Aging, resistance training, and motor unit discharge behavior

Neuromuscular characteristics of front and back legs in junior fencers

In elite fencers, muscle strength and muscle mass of the front leg (FL) are greater than those of the back leg (BL) due to characteristic physiological and biomechanical demands placed on each leg during fencing. However, the development of laterality in their neural and muscular components is not well-understood. The present study investigated neuromuscular characteristics of FL and BL in junior fencers. Nineteen junior fencers performed neuromuscular performance tests for FL and BL, separately. There were no significant differences in the isometric knee extension strength (MVC), unilateral vertical jump (UVJ), vastus lateralis muscle thickness (MT), or motor unit firing rate of the vastus lateralis muscle (MUFR) between FL and BL (p > 0.05). In subgroup analyses, a significantly greater MUFR in FL than BL was noted only in fencers with > 3 years of fencing experience, and significantly greater UVJ in FL than BL was observed solely in fencers with < 3 years of fencing experience (p < 0.05). Strong positive correlations between FL and BL were identified in MVC, MT, and MUFR in fencers with > 3 years of fencing experience, but not in those with < 3 years of experience. These findings suggest that in junior fencers, laterality in neuromuscular performance has not manifested, whereas longer fencing experience induces fencing-dependent laterality in neural components, and laterality in dynamic muscle strength is decreased with fencing experience.

The Effects of High-Speed Resistance Training on Health Outcomes in Independent Older Adults: A Systematic Review and Meta-Analysis

Human ageing involves several physiological impairments—in particular, a decrease in sensorimotor function and changes in the nervous system reduce muscle strength, power, balance, and functional capacity performance. Preventive strategies are essential to ensure the quality of life of the elderly. High-speed resistance training (HSRT) may be an effective approach to muscle power development in this population, with significant short-term effects on neural adaptations and muscle power production. Therefore, the present study intends to analyze and systematize the studies focused on HSRT interventions and their effects on health outcomes in independent older adults. Four electronic databases (PubMed, Web of Science, EBSCO, and Scielo) were used for the purposes of searching randomized controlled trials that measured at least one key outcome measure focusing on velocity-based training and health outcomes in older adults on 7 March 2022 and identified 1950 studies. At the end of the process, fourteen studies were included in this systematic review and ten studies were included in the quantitative analysis. The main results showed that HSRT interventions would improve health measures, mostly cognitive function (large effects, p = 0.001, SMD = 0.94), neuromuscular function (moderate effects, p = 0.003, SMD = 0.70), and physical function (moderate effects, p = 0.04, SMD = 0.55 and p = 0.009, SMD = −0.59). Additionally, the results suggested that interventions with ten weeks or more, performed three times a week, provide significant improvements in neuromuscular function. In this sense, HSRT is effective for improving overall health outcomes in older adults. Future studies should include proper follow-ups (e.g., minimum six months) to assess the durability of HSRT intervention effects on all health-related variables.

Effect of repeated eccentric exercise on muscle damage markers and motor unit control strategies in arm and hand muscle

To examine the contralateral repeated bout effect (CL-RBE) on muscle damage markers and motor unit (MU) control strategies, seventeen healthy adults performed two bouts of 60 eccentric contractions with elbow flexor (EF group; n ​= ​9) or index finger abductor (IA group; n ​= ​8) muscles, separated by 1 week. All participants randomly performed eccentric exercise on either the right or left arm or hand muscles, and muscle damage markers and submaximal trapezoid contraction tests were conducted pre, post, 1- and 2-day post eccentric protocol. One week after the first bout, the same exercise protocol and measurements were performed on the contralateral muscles. Surface electromyographic (EMG) signals were collected from biceps brachii (BB) or first dorsal interosseous (FDI) during maximal and submaximal tests. The linear regression analyses were used to examine MU recruitment threshold versus mean firing rate and recruitment threshold versus derecruitment threshold relationships. EMG amplitude from BB (bout 1 vs. bout 2 ​= ​65.71% ​± ​22.92% vs. 43.05% ​± ​18.97%, p ​= ​0.015, d ​= ​1.077) and the y-intercept (group merged) from the MU recruitment threshold versus derecruitment threshold relationship (bout 1 vs. bout 2 ​= ​−7.10 ​± ​14.20 vs. 0.73 ​± ​16.24, p ​= ​0.029, d ​= ​0.513) at 50% MVIC were significantly different between two bouts. However, other muscle damage markers did not show any CL-RBE in both muscle groups. Therefore, despite changes in muscle excitation and MU firing behavior, our results do not support the existence of CL-RBE on BB and FDI muscles.

