Biology subjects

Altheyab, A.

Publications and source records attributed to Altheyab, A..

3 recordsLinked to original sources

bioRxiv2025

Task Complexity and Limb Dominance Modulate the Effects of Ageing on Neuromuscular Function

BackgroundNeuromuscular function is critical for independence in ageing, yet asymmetries between dominant and non-dominant limbs, arising from central or peripheral mechanisms, are not well understood. This study examined age- and limb-related differences and motor unit (MU) firing behaviour of the vastus lateralis under tasks of varying difficulty. MethodsTwenty-one young (22 {+/-} 4 years; 15M, 6F) and seventeen older adults (74 {+/-} 5 years; 12M, 5F) performed constant and variable force unilateral isometric knee extensions. In both limbs, high-density surface electromyography signals were decomposed into MU spike trains. Force control and MU firing properties were analysed using multilevel mixed-effects regression models. ResultsOlder adults showed reduced maximal muscle strength (p<0.001) and increased force tracking error (p=0.008), MU firing rate (MUFR) was significantly lower in older adults during constant contractions (p = 0.001) and trended toward lower during variable contractions (p=0.061). MUFR variability showed a significant Leg x AgeGroup interaction (p<0.001); older adults had greater variability in non-dominant legs, while younger adults showed the opposite. With variable force contractions in both age groups, MUFR was higher during ascending segments with greater variability during descending segments. ConclusionNeuromuscular ageing involves asymmetric adaptations rather than a uniform decline, with leg dominance effects become more pronounced under variable force modulation. Task difficulty amplifies these asymmetries, underscoring the need to consider limb-specific neural control in age-related motor assessments.

physiology↗

bioRxiv2025

Bilateral neuromuscular adaptation to acute unilateral resistance exercise in healthy older adults

IntroductionResistance exercise (RE) enhances functionality in older adults and has proven effective as a means of cross-education in scenarios of unilateral disuse. However, the extent to which older adults demonstrate cross-limb transfer at the motor unit (MU) level following a single bout of unilateral RE is unclear. MethodsThirteen healthy older adults (74.9 {+/-} 4.8 years; 5 females) underwent bilateral neuromuscular assessments pre- and post- a single bout of unilateral RE consisting of 3-4 sets of 8-12 repetitions of leg extension of the dominant (exercise) leg, at 75% of 1 repetition maximum, performed to failure. Maximum voluntary contraction (MVC) and force steadiness (FS) were measured. Central and peripheral features of individual MU were recorded using high-density surface electromyography and intramuscular electromyography (HDs/iEMG), during contractions normalised to 25% MVC. ResultsFollowing unilateral RE, MVC reduced in exercise (-14.8%, p < 0.001) and control (-6.9%, p = 0.003) legs, with reduced FS performance in the exercise leg compared to the control (p = 0.002). MU firing rate increased during contractions normalised to 25% baseline MVC in the exercised leg (p < 0.05), with no adaptation in the control leg (p > 0.05). All iEMG recorded measures of MU potentials remained unchanged in both legs (all p > 0.05). ConclusionAcute unilateral RE leads to bilateral MVC reduction in older males and females, demonstrating the cross-limb transfer effect. However, adaptation of MU features was only apparent in the exercised limb, and mechanisms underlying the force decline in the non- exercised limb remain uncertain.

physiology↗

bioRxiv2023

Sex disparities in age-related neuromuscular decline: unveiling female susceptibility from early to late elderly

BackgroundFemales typically have a longer lifespan than males which is not matched by an improved healthspan, with older females having higher rates of frailty, characteristic of a sex specific degradation of the neuromuscular system. Several motor unit (MU) characteristics show sex-specific behaviour during mid-level contractions in healthy younger people, highlighting a potential influence of hormonal differences that may be augmented in older age. The purpose of this study was to investigate sex differences in physical performance and MU features of the aged human vastus lateralis (VL) from early to late elderly. MethodsThis study included 21 healthy older males (mean {+/-} SD, range: 67.2 {+/-} 7.6, 56 - 81 yrs) and 17 healthy older females (69.5 {+/-} 5.2, 60 - 78 yrs). Intramuscular electromyography data were collected from VL during standardised submaximal sustained contractions. Muscle size and physical performance characteristics were also measured. Multiple mixed-effects linear regression models with age considered were conducted and statistical significance was accepted when p<0.05. ResultsWhen compared to males, early to late elderly females had smaller cross-sectional area of VL (p<0.001), lower knee extensor torque (p<0.001) and poorer force steadiness (p=0.036), as well as higher MU firing rate (FR) (p=0.025) and greater MU FR variability (p=0.031). With progression from early to late elderly, both sexes showed decreased functional capacity at a similar rate. ConclusionFunctional deterioration occurs to a similar extent in both sexes from early to late elderly. However, throughout the majority of the elderly period males demonstrate a greater muscle size, strength, and functional performance. Older females have greater MUFR variability and worse force steadiness than older males. These findings help to address the lack of MU data in older females, and suggest earlier interventions are needed in older females to prevent functional deterioration and reduce the health-sex paradox within ageing humans.

physiology↗