Age-related changes in motor unit function

Association of Handgrip Strength and Cardiovascular Disease Risk Among Middle-Aged Postmenopausal Women: An Analysis of the Korea National Health and Nutrition Examination Survey 2014-2019

Purpose

Handgrip strength is an indicator of overall muscle strength and has been associated with an increased risk of cardiovascular disease. Evidence suggests that menopause is a risk factor for cardiovascular disease in women, and muscle strength decreases progressively after menopause. Despite the prognostic importance of the decline in muscle strength and increased cardiovascular disease risk among postmenopausal women, evidence of their association is limited. This study aimed to investigate the relationship between handgrip strength and cardiovascular disease risk among postmenopausal, middle-aged Korean women.

Patients and Methods

Using pooled cohort equations, we calculated the 10-year risk of atherosclerotic cardiovascular disease (ASCVD) among postmenopausal women (N = 2019) aged 50-64 years without cardiovascular disease history from the 2014-2019 Korea National Health and Nutrition Examination Survey. Relative grip strength was defined as measured grip strength divided by body mass index. Logistic regression analysis of a complex sampling design was performed to evaluate the association between relative grip strength and a predicted 10-year ASCVD risk ≥7.5%.

Results

The average handgrip strength was 24.8 kg, and 5.2% of women were considered for sarcopenia (<18 kg). The quartile-stratified relative grip strength was negatively associated with 10-year ASCVD risk (p < 0.001). In the multiple logistic regression analysis, the adjusted odds ratio for the highest relative grip strength quartile was 0.53 (95% confidence interval [CI]: 0.36-0.78), and that of the group who breastfed for more than 12 months was 1.75 (95% CI: 1.36-2.25) for 10-year ASCVD risk.

Conclusion

Increased handgrip strength may be associated with lower cardiovascular disease risk among middle-aged postmenopausal women in Korea. Our findings provide critical evidence regarding the importance of increasing handgrip strength among postmenopausal, middle-aged women to reduce cardiovascular disease risk. Handgrip strength measurement might be a valuable screening tool for cardiovascular disease prevention.

Differences in acute neuromuscular response after single session of resistance exercise between young and older adults

AIMS

The purpose of this study was to investigate differences in the acute response after resistance exercise between young and older adults.

METHODS

Seventeen young and 18 older adults performed a single session of resistance exercise, consisting of 3 sets of 10 isometric knee extensions. Maximal voluntary contraction (MVC), motor unit (MU) activity of the vastus lateralis, and electrically elicited torque of the knee extensor were measured before and after the resistance exercise.

RESULTS

Although both groups showed the same degree of decline in MVC (young: -15.2 ± 14.3 %, older: -16.4 ± 7.9 %, p = 0.839), electrically elicited torque markedly decreased in the young group (young: -21.5 ± 7.7 %, older: -14.3 ± 9.5 %, p < 0.001), and the decrease in the MU firing rate was greater in the older group (young: -26.1 ± 24.1 %, older: -44.7 ± 24.5 %, p < 0.001). Changes in the MU firing rate following the exercise were correlated with the MU recruitment threshold in the older group (p < 0.001, rs = 0.457), but not young group (p = 0.960).

DISCUSSION

These results showed that young adults exhibited a greater acute response in the peripheral component, whereas older adults showed a greater acute response in the central component of the neuromuscular system, and the acute response in MUs with a high recruitment threshold following resistance exercise was smaller than in those with a low recruitment threshold in older adults. These findings may partly explain why there are different chronic adaptations to resistance training between young and older adults.

Visual Information Processing in Older Adults: Force Control and Motor Unit Pool Modulation

Increased visual information about a task impairs force control in older adults. To date, however, it remains unclear how increased visual information changes the activation of the motor unit pool differently for young and older adults. Therefore, this study aimed to determine how increased visual information alters the activation of the motor neuron pool and influences force control in older adults. Fifteen older adults (66-86 years, seven women) and fifteen young adults (18-30 years, eight women) conducted a submaximal constant force task (15% of maximum) with ankle dorsiflexion for 20 s. The visual information processing was manipulated by changing the amount of force visual feedback into a low-gain (0.05°) or high-gain (1.2°) condition. Older adults exhibited greater force variability, especially at high-gain visual feedback. This exacerbated force variability from low- to high-gain visual feedback was associated with modulations of multiple motor units, not single motor units. Specifically, increased modulation of multiple motor units from 10 to 35 Hz may contribute to the amplification in force variability. Therefore, our findings suggest evidence that high-gain visual feedback amplifies force variability of older adults which is related to increases in the activation of motor neuron pool from 10 to 35 Hz.