Long-Term Benefits of Tailored Exercise in Severe Sarcoidosis: A Case Report

BACKGROUND

We studied the effects of a supervised, structured exercise program in a severe sarcoidosis patient.

METHODS

After being clinically stable for two years, a 52-year-old woman (stage IV, American Thoracic Society) who originally had irreversible lung fibrosis, pulmonary arterial hypertension (PAH), mild mitral insufficiency, and atrial dilatation, and was candidate for lung transplant, performed a combined high-intensity interval, high load resistance, and inspiratory muscle training for 4.5 years, and was tested (cardiopulmonary exercise testing and dual X-ray absorptiometry) every six months.

RESULTS

Cardiorespiratory fitness (CRF) and maximal pulmonary ventilation increased by 44% and 60%, respectively. Ventilatory efficiency also improved (decrease in the ventilatory equivalent for oxygen by 32% and 14% at the ventilatory threshold and respiratory compensation point, respectively). She improved New York Heart Association (NYHA) class (from III to II), and cardiac alterations as well as PAH reversed so that she was not in need of lung transplantation anymore. Likewise, she suffered no more episodes of hemoptysis. Bone health was overall maintained despite the post-menopausal status and the corticoid treatment.

CONCLUSIONS

A long-term combined exercise intervention safely contributed-at least partly-to improve CRF and NYHA class in a patient with severe sarcoidosis, suggesting a potential coadjuvant effect to attenuate clinical manifestations.

Comparison between Two Inspiratory Muscle Training Protocols, Low Loads versus High Loads, in Institutionalized Elderly Women: A Double-Blind Randomized Controlled Trial

BACKGROUND

Aging results in a decline in the function of the respiratory muscles. Inspiratory muscle training is presented as a possible solution to attenuate the loss of respiratory function in the elderly. The objective of the study was to evaluate and compare the efficacy of 2 protocols with inspiratory muscle training (IMT), low loads and high loads, to improve respiratory strength, functional capacity and dyspnea in institutionalized elderly women, over 65 years.

METHODS

The study was a controlled, randomized, double-blind trial and with allocation concealment performed on 26 institutionalized elderly women distributed in 2 groups, the high-intensity group (HIG) and low-intensity group (LIG). Over an 8-week period an IMT protocol was followed 5 days/week, 15 min/day. The HIG trained with a load of 40% of the maximum inspiratory pressure (MIP) and the LIG with 20%. MIP, maximum expiratory pressure (MEP), functional capacity and dyspnea were evaluated.

RESULTS

After training, in the HIG MIP, MEP and functional capacity increased 52, 16 and 7%, respectively (p = 0.000, p = 0.001, p = 0.001) and in the LIG 30, 18 and 9%, respectively (p = 0.002, p = 0.014, p = 0.001). The improvement in MIP was significantly higher in the HIG than in the LIG (p = 0.042).

CONCLUSION

IMT with low and high loads improves respiratory muscle strength and functional capacity in institutionalized elderly women. In addition, high loads were significantly more effective to improve MIP.

Preserving Mobility in Older Adults with Physical Frailty and Sarcopenia: Opportunities, Challenges, and Recommendations for Physical Activity Interventions

One of the most widely conserved hallmarks of aging is a decline in functional capabilities. Mobility loss is particularly burdensome due to its association with negative health outcomes, loss of independence and disability, and the heavy impact on quality of life. Recently, a new condition, physical frailty and sarcopenia, has been proposed to define a critical stage in the disabling cascade. Physical frailty and sarcopenia are characterized by weakness, slowness, and reduced muscle mass, yet with preserved ability to move independently. One of the strategies that have shown some benefits in combatting mobility loss and its consequences for older adults is physical activity. Here, we describe the opportunities and challenges for the development of physical activity interventions in people with physical frailty and sarcopenia. The aim of this article is to review age-related physio(patho)logical changes that impact mobility in old age and to provide recommendations and procedures in accordance with the available literature.

