17; R2 = 0.24) were associated with fatty acid-supported maximal OXPHOS independent of BMI and PA (p < 0.05; n = 447).

CONCLUSIONS

Skeletal MFI and abdominal visceral, but not subcutaneous, AT are inversely associated with SM mitochondrial bioenergetics in older adults independent of BMI. Associations between ectopic AT and in vivo mitochondrial bioenergetics are attenuated by PA.

Autophagy gene expression in skeletal muscle of older individuals is associated with physical performance, muscle volume and mitochondrial function in the study of muscle, mobility and aging (SOMMA)

Autophagy is essential for proteostasis, energetic balance, and cell defense and is a key pathway in aging. Identifying associations between autophagy gene expression patterns in skeletal muscle and physical performance outcomes would further our knowledge of mechanisms related with proteostasis and healthy aging. Muscle biopsies were obtained from participants in the Study of Muscle, Mobility, and Aging (SOMMA). For 575 participants, RNA was sequenced and expression of 281 genes related to autophagy regulation, mitophagy, and mTOR/upstream pathways was determined. Associations between gene expression and outcomes including mitochondrial respiration in muscle fiber bundles (MAX OXPHOS), physical performance (VO2 peak, 400 m walking speed, and leg power), and thigh muscle volume, were determined using negative binomial regression models. For autophagy, key transcriptional regulators including TFE3 and NFKB-related genes (RELA, RELB, and NFKB1) were negatively associated with outcomes. On the contrary, regulators of oxidative metabolism that also promote overall autophagy, mitophagy, and pexophagy (PPARGC1A, PPARA, and EPAS1) were positively associated with multiple outcomes. In line with this, several mitophagy, fusion, and fission-related genes (NIPSNAP2, DNM1L, and OPA1) were also positively associated with outcomes. For mTOR pathway and related genes, expression of WDR59 and WDR24, both subunits of GATOR2 complex (an indirect inhibitor of mTORC1), and PRKAG3, which is a regulatory subunit of AMPK, were negatively correlated with multiple outcomes. Our study identifies autophagy and selective autophagy such as mitophagy gene expression patterns in human skeletal muscle related to physical performance, muscle volume, and mitochondrial function in older persons which may lead to target identification to preserve mobility and independence.

Sex Differences in the Association between Skeletal Muscle Energetics and Perceived Physical Fatigability: The Study of Muscle, Mobility and Aging (SOMMA)

Greater perceived physical fatigability and lower skeletal muscle energetics are predictors of mobility decline. Characterizing associations between muscle energetics and perceived fatigability may provide insight into potential targets to prevent mobility decline. We examined associations of in vivo (maximal ATP production, ATPmax) and ex vivo (maximal carbohydrate supported oxidative phosphorylation [max OXPHOS] and maximal fatty acid supported OXPHOS [max FAO OXPHOS]) measures of mitochondrial energetics with two measures of perceived physical fatigability, Pittsburgh Fatigability Scale (PFS, 0-50, higher=greater) and Rating of Perceived Exertion (RPE Fatigability, 6-20, higher=greater) after a slow treadmill walk. Participants from the Study of Muscle, Mobility and Aging (N=873) were 76.3±5.0 years old, 59.2% women, and 85.3% White. Higher muscle energetics (both in vivo and ex vivo ) were associated with lower perceived physical fatigability, all p<0.03. When stratified by sex, higher ATPmax was associated with lower PFS Physical for men only; higher max OXPHOS and max FAO OXPHOS were associated with lower RPE fatigability for both sexes. Higher skeletal muscle energetics were associated with 40-55% lower odds of being in the most (PFS≥25, RPE Fatigability≥12) vs least (PFS 0-4, RPE Fatigability 6-7) severe fatigability strata, all p<0.03. Being a woman was associated with 2-3 times higher odds of being in the most severe fatigability strata when controlling for ATPmax but not the in vivo measures (p<0.05). Better mitochondrial energetics were linked to lower fatigability and less severe fatigability in older adults. Findings imply that improving skeletal muscle energetics may mitigate perceived physical fatigability and prolong healthy aging.

Energetics and clinical factors for the time required to walk 400 m: The Study of Muscle, Mobility and Aging (SOMMA)

BACKGROUND

Walking slows with aging often leading to mobility disability. Mitochondrial energetics has been found to be associated with gait speed over short distances. Additionally, walking is a complex activity but few clinical factors that may be associated with walk time have been studied.

METHODS

We examined 879 participants ≥70 years and measured the time to walk 400 m. We tested the hypothesis that decreased mitochondrial energetics by respirometry in muscle biopsies and magnetic resonance spectroscopy in the thigh and is associated with longer time to walk 400 m. We also used cardiopulmonary exercise testing to assess the energetic costs of walking: maximum oxygen consumption (VO2peak) and energy cost-capacity (the ratio of VO2, at a slow speed to VO2peak). In addition, we tested the hypothesis that selected clinical factors would also be associated with 400-m walk time.