Regional recruitment and differential behavior of motor units during postural control in older adults

Aging is associated with neuromuscular system changes that may have implications for the recruitment and firing behaviors of motor units (MUs). In previous studies, we observed that young adults recruit subpopulations of triceps surae MUs during tasks that involved leaning in five directions: common units that were active during different leaning directions and unique units that were active in only one leaning direction. Furthermore, the MU subpopulation firing behaviors [average firing rate (AFR), coefficient of variation (CoVISI), and intermittent firing] modulated with leaning direction. The purpose of this study was to examine whether older adults exhibited this regional recruitment of MUs and firing behaviors. Seventeen older adults (aged 74.8 ± 5.3 yr) stood on a force platform and maintained their center of pressure leaning in five directions. High-density surface electromyography recordings from the triceps surae were decomposed into single MU action potentials. A MU tracking analysis identified groups of MUs as being common or unique across the leaning directions. Although leaning in different directions did not affect the AFR and CoVISI of common units (P > 0.05), the unique units responded to the leaning directions by increasing AFR and CoVISI, albeit modestly (F = 18.51, P < 0.001). The unique units increased their intermittency with forward leaning (F = 9.22, P = 0.003). The mediolateral barycenter positions of MU activity in both subpopulations were found in similar locations for all leaning directions (P > 0.05). These neuromuscular changes may contribute to the reduced balance performance seen in older adults.NEW & NOTEWORTHY In this study, we observed differences in motor unit recruitment and firing behaviors of distinct subpopulations of motor units in the older adult triceps surae muscle from those observed in the young adult. Our results suggest that the older adult central nervous system may partially lose the ability to regionally recruit and differentially control motor units. This finding may be an underlying cause of balance difficulties in older adults during directionally challenging leaning tasks.

The larval midgut of Anopheles, Aedes, and Toxorhynchites mosquitoes (Diptera, Culicidae): a comparative approach in morphophysiology and evolution

The mosquito larval midgut is responsible for acquiring and storing most of the nutrients that will sustain the events of metamorphosis and the insect's adult life. Despite its importance, the basic biology of this larval organ is poorly understood. To help fill this gap, we carried out a comparative morphophysiological investigation of three larval midgut regions (gastric caeca, anterior midgut, and posterior midgut) of phylogenetically distant mosquitoes: Anopheles gambiae (Anopheles albimanus was occasionally used as an alternate), Aedes aegypti, and Toxorhynchites theobaldi. Larvae of Toxorhynchites mosquitoes are predacious, in contrast to the other two species, that are detritivorous. In this work, we show that the larval gut of the three species shares basic histological characteristics, but differ in other aspects. The lipid and carbohydrate metabolism of the An. gambiae larval midgut is different compared with that of Ae. aegypti and Tx. theobaldi. The gastric caecum is the most variable region, with differences probably related to the chemical composition of the diet. The peritrophic matrix is morphologically similar in the three species, and processes involved in the post-embryonic development of the organ, such as cell differentiation and proliferation, were also similar. FMRF-positive enteroendocrine cells are grouped in the posterior midgut of Tx. theobaldi, but individualized in An. gambiae and Ae. aegypti. We hypothesize that Tx. theobaldi larval predation is an ancestral condition in mosquito evolution.