Human motor unit characteristics of the superior trapezius muscle with age-related comparisons

Current understanding of human motor unit (MU) control and aging is mostly derived from hand and limb muscles that have spinal motor neuron innervations. The aim here was to characterize and test whether a muscle with a shared innervation supply from brainstem and spinal MU populations would demonstrate similar age-related adaptations as those reported for other muscles. In humans, the superior trapezius (ST) muscle acts to elevate and stabilize the scapula and has primary efferent supply from the spinal accessory nerve (cranial nerve XI) located in the brainstem. We compared electrophysiological properties obtained from intramuscular and surface recordings between 10 young (22-33 yr) and 10 old (77-88 yr) men at a range of voluntary isometric contraction intensities (from 15 to 100% of maximal efforts). The old group was 41% weaker with 43% lower MU discharge frequencies compared with the young (47.2 ± 9.6 Hz young and 26.7 ± 5.8 Hz old, P < 0.05) during maximal efforts. There was no difference in MU number estimation between age groups (228 ± 105 young and 209 ± 89 old, P = 0.33). Furthermore, there were no differences in needle detected near fiber (NF) stability parameters of jitter or jiggle. The old group had lower amplitude and smaller area of the stimulated compound muscle action potential and smaller NF MU potential area with higher NF counts. Thus, despite age-related ST weakness and lower MU discharge rates, there was minimal evidence of MU loss or compensatory reinnervation.NEW & NOTEWORTHY The human superior trapezius (ST) has shared spinal and brainstem motor neuron innervation providing a unique model to explore the impact of aging on motor unit (MU) properties. Although the ST showed higher MU discharge rates compared with most spinally innervated muscles, voluntary strength and mean MU rates were lower in old compared with young at all contraction intensities. There was no age-related difference in MU number estimates with minimal electrophysiological evidence of collateral reinnervation.

Muscle Mass, Quality, and Composition Changes During Atrophy and Sarcopenia

Skeletal muscle mass (SMM) and muscle strengh reach their peak in 20s to 40s of age in human life and then decrease with advancing age. The decrease rate of muscle strength or power was twice to four times as large as that of the SMM. Thus, the normalized muscle force (muscle strength divided by SMM) also decreases in aging. It depends on the number of factors in skeletal muscle tissues and neuromuscular system. In human study, SMM cannot be measured directly without dissection so that all of the methodologies are indirect methods to assess SMM, even computing tomography or magnetic resonance imaging. Dual-energy X-ray absorptiometry, ultrasonography, anthropometry, and bioelectrical impedance analysis (BIA) are used as secondary indirect methods to estimate SMM. Recent researches show muscle composition changes in aging, and in particular, the ratio of muscle cell mass (MCM) against SMM decrease and relative expansion of extracellular water (ECW) and extracellular space is observed with advancing age and/or decrease of physical function. The intracellular water (ICW) and ECW estimated by segmental bioelectrical impedance spectroscopy or multifrequency BIA are good biomarkers of the ratio of MCM against SMM in limbs. The BIS and other state-of-the-art technology for assessment of muscle mass, quality, and composition are useful to fully understand the muscle atrophy in a living organism.

The Extracellular to Intracellular Water Ratio in Upper Legs is Negatively Associated With Skeletal Muscle Strength and Gait Speed in Older People

Skeletal muscles contain a large volume of water that is classified into intracellular (ICW) and extracellular (ECW) water fractions. Nuclear magnetic resonance-based biomarkers suggest that increased water T2 heterogeneities, as well as elevated water T2 relaxation in the quadriceps occurs in the elderly when compared with young adults. However, nuclear magnetic resonance is difficult to apply to a large-scale study or a clinical setting for sarcopenia and frailty screening. Segmental bioelectrical impedance spectroscopy is a unique tool used to assess the segmental ratio of ECW/ICW in the limbs. We evaluated 405 community-living people aged between 65 and 90 years. ECW and ICW in the upper legs were assessed by segmental bioelectrical impedance spectroscopy. Isometric knee extension strength, gait speed, and skeletal muscle mass were measured. Thigh ECW/ICW was negatively correlated with knee extension strength and gait speed (r = -.617 and -.431, respectively, p < .001) and increased with age (p < .001). Thigh ECW/ICW was a significant predictor of knee extension strength and gait speed independent of age, sex, body mass index, and skeletal muscle mass. Relative expansion of ECW against ICW in the thigh muscles is a factor in decreased muscle quality and a biomarker of muscle aging.