RESULTS

Lower Max OXPHOS was associated with longer walk time, and the association was explained by the energetic costs of walking, leg power, and weight. Additionally, a multivariate model revealed that longer walk time was also significantly associated with lower VO2peak, greater cost-capacity ratio, weaker leg power, heavier weight, hip and knee stiffness, peripheral neuropathy, greater perceived exertion while walking slowly, greater physical fatigability, less moderate-to-vigorous exercise, less sedentary time, and anemia. Significant associations between age, sex, muscle mass, and peripheral artery disease with 400-m walk time were explained by other clinical and physiologic factors.

CONCLUSIONS

Lower mitochondrial energetics is associated with needing more time to walk 400 m. This supports the value of developing interventions to improve mitochondrial energetics. Additionally, doing more moderate-to-vigorous exercise, increasing leg power, reducing weight, treating hip and knee stiffness, and screening for and treating anemia may reduce the time required to walk 400 m and reduce the risk of mobility disability.

Age Is Associated With Dampened Circadian Patterns of Rest and Activity: The Study of Muscle, Mobility, and Aging (SOMMA)

BACKGROUND

The effects of aging on circadian patterns of behavior are insufficiently described. To address this, we characterized age-specific features of rest-activity rhythms (RAR) in community-dwelling older adults both overall, and in relation, to sociodemographic characteristics.

METHODS

We examined cross-sectional associations between RAR and age, sex, race, education, multimorbidity burden, financial, work, martial, health, and smoking status using assessments of older adults with wrist-worn free-living actigraphy data (N = 820, age = 76.4 years, 58.2% women) participating in the Study of Muscle, Mobility, and Aging (SOMMA). RAR parameters were determined by mapping an extension to the traditional cosine curve to activity data. Functional principal component analysis determined variables accounting for variance.

RESULTS

Age was associated with several metrics of dampened RAR; women had stronger and more robust RAR versus men (all p < .05). Total activity (56%) and time of activity (20%) accounted for most of the RAR variance. Compared to the latest decile of acrophase, those in the earliest decile had higher average amplitude (p < .001). Compared to the latest decile of acrophase, those in the earliest and midrange categories had more total activity (p = .02). Being in a married-like relationship and a more stable financial situation were associated with stronger rhythms; higher education was associated with less rhythm strength (all p < .05).

CONCLUSIONS

Older age was associated with dampened circadian behavior; behaviors were sexually dimorphic. Some sociodemographic characteristics were associated with circadian behavior. We identified a behavioral phenotype characterized by early time of day of peak activity, high rhythmic amplitude, and more total activity.

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.

Skeletal Muscle Energetics Explain the Sex Disparity in Mobility Impairment in the Study of Muscle, Mobility and Aging

The age-related decline in muscle mitochondrial energetics contributes to the loss of mobility in older adults. Women experience a higher prevalence of mobility impairment compared to men, but it is unknown whether sex-specific differences in muscle energetics underlie this disparity. In the Study of Muscle, Mobility and Aging (SOMMA), muscle energetics were characterized using in vivo phosphorus-31 magnetic resonance spectroscopy and high-resolution respirometry of vastus lateralis biopsies in 773 participants (56.4% women, age 70-94 years). A Short Physical Performance Battery (SPPB) score ≤8 was used to define lower-extremity mobility impairment. Muscle mitochondrial energetics were lower in women compared to men (eg, Maximal Complex I&II OXPHOS: Women = 55.06 ± 15.95; Men = 65.80 ± 19.74; p < .001) and in individuals with mobility impairment compared to those without (eg, Maximal Complex I&II OXPHOS in women: SPPB ≥ 9 = 56.59 ± 16.22; SPPB ≤ 8 = 47.37 ± 11.85; p < .001). Muscle energetics were negatively associated with age only in men (eg, Maximal ETS capacity: R = -0.15, p = .02; age/sex interaction, p = .04), resulting in muscle energetics measures that were significantly lower in women than men in the 70-79 age group but not the 80+ age group. Similarly, the odds of mobility impairment were greater in women than men only in the 70-79 age group (70-79 age group, odds ratio [OR]age-adjusted = 1.78, 95% confidence interval [CI] = 1.03, 3.08, p = .038; 80+ age group, ORage-adjusted = 1.05, 95% CI = 0.52, 2.15, p = .89). Accounting for muscle energetics attenuated up to 75% of the greater odds of mobility impairment in women. Women had lower muscle mitochondrial energetics compared to men, which largely explain their greater odds of lower-extremity mobility impairment.

Childhood adverse life events and skeletal muscle mitochondrial function

Social stress experienced in childhood is associated with adverse health later in life. Mitochondrial function has been implicated as a mechanism for how stressful life events "get under the skin" to influence physical well-being. Using data from the Study of Muscle, Mobility, and Aging (n = 879, 59% women), linear models examined whether adverse childhood events (i.e., physical abuse) were associated with two measures of skeletal muscle mitochondrial energetics in older adults: (i) maximal adenosine triphosphate production (ATPmax) and (ii) maximal state 3 respiration (Max OXPHOS). Forty-five percent of the sample reported experiencing one or more adverse childhood events. After adjustment, each additional event was associated with -0.08 SD (95% confidence interval = -0.13, -0.02) lower ATPmax. No association was observed with Max OXPHOS. Adverse childhood events are associated with lower ATP production in later life. Findings indicate that mitochondrial function may be a mechanism for understanding how early social stress influences health in later life.