Clinical-grade human umbilical cord-derived mesenchymal stem cells improved skeletal muscle dysfunction in age-associated sarcopenia mice

With the expansion of the aging population, age-associated sarcopenia (AAS) has become a severe clinical disease of the elderly and a key challenge for healthy aging. Regrettably, no approved therapies currently exist for treating AAS. In this study, clinical-grade human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) were administrated to two classic mouse models (SAMP8 mice and D-galactose-induced aging mice), and their effects on skeletal muscle mass and function were investigated by behavioral tests, immunostaining, and western blotting. Core data results showed that hUC-MSCs significantly restored skeletal muscle strength and performance in both mouse models via mechanisms including raising the expression of crucial extracellular matrix proteins, activating satellite cells, enhancing autophagy, and impeding cellular aging. For the first time, the study comprehensively evaluates and demonstrates the preclinical efficacy of clinical-grade hUC-MSCs for AAS in two mouse models, which not only provides a novel model for AAS, but also highlights a promising strategy to improve and treat AAS and other age-associated muscle diseases. This study comprehensively evaluates the preclinical efficacy of clinical-grade hUC-MSCs in treating age-associated sarcopenia (AAS), and demonstrates that hUC-MSCs restore skeletal muscle strength and performance in two AAS mouse models via raising the expression of extracellular matrix proteins, activating satellite cells, enhancing autophagy, and impeding cellular aging, which highlights a promising strategy for AAS and other age-associated muscle diseases.

Muscle fiber type grouping does not change in response to prolonged resistance exercise training in healthy older men

BACKGROUND

Ageing of skeletal muscle is characterized in some by muscle fiber type grouping due to denervation-reinnervation cycles, but the severity of fiber type grouping varies widely across individuals of the same chronological age. It remains unknown whether fiber type grouping is associated with lower muscle mass and/or reduced physical function in elderly. Therefore, we assessed the relationship between fiber type grouping and indices of muscle mass and physical function in older adults. In addition, we assessed whether fiber type grouping is affected by prolonged resistance training in older adults.

METHODS

Twenty young (21 ± 2 y) and twenty older (70 ± 4 y) healthy men participated in the present study. Body composition (DXA-scan), quadriceps cross-sectional area (CT-scan) and muscle strength (1RM) were assessed at baseline (young and old) and following 12 weeks of resistance training (old only). Percutaneous skeletal muscle biopsies from the vastus lateralis were collected at baseline (young and old) and following exercise training (old only). Immunohistochemical analyses were performed to evaluate type I and type II muscle fiber distribution, size, myonuclear content and grouping.

RESULTS

At baseline, type II fibers were significantly (P < 0.05) smaller in older compared with young adults (5366 ± 1288 vs 6705 ± 1168 μm²). Whereas no differences were observed in type I, type II fiber grouping was significantly (P < 0.05) lower in older (18 ± 18 %) compared with young (32 ± 25 %) men. No significant correlations were observed between fiber type grouping and muscle mass or physical function. Prolonged resistance training in old men resulted in a significant increase (P < 0.05) in type II fiber size (from 5366 ± 1288 to 6165 ± 1484 μm²) with no significant changes in the proportion of type I muscle fibers found grouped.

CONCLUSION

Muscle fiber type grouping is not associated with lower body strength or muscle mass in healthy, older men. In addition, twelve weeks of resistance exercise training results in type II muscle fiber specific hypertrophy but does not affect fiber type grouping.

Analysis of Vibration Frequency and Direction for Facilitating Upper-Limb Muscle Activity

We aimed to determine the effect of vibration frequency and direction on upper-limb muscle activation using a handheld vibrator. We recruited 19 healthy participants who were instructed to hold a handheld vibrator in their dominant hand and maintain the elbow at 90° flexion, while vertical and horizontal vibrations were applied with frequencies of 15, 30, 45, and 60 Hz for 60 s each. Surface electromyography (EMG) measured the activities of the flexor digitorum superficialis (FDS), flexor carpi radialis (FCR), extensor carpi ulnaris (ECU), extensor carpi radialis (ECR), biceps, triceps, and deltoid anterior muscles. EMG changes were evaluated as the difference in muscle activity between vibration and no-vibration (0 Hz) conditions. Muscle activity was induced under vibration conditions in both vertical and horizontal (p < 0.05) directions. At 45 Hz, FDS and FCR activities increased during horizontal vibrations, compared with those during vertical vibrations. ECU activity significantly increased under 15-Hz vertical vibrations compared with that during horizontal vibrations. Vibrations from the handheld vibrator significantly induced upper-limb muscle activity. The maximum muscle activations for FDS, ECR, ECU, biceps, and triceps were induced by 45-Hz horizontal vibration. The 60-Hz vertical and 30-Hz horizontal vibrations facilitated maximum muscle activations for the FCR and deltoid anterior, respectively.