Sarcopenia: Neurological Point of View

Sarcopenia is an age-related geriatric syndrome which is characterized by the gradual loss of muscle mass, muscle strength, and muscle quality. There are a lot of neurologic insults on sarcopenia at various levels from the brain to the neuromuscular junctions (NMJs) to generate a volitional task. Dopaminergic downregulation, inadequate motor programming and motor coordination impairment lead to decline of supraspinal drive. Motor unit reorganization and inflammatory changes in motor neuron decrease conduction velocity and amplitude of compound muscle action potential. Furthermore, NMJ remodeling and age related neurophysiological alterations may contribute to neuromuscular impairment. Sarcopenia is an age-associated, lifelong process which links to multiple etiological factors. Although not all the causes are completely understood, we suggest that compromised nervous system function may be one of the important contributors to the sarcopenia.

Age-Related Changes in Morphology and Function of Scapular Muscles in Asymptomatic People

BACKGROUND

Aging is a contributing factor to rotator cuff tears. Dysfunction of the scapular muscles can be a potential cause of rotator cuff tears. Although aging can contribute to dysfunction of the scapular muscles and subsequently result in rotator cuff tears, the effects of aging on scapular muscles are unclear.

OBJECTIVE

To determine changes in sizes and electromyographic activities of the scapular muscles with age in asymptomatic subjects.

DESIGN

Cross-sectional study.

PATIENTS

Fifty-four asymptomatic subjects without shoulder pain and dysfunction (18 male and 36 female) were recruited for this study. Subjects consisted of 19 people aged 20-39 years (young adult group, 27.2 ± 5.2 years), 17 people aged 40-59 years (middle age group, 49.9 ± 6.6 years), and 18 people aged 60-79 years (elderly group, 68.0 ± 7.1 years).

METHODS

Using ultrasonography, we measured the muscle thickness of the trapezius (upper and lower portions), serratus anterior, and middle deltoid muscles during rest with the subject in a sitting position. Activities of the same muscles were measured with surface electromyography during shoulder elevation in the scapular plane up to 120°. The electromyographic data were analyzed at ranges 0°-30°, 30°-60°, and 60°-90°. Analysis of variance and Bonferroni multiple comparisons were used for statistical analysis.

RESULTS

Muscle thickness of the lower trapezius in the elderly group was decreased significantly compared with that in the young adult group (95% confidence interval -0.40, 2.24; P < .001) and middle age group (95% confidence interval -0.34, 1.89; P = .012). There were no significant differences in muscle activity and activity ratio between groups.

CONCLUSION

In scapular muscles, muscle thickness of the lower trapezius significantly decreased with aging, although there were no decreases in muscle thicknesses of the other muscles between different age groups. For the functional change, aging may not affect the scapular muscle activities and balance of the activities between the deltoid and scapular muscles.

LEVEL OF EVIDENCE

IV.

Gender differences in the association between grip strength and mortality in older adults: results from the KORA-age study

Background

Reduced muscular strength in the old age is strongly related to activity impairment and mortality. However, studies evaluating the gender-specific association between muscularity and mortality among older adults are lacking. Thus, the objective of the present study was to examine gender differences in the association between muscular strength and mortality in a prospective population-based cohort study.

Methods

Data used in this study derived from the Cooperative Health Research in the Region of Augsburg (KORA)-Age Study. The present analysis includes 1,066 individuals (mean age 76 ± 11 SD years) followed up over 3 years. Handgrip strength was measured using the Jamar Dynamometer. A Cox proportional hazard model was used to determine adjusted hazard ratios of mortality with 95% confidence intervals (95% CI) for handgrip strength. Potential confounders (i.e. age, nutritional status, number of prescribed drugs, diseases and level of physical activity) were pre-selected according to evidence-based information.