Usual-paced 400 m long distance corridor walk estimates cardiorespiratory fitness among older adults: The Study of Muscle, Mobility and Aging

BACKGROUND

Cardiopulmonary exercise testing (CPET), the gold-standard method to quantify cardiorespiratory fitness (CRF), is not always feasible due to cost, access, and burden. The usual-paced 400 m long distance corridor walk (LDCW), a measure of mobility among older adults, may provide an alternate method to assess CRF. The purpose of this study was to develop and validate an estimating equation to estimate VO2 peak from average 400 m walking speed (WS) among participants in the Study of Muscle, Mobility and Aging (SOMMA).

METHODS

At baseline, women (58%) and men age 70 years and older enrolled in SOMMA (N = 820, 76.2 ± 4.9 years, 86% Non-Hispanic White) completed a 400 m LDCW (400 m WS = 400 m/completion time in seconds) and symptom-limited maximal CPET (Modified Balke Protocol). VO2 peak (mL/kg/min) was considered the highest 30-second average oxygen consumption during CPET. Other covariates included: age, sex, race, physical activity (7-day wrist-worn accelerometer), physical function (Short Physical Performance Battery, range 0-12), perceived physical fatigability (Pittsburgh Fatigability Scale, range 0-50), and Borg Rating of Perceived Exertion (RPE, range 6-20) at completion of the 400 m LDCW. Stepwise linear regression was used. Internal validation was completed using data-splitting method (70%; 30%).

RESULTS

Mean VO2 peak was 20.2 ± 4.8 mL/kg/min and mean 400 m WS was 1.06 ± 0.2 m/s. Each 0.05 m/s increment in 400 m WS was associated with a 0.40 mL/kg/min higher VO2 peak after covariate adjustment. An estimating equation including 400 m WS, age, sex, race, and RPE was developed. Internal validation showed low overall bias (-0.26) and strong correlation (r = 0.71) between predicted and measured VO2 peak values. Bland-Altman plot and regression analyses indicated predicted VO2 peak was an acceptable alternative, despite mean underestimation of 4.53 mL/kg/min among the highly fit.

CONCLUSIONS

Usual-paced 400 m LDCW strongly correlates with direct measures of CRF during CPET in older adults with lower fitness and can be used to test both fitness and function.

Validation of the Pittsburgh Performance Fatigability Index in the Study of Muscle, Mobility and Aging

BACKGROUND

The Pittsburgh Performance Fatigability Index (PPFI) quantifies the percent decline in cadence using accelerometry during standardized walking tasks. Although PPFI has shown strong correlations with physical performance, the developmental sample was relatively homogenous and small, necessitating further validation.

METHODS

Participants from the Study of Muscle, Mobility and Aging (N = 805, age = 76.4 ± 5.0 years, 58% women, 85% White) wore an ActiGraph GT9X on the nondominant wrist during usual-paced 400 m walk. Tri-axial accelerations were analyzed to compute PPFI (higher score = greater fatigability). To evaluate construct and discriminant validity, Spearman correlations (rs) between PPFI and gait speed, Short Physical Performance Battery (SPPB), chair stand speed, leg peak power, VO2peak, perceived fatigability, and mood were examined. Sex-specific PPFI cut-points that optimally discriminated gait speed using classification and regression tree were then generated. Their discriminate power in relation to aforementioned physical performance were further evaluated.

RESULTS

Median PPFI score was 1.4% (25th-75th percentile range: 0%-21.7%), higher among women than men (p < .001). PPFI score was moderate-to-strongly correlated with gait speed (rs = -0.75), SPPB score (rs = -0.38), chair stand speed (rs = -0.36), leg peak power (rs = -0.34) and VO2peak (rs = -0.40), and less strongly with perceived fatigability (rs = 0.28-0.29), all p < .001. PPFI score was not correlated with mood (|rs| < 0.08). Sex-specific PPFI cut-points (no performance fatigability: PPFI = 0%; mild performance fatigability: 0% < PPFI < 3.5% [women], 0% < PPFI < 5.4% [men]; moderate-to-severe performance fatigability: PPFI ≥ 3.5% [women], PPFI ≥ 5.4% [men]) discriminated physical performance (all p < .001), adjusted for demographics and smoking status.

CONCLUSION

Our work underscores the utility of PPFI as a valid measure to quantify performance fatigability in future longitudinal epidemiologic studies and clinical/pharmaceutical trials.

The association between chrononutrition behaviors and muscle health among older adults: The Study of Muscle, Mobility and Aging (SOMMA)

Background

Emerging studies highlight chrononutrition's impact on body composition through circadian clock entrainment, but its effect on older adults' muscle health remains largely overlooked.

