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Females typically live longer than males but, paradoxically, spend a greater number of later years in poorer health. The neuromuscular system is a critical component of the progression to frailty, and motor unit (MU) characteristics differ by sex in healthy young individuals and may adapt to ageing in a sex‐specific manner due to divergent hormonal profiles. The purpose of this study was to investigate sex differences in vastus lateralis (VL) MU structure and function in early to late elderly humans. Intramuscular electromyography signals from 50 healthy older adults (M/F: 26/24) were collected from VL during standardized submaximal contractions and decomposed to quantify MU characteristics. Muscle size and neuromuscular performance were also measured. Females had higher MU firing rate (FR) than males (P = 0.025), with no difference in MU structure or neuromuscular junction transmission (NMJ) instability. All MU characteristics increased from low‐ to mid‐level contractions (P < 0.05) without sex × level interactions. Females had smaller cross‐sectional area of VL, lower strength and poorer force steadiness (P < 0.05). From early to late elderly, both sexes showed decreased neuromuscular function (P < 0.05) without sex‐specific patterns. Higher VL MUFRs at normalized contraction levels previously observed in young are also apparent in old individuals, with no sex‐based difference of estimates of MU structure or NMJ transmission instability. From early to late elderly, the deterioration of neuromuscular function and MU characteristics did not differ between sexes, yet function was consistently greater in males. These parallel trajectories underscore the lower initial level for older females and may offer insights into identifying critical intervention periods. Key points: Females generally exhibit an extended lifespan when compared to males, yet this is accompanied by a poorer healthspan and higher rates of frailty.In healthy young people, motor unit firing rate (MUFR) at normalized contraction intensities is widely reported to be higher in females than in age‐matched males.Here we show in 50 people that older females have higher MUFR than older males with little difference in other MU parameters. The trajectory of decline from early to late elderly does not differ between sexes, yet function is consistently lower in females.These findings highlight distinguishable sex disparities in some MU characteristics and neuromuscular function, and suggest early interventions are needed for females to prevent functional deterioration to reduce the ageing health–sex paradox. [ABSTRACT FROM AUTHOR]

Impairments in myofibrillar protein synthesis (MyoPS) during bed rest accelerate skeletal muscle loss in older adults, increasing the risk of adverse secondary health outcomes. We investigated the effect of prior resistance exercise (RE) on MyoPS and muscle morphology during a disuse event in 10 healthy older men (65–80 years). Participants completed a single bout of unilateral leg RE the evening prior to 5 days of in‐patient bed‐rest. Quadriceps cross‐sectional area (CSA) was determined prior to and following bed‐rest. Serial muscle biopsies and dual stable isotope tracers were used to determine rates of integrated MyoPS (iMyoPS) over a 7 day habitual 'free‐living' phase and the bed‐rest phase, and rates of acute postabsorptive and postprandial MyoPS (aMyoPS) at the end of bed rest. Quadriceps CSA at 40%, 60% and 80% of muscle length significantly decreased in exercised (EX) and non‐exercised control (CTL) legs with bed‐rest. The decline in quadriceps CSA at 40% and 60% of muscle length was attenuated in EX compared with CTL. During bed‐rest, iMyoPS rates decreased from habitual values in CTL, but not EX, and were significantly different between legs. Postprandial aMyoPS rates increased above postabsorptive values in EX only. The change in iMyoPS over bed‐rest correlated with the change in quadriceps CSA in CTL, but not EX. A single bout of RE attenuated the decline in iMyoPS rates and quadriceps atrophy with 5 days of bed‐rest in older men. Further work is required to understand the functional and clinical implications of prior RE in older patient populations. Key points: Age‐related skeletal muscle deterioration, linked to numerous adverse health outcomes, is driven by impairments in muscle protein synthesis that are accelerated during periods of disuse.Resistance exercise can stimulate muscle protein synthesis over several days of recovery and therefore could counteract impairments in this process that occur in the early phase of disuse.In the present study, we demonstrate that the decline in myofibrillar protein synthesis and muscle atrophy over 5 days of bed‐rest in older men was attenuated by a single bout of unilateral resistance exercise performed the evening prior to bed‐rest.These findings suggest that concise resistance exercise intervention holds the potential to support muscle mass retention in older individuals during short‐term disuse, with implications for delaying sarcopenia progression in ageing populations. [ABSTRACT FROM AUTHOR]

Background/Objectives: The acute phase of stroke is marked by inflammation and mobility changes that can compromise nutritional status. This study was a randomized, double-blind, placebo-controlled trial evaluating the effectiveness of creatine supplementation for older people during seven days of hospitalization for stroke compared to usual care. Method: The primary outcome measures were changes in functional capacity, strength, muscle mass, and muscle degradation. The secondary outcomes were changes in serum biomarkers related to inflammation, fibrosis, anabolism, and muscle synthesis. In addition, a follow-up 90 days after the stroke verified functional capacity, strength, quality of life, and mortality. Following admission for an acute stroke, participants received either creatine (10 g) or a visually identical placebo (10 g) orally twice daily. Both groups received supplementation with protein to achieve the goal of 1.5 g of protein/kg of body weight/day and underwent daily mobility training during seven days of hospitalization. Results: Thirty older people were included in two similar groups concerning baseline attributes (15—treatment/15—placebo). Conclusions: Creatine supplementation did not influence functional capacity, strength, or muscle mass during the first 7 days or outcomes 90 days after stroke. There were no serious adverse events associated with creatine supplementation. However, it decreased progranulin levels, raising a new possibility of creatine action. This finding needs further exploration to understand the biological significance of creatine–progranulin interaction. [ABSTRACT FROM AUTHOR]

To examine the effect of the NAD+ precursor, nicotinic acid (NA), for improving skeletal muscle status in sedentary older people. In a double-blind, randomised, placebo-controlled design, 18 sedentary yet otherwise healthy older (65–75 y) males were assigned to 2-weeks of NA (acipimox; 250 mg × 3 daily, n=8) or placebo (PLA, n=10) supplementation. At baseline, and after week 1 and week 2 of supplementation, a battery of functional, metabolic, and molecular readouts were measured. Resting and submaximal respiratory exchange ratio was lower (p<0.05) after 2 weeks in the NA group only, but maximal aerobic and anaerobic function and glucose handling were unchanged (p>0.05). Bayesian statistical modelling identified that leak, maximal coupled and maximal uncoupled mitochondrial respiratory states, increased over the 2-week supplemental period in the NA group (probability for a positive change (pd) 85.2, 90.8 and 95.9 %, respectively) but not in PLA. Citrate synthase and protein content of complex II (SDHB) and V (ATP5A) electron transport chain (ETC) components increased over the 2-week period in the NA group only (pd 95.1, 74.5 and 82.3 %, respectively). Mitochondrial and myofibrillar protein synthetic rates remained unchanged in both groups. NA intake altered the muscle transcriptome by increasing the expression of gene pathways related to cell adhesion/cytoskeleton organisation and inflammation/immunity and decreasing pathway expression of ETC and aerobic respiration processes. NAD+-specific pathways (e.g., de novo NAD+ biosynthetic processes) and genes (e.g., NADSYN1) were uniquely regulated by NA. NA might be an effective strategy for improving ageing muscle mitochondrial health. [ABSTRACT FROM AUTHOR]