Results

During the follow-up period, 56 men (11%) and 39 women (7%) died. Age-adjusted mortality rates per 1,000 person years (95% CI) were 77 (59–106), 24 (13–41) and 14 (7–30) for men and 57 (39–81), 14 (7–27) and 1 (0–19) for women for the first, second and third sex-specific tertile of muscular strength, respectively. Low handgrip strength was significantly associated with all-cause mortality among older men and women from the general population after controlling for significant confounders. Hazard ratios (95% CI) comparing the first and second tertile to the third tertle were 3.33 (1.53–7.22) and 1.42 (0.61-3.28), respectively. Respective hazard ratios (95% CI) for mortality were higher in women than in men ((5.23 (0.67–40.91) and 2.17 (0.27–17.68) versus 2.36 (0.97–5.75) and 0.97 (0.36–2.57)).

Conclusions

Grip strength is inversely associated with mortality risk in older adults, and this association is independent of age, nutritional status, number of prescribed drugs, number of chronic diseases and level of physical activity. The association between muscular strength and all-cause mortality tended to be stronger in women. It seems to be particularly important for the weakest to enhance their levels of muscular strength in order to reduce the risk of dying early.

Spatial EMG potential distribution of biceps brachii muscle during resistance training and detraining

PURPOSE

We investigated the effect of resistance training and detraining on the spatial distribution pattern of surface electromyography (SEMG) of the biceps brachii.

METHODS

Ten male subjects completed 6 weeks of resistance training of one arm and 8 weeks of detraining. During training and detraining periods, spatial distribution patterns of SEMG were measured and quantified with 64 two-dimensional electrodes.

RESULTS

MVC, muscle thickness, and SEMG amplitude of the trained arm were significantly greater than those of the untrained arm after the 6 weeks of resistance training (p < 0.05), but these differences were no longer observed after 2 months of detraining. On the other hand, no significant differences in the spatial distribution pattern of SEMG were observed between the arms.

CONCLUSION

Spatial distribution pattern of SEMG was not changed during resistance training and detraining periods. This suggests that detectable adaptations in the motor unit recruitment pattern do not occur during regular resistance training.

The power of the mind: the cortex as a critical determinant of muscle strength/weakness

We tested the hypothesis that the nervous system, and the cortex in particular, is a critical determinant of muscle strength/weakness and that a high level of corticospinal inhibition is an important neurophysiological factor regulating force generation. A group of healthy individuals underwent 4 wk of wrist-hand immobilization to induce weakness. Another group also underwent 4 wk of immobilization, but they also performed mental imagery of strong muscle contractions 5 days/wk. Mental imagery has been shown to activate several cortical areas that are involved with actual motor behaviors, including premotor and M1 regions. A control group, who underwent no interventions, also participated in this study. Before, immediately after, and 1 wk following immobilization, we measured wrist flexor strength, voluntary activation (VA), and the cortical silent period (SP; a measure that reflect corticospinal inhibition quantified via transcranial magnetic stimulation). Immobilization decreased strength 45.1 ± 5.0%, impaired VA 23.2 ± 5.8%, and prolonged the SP 13.5 ± 2.6%. Mental imagery training, however, attenuated the loss of strength and VA by ∼50% (23.8 ± 5.6% and 12.9 ± 3.2% reductions, respectively) and eliminated prolongation of the SP (4.8 ± 2.8% reduction). Significant associations were observed between the changes in muscle strength and VA (r = 0.56) and SP (r = -0.39). These findings suggest neurological mechanisms, most likely at the cortical level, contribute significantly to disuse-induced weakness, and that regular activation of the cortical regions via imagery attenuates weakness and VA by maintaining normal levels of inhibition.