Objective

To determine the associations between chrononutrition behaviors and muscle health in older adults.

Methods

Dietary data from 828 older adults (76±5y) recorded food/beverage amounts and their clock time over the past 24 hours. Studied chrononutrition behaviors included: 1) The clock time of the first and last food/beverage intake; 2) Eating window (the time elapsed between the first and last intake); and 3) Eating frequency (Number of self-identified eating events logged with changed meal occasion and clock time). Muscle mass (D 3 -creatine), leg muscle volume (MRI), grip strength (hand-held dynamometer), and leg power (Keiser) were used as outcomes. We used linear regression to assess the relationships between chrononutrition and muscle health, adjusting for age, sex, race, marital status, education, study site, self-reported health, energy, protein, fiber intake, weight, height, and moderate-to-vigorous physical activity.

Results

Average eating window was 11±2 h/d; first and last intake times were at 8:22 and 19:22, respectively. After multivariable adjustment, a longer eating window and a later last intake time were associated with greater muscle mass (β±SE: 0.18±0.09; 0.27±0.11, respectively, P <0.05). The longer eating window was also marginally associated with higher leg power ( P =0.058). An earlier intake time was associated with higher grip strength (-0.38±0.15; P =0.012).

Conclusions

Chrononutrition behaviors, including longer eating window, later last intake time, and earlier first intake time were associated with better muscle mass and function in older adults.

GRAPHICAL ABSTRACT

Key findings

Chrononutrition behaviors, including longer eating window, later last intake time, and earlier first intake time were associated with better muscle mass and function in older adults.

Age is Associated with Dampened Circadian Patterns of Rest and Activity: The Study of Muscle, Mobility and Aging (SOMMA)

Background

Aging is associated with declines in circadian functions. The effects of aging on circadian patterns of behavior are insufficiently described. We characterized age-specific features of rest-activity rhythms (RAR) in community dwelling older adults, both overall, and in relation, to sociodemographic characteristics.

Methods

We analyzed baseline assessments of older adults with wrist-worn free-living wrist-worn actigraphy data (N=820, Age=76.4 yrs, 58.2% women) participating in the Study of Muscle, Mobility and Aging (SOMMA). We applied an extension to the traditional cosine curve to map RAR to activity data, calculating the parameters: rhythmic strength (amplitude); robustness (pseudo-F statistic); and timing of peak activity (acrophase). We also used function principal component analysis to determine 4 components describing underlying patterns of activity accounting for RAR variance. Linear models were used to examine associations between RAR and sociodemographic variables.

Results

Age was associated with several metrics of dampened RAR; women had stronger and more robust RAR metrics vs. men (all P < 0.05). Total activity (56%) and time of activity (20%) accounted for most the RAR variance. Compared to the latest decile of acrophase, those in the earliest decile had higher average amplitude (P <0.001). Compared to the latest decile of acrophase, those is the earliest and midrange categories had more total activity (P=0.02). RAR was associated with some sociodemographic variables.

Conclusions

Older age was associated with dampened circadian behavior; and behaviors were sexually dimorphic. We identified a behavioral phenotype characterized by early time-of-day of peak activity, high rhythmic amplitude, and more total activity.

Associations between regional adipose tissue distribution and skeletal muscle bioenergetics in older men and women

Objective

Examine the association of ectopic adipose tissue (AT) with skeletal muscle (SM) mitochondrial bioenergetics in older adults.

Methods

Cross-sectional data from 829 older adults ≥70 years was used. Total abdominal, subcutaneous, and visceral AT; and thigh muscle fat infiltration (MFI) was quantified by MRI. SM mitochondrial energetics were characterized using in vivo 31 P-MRS (ATP max ) and ex vivo high-resolution respirometry (maximal oxidative phosphorylation (OXPHOS)). ActivPal was used to measure PA (step count). Linear regression models adjusted for covariates were applied, with sequential adjustment for BMI and PA.

Results

Independent of BMI, total abdominal (standardized (Std.) β=-0.21; R 2 =0.09) and visceral AT (Std. β=-0.16; R 2 =0.09) were associated with ATP max ( p <0.01), but not after further adjustment for PA (p≥0.05). Visceral AT (Std. β=-0.16; R 2 =0.25) and thigh MFI (Std. β=-0.11; R 2 =0.24) were negatively associated with carbohydrate-supported maximal OXPHOS independent of BMI and PA ( p <0.05). Total abdominal AT (Std. β=-0.19; R 2 =0.24) and visceral AT (Std. β=-0.17; R 2 =0.24) were associated with fatty acid-supported maximal OXPHOS independent of BMI and PA (p<0.05).

Conclusions

Skeletal MFI and abdominal visceral, but not subcutaneous AT, are inversely associated with SM mitochondrial bioenergetics in older adults independent of BMI. Associations between ectopic AT and in vivo mitochondrial bioenergetics are attenuated by PA.