Greater glucose uptake heterogeneity in knee muscles of old compared to young men during isometric contractions detected by [(18)F]-FDG PET/CT

We used positron emission tomography/computed tomography (PET/CT) and [¹⁸F]-FDG to test the hypothesis that glucose uptake (GU) heterogeneity in skeletal muscles as a measure of heterogeneity in muscle activity is greater in old than young men when they perform isometric contractions. Six young (26 ± 6 years) and six old (77 ± 6 years) men performed two types of submaximal isometric contractions that required either force or position control. [¹⁸F]-FDG was injected during the task and PET/CT scans were performed immediately after the task. Within-muscle heterogeneity of knee muscles was determined by calculating the coefficient of variation (CV) of GU in PET image voxels within the muscles of interest. The average GU heterogeneity (mean ± SD) for knee extensors and flexors was greater for the old (35.3 ± 3.3%) than the young (28.6 ± 2.4%) (P = 0.006). Muscle volume of the knee extensors were greater for the young compared to the old men (1016 ± 163 vs. 598 ± 70 cm³, P = 0.004). In a multiple regression model, knee extensor muscle volume was a predictor (partial r = −0.87; P = 0.001) of GU heterogeneity for old men (R² = 0.78; P < 0.001), and MVC force predicted GU heterogeneity for young men (partial r = −0.95, P < 0.001). The findings demonstrate that GU is more spatially variable for old than young men and especially so for old men who exhibit greater muscle atrophy.

Cortical inhibition is reduced following short-term training in young and older adults

The purpose of this study was to investigate age-related differences in short-term training adaptations in cortical excitability and inhibition. Thirty young (21.9 ± 3.1 years) and 30 older (72.9 ± 4.6 years) individuals participated in the study. Each participant was randomly assigned to a control (n = 30) or a resistance training (n = 30) group, with equal numbers of young and older subjects in each group. Participants completed 2 days of testing, separated by 2 weeks during which time the training group participated in resistance training of the ankle dorsiflexor muscles three times per week. During each testing session, transcranial magnetic stimulation was used to generate motor evoked potentials (MEPs) and silent periods in the tibialis anterior. Hoffmann reflexes (H-reflexes) and compound muscle action potentials (M-waves) were also evoked via electrical stimulation of the peroneal nerve. At baseline, young subjects had higher maximum voluntary contraction (MVC) force (p = 0.002), larger M-wave amplitude (p < 0.001), and longer duration silent periods (p = 0.01) than older individuals, with no differences in the maximal amplitude of the MEP (p = 0.23) or H-reflex (p = 0.57). In the trained group, MVC increased in both young (17.4 %) and older (19.8 %) participants (p < 0.001), and the duration of the silent period decreased by ~15 and 12 ms, respectively (p < 0.001). Training did not significantly impact MEP (p = 0.69) or H-reflex amplitudes (p = 0.38). There were no significant changes in any measures in the control group (p ≥ 0.19) across the two testing sessions. These results indicate that a reduction in cortical inhibition may be an important neural adaptation in response to training in both young and older adults.

Effect of strength training on rate of force development in older women

We analyzed the effect of an 8-week strength training (ST) program on the rate of force development (RFD) and electromyographic activity (EMG) in older women. Seventeen women (M age = 63.4 years, SD = 4.9) without previous ST experience were randomly assigned to either a control (n=7) or training (n=10) group. A leg-press isometric test was used for assessment. ST (three sessions/ week, three sets of 10-12 repetition maximum, five different exercises) induced significant increases (p < .05) on peak RPD (48.4%) and on RFD) and EMG of vastus medialis at time intervals of 0-50, 0-100, 0-150, and 0-200 ms (41.1-69.2% and 43.8-64.3%, respectively). Therefore, ST resulted in favorable changes in neuromuscular responses in older women.

Progressive resistance exercise and Parkinson's disease: a review of potential mechanisms

This paper reviews the therapeutically beneficial effects of progressive resistance exercise (PRE) on Parkinson's disease (PD). First, this paper discusses the rationale for PRE in PD. Within the first section, the review discusses the central mechanisms that underlie bradykinesia and muscle weakness, highlights findings related to the central changes that accompany PRE in healthy individuals, and extends these findings to individuals with PD. It then illustrates the hypothesized positive effects of PRE on nigro-striatal-thalamo-cortical activation and connectivity. Second, it reviews recent findings of the use of PRE in individuals with PD. Finally, knowledge gaps of using PRE on individuals with PD are discussed along with suggestions for future research.

Spatial EMG potential distribution pattern of vastus lateralis muscle during isometric knee extension in young and elderly men

The aim of the present study was to compare spatial electromyographic (EMG) potential distribution during force production between elderly and young individuals using multi-channel surface EMG (SEMG). Thirteen elderly (72-79years) and 13 young (21-27years) healthy male volunteers performed ramp submaximal contraction during isometric knee extension from 0% to 65% of maximal voluntary contraction. During contraction, multi-channel EMG was recorded from the vastus lateralis muscle. To evaluate alteration in heterogeneity and pattern in spatial EMG potential distribution, coefficient of variation (CoV), modified entropy and correlation coefficients with initial torque level were calculated from multi-channel SEMG at 5% force increment. Increase in CoV and decrease in modified entropy of RMS with increase of exerted torque were significantly smaller in elderly group (p<0.05) and correlation coefficients with initial torque level were significantly higher in elderly group than in young group at moderate torque levels (p<0.05). These data suggest that the increase of heterogeneity and the change in the activation pattern are smaller in elderly individuals than in young individuals. We speculated that multi-channel SEMG pattern in elderly individual reflects neuromuscular activation strategy regulated predominantly by clustering of similar type of muscle fibers in aged muscle.

Sarcopenia and obesity

Four body composition phenotypes exist in older adults: normal, sarcopenic, obese, and a combination of sarcopenic and obese. There is no consensus, however, on the definitions and classifications of these phenotypes and their etiology and consequences continue to be debated. The lack of standard definitions, particularly for sarcopenia and sarcopenic obesity, creates challenges for determining prevalence across different populations. The etiology of these phenotypes is multifactorial with complex covariate relationships. This review focuses on the current literature addressing the classification, prevalence, etiology, and correlates of sarcopenia, obesity, and the combination of sarcopenia and obesity, referred to as sarcopenic obesity.

Age-associated changes in motor unit physiology: observations from the Baltimore Longitudinal Study of Aging

OBJECTIVE

To examine motor unit characteristics (size and firing rate) associated with aging.

DESIGN

Cross-sectional, observational.

SETTING

Community.

PARTICIPANTS

Baltimore Longitudinal Study of Aging participants (N=102), aged 22.2 to 94.1 years, were studied.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Surface-represented motor unit size and firing rate were collected from the vastus medialis during knee extension at 10%, 20%, 30%, and 50% of each subject's maximum isometric voluntary contraction (MVC).

RESULTS

MVC declined with older age (P<.0001). Adjusting for differences in MVC, both firing rate and motor unit size per newton force generated began to increase in the 6th decade of life. Motor unit size increased per newton force to a greater extent than firing rate. Those over the age of 75 years also activated significantly larger motor units per unit force (P=.04). Relative to force generated, the average firing rate began increasing at 57.8+/-3.4 years and between 50.2 and 56.4 years (+/-4y) for motor unit size.

CONCLUSIONS

The size of motor units and firing rates used to achieve a given force changes with age, particularly after middle age. Whether these changes precede, follow, or occur concurrent to age-related modifications in muscle structure and contractile properties or sarcopenia is not known.

THE EFFECT OF PHYSICAL TRAINING ON THE LOCOMOTOR APPARATUS IN ELDERLY PEOPLE

Physiological changes taking place on the locomotive apparatus as a result of aging, such as muscular mass loss, body balance loss, reduced bone mass and osteoarthrosis cause limitations to the daily activities of elderly people, compromising their quality of life and making them weaker and dependent. Aged people who regularly practice physical activities have a higher level of functional independence and a better quality of life than the sedentary ones. This article addresses the key physiological changes with aging and provides a review of current literature about the effects of physical exercises on the locomotive apparatus of elderly individuals, specifying the best ways to prescribe physical exercises to this age group.

Age-related change in duration of afterhyperpolarization of human motoneurones

Motor unit (MU) potentials were recorded from brachial biceps of healthy subjects aged 5.5-79 years. The subjects were subdivided into young (5.5-19 year) and adult (37.5-79 year) groups, between which single MU discharge characteristics were compared. Firing rates were in the ranges of 8.3-21.7 s(-1) (mean 12.87 s(-1)) and 5.9-18.7 s(-1) (mean 11.08 s(-1)) for young and adult groups, respectively. Standard deviations (s.d.) of interspike intervals (ISIs) were in the range 4.84-11.57 ms (mean 8.39 ms) for the young group and 4.26-12.23 ms (mean 7.76 ms) for the adult group. Both differences were statistically significant (P < 0.001). Special attention was paid to the previously developed method of ISI variability analysis, which enabled the comparison of MUs with respect to afterhyperpolarization (AHP) duration of their motoneurones (MNs). The results show that AHP duration increases gradually with increasing age, which is in line with the transformation of muscle properties towards a slower phenotype. This transformation seems to be a continuous process, covering the entire lifespan of a human being, from childhood to senescence. The results presented here are significant for their insight into the ageing process of the neuromuscular system. The age-related change in AHP duration has not been investigated previously in human studies and has been met with ambiguous results in animal studies.

Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee

OBJECTIVE

To assess characteristics of active motor units (MUs) during volitional vastus medialis (VM) activation in adults with symptomatic knee osteoarthritis (OA) across the spectrum of radiographic severity and age-comparable healthy control volunteers.

METHODS

We evaluated 39 participants (age 65+/-3 years) in whom weight-bearing knee X-rays were assigned a Kellgren & Lawrence (KL) grade (18 with KL grade=0; four each with KL grades=1, 2 and 4; nine with grade 3). Electromyography (EMG) signals were simultaneously acquired using surface [surface EMG (S-EMG)] and intramuscular needle electrodes, and analyzed by decomposition-enhanced spike-triggered averaging to obtain estimates of size [surface-represented MU action potentials (S-MUAP) area], number [MU recruitment index (MURI)] and firing rates [MU firing rates (mFR)] of active MUs at 10%, 20%, 30% and 50% effort relative to maximum voluntary force [maximal voluntary isometric contraction (MVIC)] during isometric knee extension.

RESULTS

Knee extensor MVIC was lower in OA participants, especially at higher KL grades (P=0.05). Taking the observed force differences into account, OA was also associated with activation of larger MUs (S-MUAP area/MVICx%effort; P<0.0001). In contrast, the estimated number of active units (MURI/MVICx%effort) changed differently as effort increased from 10% to 50% and was higher with advanced OA (KL=3, 4) than controls (P=0.0002).

CONCLUSION

VM activation changes at the level of the MU with symptomatic knee OA, and this change is influenced by radiographic severity. Poor muscle quality may explain the pattern observed with higher KL grades, but alternative factors (e.g., nerve or joint injury, physical inactivity or muscle composition changes) should be examined in early OA.

Training for older adults

Aging is associated with a reduction in physical fitness, with loss of muscular force and endurance. Physical activity has been demonstrated to provide substantial health benefits and to maintain functional independence and improve quality of life in older adults. Resistance training has a significant effect on muscle mass and force whereas endurance training increases oxygen transport and consumption capacities. This article presents training methods used in the literature and their associated effects in order to adapt training protocols to older populations. To maximise benefits from adoption of a program to which the patient can adhere for long time, it is important to tailor the exercise prescription to the individual.

Modulation of motor unit firing rates during a complex sinusoidal force task in young and older adults

This study compared motor unit rate coding and muscular force control in the first dorsal interosseous muscle of older ( n = 11, mean 72.3 yr) and young ( n = 12, mean 18.7 yr) adults. Rate coding during a sinusoidal isometric force-matching task was evaluated using spectral analysis of the time-varying changes in firing rate. The task required force modulations to match a trajectory comprising the sum of 0.15- and 0.45-Hz sine waves. Based on the amplitude of spectral peaks at 0.15 and 0.45 Hz, the amplitude of force modulation was similar in young and older adults at both frequencies ( F = 1.9, P = 0.17). Force modulation gain (FMG) was computed as the ratio of the amplitude of force modulation to the amplitude of firing rate modulation. To account for rate coding differences related to the properties of the motoneuron, recruitment threshold force was used as a covariate in age-group comparisons. At both task frequencies, firing rate was modulated with less amplitude ( F = 0 14, P < 0.001) and FMG was greater ( F = 0 27, P < 0.001) in the older adults. In its transformation of neural input to mechanical output, muscle is known to act as a low-pass filter. Compared with modulation at 0.15 Hz, less change in force per change in firing rate at 0.45 Hz (lower FMG; F = 0 67, P < 0.001), independent of age group, is consistent with this filtering effect. Our conclusion is that there is a reduced amplitude of firing rate modulation in older adults.