Associations between D3Cr muscle mass and MR thigh muscle volume with strength, power, physical performance, fitness, and limitations in older adults in the SOMMA study

Background

Different measures to assess muscle size - magnetic resonance (MR) derived thigh muscle volume and d3-creatine dilution derived muscle mass (D3Cr muscle mass) - may have similar associations with strength, power, physical performance, fitness, and functional limitations in older adults.

Methods

Men (N=345) and women (N=482) aged ≥70 years from the Study of Muscle, Mobility and Aging completed exams including leg extension strength (1-repetition max) and cardiopulmonary exercise testing to assess fitness (VO2peak). Correlations and adjusted regression models stratified by sex were used to assess the association between muscle size measures and study outcomes; we tested for sex interactions.

Results

D3Cr muscle mass and MR thigh muscle volume were correlated (men: r=0.62, women: r=0.51, p<.001). Lower D3Cr muscle mass and lower MR thigh muscle volume were associated with lower strength and lower VO2peak in both men and women; D3Cr muscle mass was more strongly associated with strength in men than in women (p-int<0.05). There were correlations, though less consistent, between muscle size or mass with physical performance and function. Associations between the muscle size measures and the study outcomes occasionally varied by sex, and associations of MR thigh muscle volume were, at times, slightly more strongly associated with the study outcomes than was D3Cr muscle mass.

Conclusions

Less muscle -measured by either D3Cr muscle mass or MR thigh muscle volume - was associated with lower strength and worse performance. Varied associations by sex and assessment method suggest consideration be given to which measurement to use in future studies.

Energetics and Clinical Factors for the Time Required to Walk 400 Meters The Study of Muscle, Mobility and Aging (SOMMA)

Background

Walking slows with aging often leading to mobility disability. Mitochondrial energetics has been found to influence gait speed over short distances. Additionally, walking is a complex activity but few clinical factors that may influence walk time have been studied.

Methods

We examined 879 participants ≥70 years and measured the time to walk 400m. We tested the hypothesis that decreased mitochondrial energetics by respirometry in muscle biopsies and magnetic resonance spectroscopy in the thigh, is associated with longer time to walk 400m. We also used cardiopulmonary exercise testing to assess the energetic costs of walking: maximum oxygen consumption (VO 2 peak) and energy cost-capacity (the ratio of VO2, at a slow speed to VO 2 peak). In addition, we tested the hypothesis that selected clinical factors would also be associated with 400m walk time.

Results

Lower Max OXPHOS was associated with longer walk time and the association was explained by the energetics costs of walking, leg power and weight. Additionally, a multivariate model revealed that longer walk time was also significantly associated with lower VO 2 peak, greater cost-capacity ratio, weaker leg power, heavier weight, hip and knee stiffness, peripheral neuropathy, greater perceived exertion while walking slowly, greater physical fatigability, less moderate-to-vigorous exercise, less sedentary time and anemia. Significant associations between age, sex, muscle mass, and peripheral artery disease with 400m walk time were explained by other clinical and physiologic factors.

Conclusions

Lower mitochondrial energetics is associated with needing more time to walk 400m. This supports the value of developing interventions to improve mitochondrial energetics. Additionally, doing more moderate-to-vigorous exercise, increasing leg power, reducing weight, treating hip and knee stiffness, and screening for and treating anemia may reduce the time required to walk 400m and reduce the risk of mobility disability.

Skeletal muscle energetics explain the sex disparity in mobility impairment in the Study of Muscle, Mobility and Aging (SOMMA)

The age-related decline in muscle mitochondrial energetics contributes to the loss of mobility in older adults. Women experience a higher prevalence of mobility impairment compared to men, but it is unknown whether sex-specific differences in muscle energetics underlie this disparity. In the Study of Muscle, Mobility and Aging (SOMMA), muscle energetics were characterized using in vivo phosphorus-31 magnetic resonance spectroscopy and high-resolution respirometry of vastus lateralis biopsies in 773 participants (56.4% women, age 70-94 years). A Short Physical Performance Battery score ≤ 8 was used to define lower-extremity mobility impairment. Muscle mitochondrial energetics were lower in women compared to men (e.g. Maximal Complex I&II OXPHOS: Women=55.06 +/- 15.95; Men=65.80 +/- 19.74; p<0.001) and in individuals with mobility impairment compared to those without (e.g., Maximal Complex I&II OXPHOS in women: SPPB≥9=56.59 +/- 16.22; SPPB≤8=47.37 +/- 11.85; p<0.001). Muscle energetics were negatively associated with age only in men (e.g., Maximal ETS capacity: R=-0.15, p=0.02; age/sex interaction, p=0.04), resulting in muscle energetics measures that were significantly lower in women than men in the 70-79 age group but not the 80+ age group. Similarly, the odds of mobility impairment were greater in women than men only in the 70-79 age group (70-79 age group, OR age-adjusted =1.78, 95% CI=1.03, 3.08, p=0.038; 80+ age group, OR age-adjusted =1.05, 95% CI=0.52, 2.15, p=0.89). Accounting for muscle energetics attenuated up to 75% of the greater odds of mobility impairment in women. Women had lower muscle mitochondrial energetics compared to men, which largely explain their greater odds of lower-extremity mobility impairment.

The association of skeletal muscle energetics with recurrent falls in older adults within the Study of Muscle, Mobility and Aging (SOMMA)

Background

Falls in the older population are a major public health concern. While many physiological and environmental factors have been associated with fall risk, muscle mitochondrial energetics has not yet been investigated.

Methods

In this analysis, 835 Study of Muscle, Mobility and Aging (SOMMA) participants aged 70-94 were surveyed for recurrent falls (2+) after one year. Skeletal muscle energetics were assessed at baseline in vivo using 31 P Magnetic Resonance Spectroscopy (MRS) (ATPmax) and ex vivo by High Resolution Respirometry (HRR) of permeabilized muscle fibers from the vastus lateralis (MaxOXPHOS).

Results

SOMMA participants who reported recurrent falls (12%) had a slower 400m walk gait speed compared to those with 0-1 falls (1.0 +/-0.2 vs. 1.1 +/-0.2, p<.001) and took a greater number of medication in the 30 days before their baseline visit (5.6 +/-4.4 vs. 4.2 +/-3.4, p<0.05). MaxOXPHOS was significantly lower in those who reported recurrent falls (p=0.008) compared to those with one or fewer falls, but there was no significant difference in ATPmax (p=0.369). Neither muscle energetics measure was significantly associated with total number of falls or injurious falls, but recurrent falls were significantly higher with lower MaxOXPHOS (RR=1.33, 95% CI= 1.02-1.73, p=0.033). However, covariates accounted for the increased risk.

Conclusions

Ex vivo maximal muscle mitochondrial energetics were lower in older adults who experienced recurrent falls, but covariates accounted for its association with recurrent fall risk, suggesting this "hallmark of aging" may not be directly implicated in the complex etiology of falls.

Signatures of Cysteine Oxidation on Muscle Structural and Contractile Proteins Are Associated with Physical Performance and Muscle Function in Older Adults: Study of Muscle, Mobility and Aging (SOMMA)

Oxidative stress is considered a contributor to declining muscle function and mobility during aging; however, the underlying molecular mechanisms remain poorly described. We hypothesized that greater levels of cysteine (Cys) oxidation on muscle proteins are associated with decreased measures of mobility. Herein, we applied a novel redox proteomics approach to measure reversible protein Cys oxidation in vastus lateralis muscle biopsies collected from 56 subjects in the Study of Muscle, Mobility and Aging (SOMMA), a community-based cohort study of individuals aged 70 years and older. We tested whether levels of Cys oxidation on key muscle proteins involved in muscle structure and contraction were associated with muscle function (leg power and strength), walking speed, and fitness (VO2 peak on cardiopulmonary exercise testing) using linear regression models adjusted for age, sex, and body weight. Higher oxidation levels of select nebulin Cys sites were associated with lower VO2 peak, while greater oxidation of myomesin-1, myomesin-2, and nebulin Cys sites was associated with slower walking speed. Higher oxidation of Cys sites in key proteins such as myomesin-2, alpha-actinin-2, and skeletal muscle alpha-actin were associated with lower leg power and strength. We also observed an unexpected correlation (r = 0.48) between a higher oxidation level of 8 Cys sites in alpha-actinin-3 and stronger leg power. Despite this observation, the results generally support the hypothesis that Cys oxidation of muscle proteins impair muscle power and strength, walking speed, and cardiopulmonary fitness with aging.

Childhood adverse life events and skeletal muscle mitochondrial function

Social stress experienced in childhood is associated with adverse health later in life. Mitochondrial function has been implicated as a mechanism for how stressful life events "get under the skin" to influence physical wellbeing. Using data from the Study of Muscle, Mobility and Aging (n=879, 59% women), linear models examined whether adverse childhood events (i.e., physical abuse) were associated with two measures of skeletal muscle mitochondrial energetics in older adults: (1) maximal adenosine triphosphate production (ATP max ) and (2) maximal state 3 respiration (Max OXPHOS). Forty-five percent of the sample reported experiencing 1+ adverse childhood event. After adjustment, each additional event was associated with -0.07 SD (95% CI= - 0.12, -0.01) lower ATP max . No association was observed with Max OXPHOS. Adverse childhood events are associated with lower ATP production in later life. Findings indicate that mitochondrial function may be a mechanism in understanding how early social stress influences health in later life.

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.

Lower Physical Activity Modifies the Association between Perceived Fatigability and Executive Function but not Memory: The Study of Muscle, Mobility and Aging (SOMMA)

OBJECTIVE

Emerging evidence shows that perceived fatigability-the quantification of vulnerability to fatigue in relation to specific intensity and duration of activities-may be associated with cognitive function. We sought to quantify associations with multiple domains of cognitive function and the role of physical activity (PA).

METHODS

SOMMA participants completed the Pittsburgh Fatigability Scale (PFS) Physical and Mental subscales (each range 0-50; higher scores=greater fatigability) and three cognitive function assessments [Digit Symbol Substitution Test (DSST), executive function; Montreal Cognitive Assessment (MoCA), general function; and California Verbal Learning Test (CVLT), memory]. Linear regression quantified associations cross-sectionally between each PFS subscale and cognitive assessment scores adjusting for covariates. Effect modification by volume and intensity of accelerometer-measured PA was assessed.

RESULTS

In 873 participants (59.2% women; age 76.3±5.0; 85% White), mean PFS Physical, Mental, and DSST scores were 15.8±8.7, 7.7±7.8, and 55.4±13.7. After adjustments, for each 4-point higher PFS Physical and 3-point higher PFS Mental, participants had nearly one fewer correct DSST items [β coefficient and 95% confidence interval for PFS Physical: -0.69 (-1.09, - 0.29); PFS Mental: -0.64 (-0.97, -0.30)]. Volume and intensity of PA modified the association of PFS Mental and DSST ( P interactions <0.01). All associations were strongest in those with the lowest volume and intensity of PA. PFS was not associated with MoCA or CVLT.

DISCUSSION

Greater perceived fatigability may be associated with poorer executive function, but not memory. Individuals with greater perceived fatigability, particularly those less active, might benefit from interventions that reduce fatigability and may beneficially influence cognitive function.

Associations of Objective and Self-Reported Physical Activity and Sedentary Behavior with Skeletal Muscle Energetics: The Study of Muscle, Mobility and Aging (SOMMA)

Background

Skeletal muscle energetics decline with age, and physical activity (PA) has been shown to counteract these declines in older adults. Yet, many studies were based on self-reported PA or structured exercise interventions. We examined the associations of objective daily PA and sedentary behavior (SB) with skeletal muscle energetics and also compared with self-reported PA and SB. We also explored the extent to which PA would attenuate the associations of age with muscle energetics.

Methods

Among the Study of Muscle, Mobility and Aging (SOMMA) enrolled older adults, 810 (mean age=76±5, 58% women) had maximal muscle oxidative capacity measured ex vivo via high-resolution respirometry of permeabilized myofibers (maxOXPHOS) and in vivo by 31 Phosphorus magnetic resonance spectroscopy (ATP max ). Objective PA was measured using the wrist-worn ActiGraph GT9X over 7-days to capture sedentary behavior (SB), light, and moderate-to-vigorous PA (MVPA). Self-reported SB, MVPA, and all exercise-related PA were assessed with The Community Healthy Activities Model Program for Seniors questionnaire. Linear regression models with progressive covariate adjustments evaluated the associations between SB, PA and muscle energetics, and the attenuation of the age / muscle energetic association by PA.

Results

Every 30 minutes more objective MVPA was associated with 0.65 pmol/s*mg higher maxOXPHOS and 0.012 mM/sec higher ATP max , after adjustment for age, site/technician and sex. More time spent in objective light+MVPA was significantly associated with higher ATP max , but not maxOXPHOS. In contrast, every 30 minutes spent in objective SB was associated with 0.43 pmol/s*mg lower maxOXPHOS and 0.004 mM/sec lower ATP max . Only associations with ATP max held after further adjusting for socioeconomic status, body mass index, lifestyle factors and multimorbidities. Self-reported MVPA and all exercise-related activities, but not SB, yielded similar associations with maxOXPHOS and ATP max . Lastly, age was only significantly associated with muscle energetics in men. Adjusting for objective time spent in MVPA attenuated the age association with ATP max by nearly 60% in men.

Conclusion

More time spent in daily PA, especially MVPA, were associated with higher muscle energetics. Interventions that increase higher intensity activity might offer potential therapeutic interventions to slow the age-related decline in muscle energetics. Our work also emphasizes the importance of taking PA into consideration when evaluating associations related to skeletal muscle energetics.

Usual-Paced 400m Long Distance Corridor Walk Estimates Cardiorespiratory Fitness among Older Adults: The Study of Muscle, Mobility and Aging (SOMMA)

Background

Cardiopulmonary exercise testing (CPET), the gold-standard method to quantify cardiorespiratory fitness (CRF), is not always feasible due to cost, access, and burden. The usual-paced 400m long-distance corridor walk (LDCW), a measure of mobility among older adults, may provide an alternate method to assess CRF among populations unable to complete maximal intensity testing. The purpose of this study was to develop and validate an estimating equation to estimate VO 2 peak from average 400m walking speed (WS) among participants in the Study of Muscle, Mobility and Aging (SOMMA).

Methods

At baseline, participants (N=820, 76.2±4.9 years, 58% Women, 86% Non-Hispanic White) completed a 400m LDCW (400m WS=400m/completion time in seconds) and symptom-limited maximal CPET (Modified Balke Protocol). VO 2 peak (mL/kg/min) was considered the highest 30-second average oxygen consumption during CPET. Other covariates included: age, sex, race, physical activity (7-day wrist-worn accelerometer), physical function (Short Physical Performance Battery, range 0-12), perceived physical fatigability (Pittsburgh Fatigability Scale, range 0-50), and Borg Rating of Perceived Exertion (RPE, range 6-20) at completion of the 400m LDCW. Stepwise linear regression was used. Internal validation was completed using data-splitting method (70%; 30%).

Results

Mean VO 2 peak was 20.2±4.8 mL/kg/min and mean 400m WS was 1.06±0.2 m/s. Each 0.05 m/s increment in 400m WS was associated with a 0.40 mL/kg/min higher VO 2 peak after adjustment for covariates. An estimating equation including 400m WS, age, sex, race, and RPE was developed. Internal validation showed low overall bias (-0.26) and strong correlation (r = 0.71) between predicted and measured VO 2 peak values. Bland-Altman plot and regression analyses indicated predicted VO 2 peak was an acceptable alternative, despite mean underestimation of 4.53 mL/kg/min among those with CPET VO 2 peak ≥25 mL/kg/min.

Conclusions

Usual-paced 400m LDCW strongly correlates with direct measures of cardiorespiratory fitness during CPET in older adults with lower fitness and can be used to test both fitness and function.

Expression of mitochondrial oxidative stress response genes in muscle is associated with mitochondrial respiration, physical performance, and muscle mass in the Study of Muscle, Mobility and Aging (SOMMA)

Gene expression in skeletal muscle of older individuals may reflect compensatory adaptations in response to oxidative damage that preserve tissue integrity and maintain function. Identifying associations between oxidative stress response gene expression patterns and mitochondrial function, physical performance, and muscle mass in older individuals would further our knowledge of mechanisms related to managing molecular damage that may be targeted to preserve physical resilience. To characterize expression patterns of genes responsible for the oxidative stress response, RNA was extracted and sequenced from skeletal muscle biopsies collected from 575 participants (≥70 years old) from the Study of Muscle, Mobility and Aging. Expression levels of twenty-one protein coding RNAs related to the oxidative stress response were analyzed in relation to six phenotypic measures, including: maximal mitochondrial respiration from muscle biopsies (Max OXPHOS), physical performance (VO2 peak, 400m walking speed, and leg strength), and muscle size (thigh muscle volume and whole-body D3Cr muscle mass). The mRNA level of the oxidative stress response genes most consistently associated across outcomes are preferentially expressed within the mitochondria. Higher expression of mRNAs that encode generally mitochondria located proteins SOD2, TRX2, PRX3, PRX5, and GRX2 were associated with higher levels of mitochondrial respiration and VO2 peak. In addition, greater SOD2, PRX3, and GRX2 expression was associated with higher physical performance and muscle size. Identifying specific mechanisms associated with high functioning across multiple performance and physical domains may lead to targeted antioxidant interventions with greater impacts on mobility and independence.

Role of Cardiorespiratory Fitness and Mitochondrial Energetics in Reduced Walk Speed of Older Adults with Diabetes in the Study of Muscle, Mobility and Aging (SOMMA)

Rationale

Cardiorespiratory fitness and mitochondrial energetics are associated with reduced walking speed in older adults. The impact of cardiorespiratory fitness and mitochondrial energetics on walking speed in older adults with diabetes has not been clearly defined.

Objective

To examine differences in cardiorespiratory fitness and skeletal muscle mitochondrial energetics between older adults with and without diabetes. We also assessed the contribution of cardiorespiratory fitness and skeletal muscle mitochondrial energetics to slower walking speed in older adults with diabetes.

Findings

Participants with diabetes had lower cardiorespiratory fitness and mitochondrial energetics when compared to those without diabetes, following adjustments for covariates including BMI, chronic comorbid health conditions, and physical activity. 4-m and 400-m walking speeds were slower in those with diabetes. Mitochondrial oxidative capacity alone or combined with cardiorespiratory fitness mediated ∼20-70% of the difference in walk speed between older adults with and without diabetes. Further adjustments of BMI and co-morbidities further explained the group differences in walk speed.

Conclusions

Skeletal muscle mitochondrial energetics and cardiorespiratory fitness contribute to slower walking speeds in older adults with diabetes. Cardiorespiratory fitness and mitochondrial energetics may be therapeutic targets to maintain or improve mobility in older adults with diabetes.

ARTICLE HIGHLIGHTS

Why did we undertake this study? To determine if mitochondrial energetics and cardiorespiratory fitness contribute to slower walking speed in older adults with diabetes. What is the specific question(s) we wanted to answer? Are mitochondrial energetics and cardiorespiratory fitness in older adults with diabetes lower than those without diabetes? How does mitochondrial energetics and cardiorespiratory fitness impact walking speed in older adults with diabetes? What did we find? Mitochondrial energetics and cardiorespiratory fitness were lower in older adults with diabetes compared to those without diabetes, and energetics, and cardiorespiratory fitness, contributed to slower walking speed in those with diabetes. What are the implications of our findings? Cardiorespiratory fitness and mitochondrial energetics may be key therapeutic targets to maintain or improve mobility in older adults with diabetes.