Correlation Between Skin Autofluorescence and Muscle Activities of Lower Limb in Aging Without Disease and Disability

Skin autofluorescence is a useful index to estimate the accumulation of advanced glycation end-products in human tissues. Elderly persons with higher skin autofluorescence have lower muscle mass, muscle strength and muscle power, however, little is known about the relationship between the skin autofluorescence level and each muscle activity. We measured the values of skin autofluorescence from five places on a lower limb, and the signals of surface electromyogram during isometric contractions from five muscles on that, simultaneously. The waveforms of surface electromyogram were analyzed by Daubechies-4 wavelet transformation. The value of skin autofluorescence was increased in the proximal part of the lower limb compared with the value of the distal part. The principal component of surface electromyogram activity in a time-frequency domain was lower in the proximal part compared with that of the distal part. There was a weak negative correlation between the value of skin autofluorescence on the gluteal region and the value of the mean wavelet coefficient of the surface electromyogram signals within the gluteus maximus muscle. The higher accumulation of advanced glycation end-products on the gluteal region might suggest the lower muscle activity in aging without disease and disability.

Surface electromyographic activity of the erector spinae and multifidus during arm- and leg-ergometer exercises in young healthy men

Objectives: Ergometer exercise was considered a new loading method that can be used for participants who are unable to assume the core strengthening exercise posture commonly used to strengthen the erector spinae and multifidus. This study aimed to investigate with healthy participants whether arm and leg ergometers could be used for core strengthening exercises and whether different exercise sites would affect the results. Methods: The study was conducted with 15 healthy adult male participants aged 20-35 years. The intervention consisted of arm- and leg-ergometer exercises performed by the participants. The exercise protocol consisted of three 1-min sessions (rest, 50W, and 100 W), which were measured consecutively. Surface electromyography (sEMG) was measured during the sessions. Maximal voluntary contraction (MVC) of the erector spinae and multifidus was also measured, during which sEMG was measured. The sEMG during ergometer exercise was calculated as a percentage of the MVC (calculated as % MVC). The root mean square (RMS) was recorded from the sEMG activity. Muscle activity of the erector spinae and multifidus was compared between ergometer exercises and between intensity levels. Heart rate (HR) was recorded by electrocardiogram. Results: In the arm-ergometer exercise, the % MVC values of the erector spinae were 6.3 ± 3.1, 10.9 ± 5.4, and 16.9 ± 8.3% at rest, 50 W, and 100 W conditions, respectively. The multifidus was 4.6 ± 2.9, 9.2 ± 5.6, and 12.6 ± 7.6% at rest, 50 W, and 100 W conditions, respectively. The respective % MVC values during the leg-ergometer exercise were 3.8 ± 1.7, 7.2 ± 3.8, and 10.4 ± 4.0% at rest, 50 W, and 100 W conditions, respectively. Leg-ergometer exercises were 2.6 ± 2.1, 6.9 ± 5.7, and 10.3 ± 6.8% at rest, 50 W, and 100 W conditions, respectively. The activities of the two muscles increased at comparable levels with increased workload in both types of exercises (p < 0.01, each). HR increased with the increased workload and the increase was larger during arm-than leg-ergometer exercises. Conclusion: These results demonstrate that both arm- and leg-ergometer exercises are potentially alternative methods for erector spinae and multifidus training for healthy participants. Further research is needed to target elderly.

Nerve Conduction Study in Healthy Elderly Subjects in Central India: A Cross-Sectional Study

Background

There are many physiological changes that accompany aging. Slowing of muscle contraction, alteration of muscle metabolism and neuromuscular junction, and reduction of nerve conduction velocity (NCV) are among these physiological changes. The present study was conducted to elucidate the effect of physiological factors like gender, height, and Body Mass Index (BMI) on motor and sensory nerve conduction study (NCS) of the upper limb and find out the normal data for healthy elderly subjects in central India.

Methods

A cross-sectional study among 382 healthy adult participants of central India aged 60 years and above. The study was carried out in the department of Physiology, Acharya Vinoba Bhave Rural Hospital, Wardha, India, from July 2017 to June 2022. An NCS was performed using the Neuron Spectrum 5 machine (Neurosoft, Ivanovo, Russia). A Microsoft Excel spreadsheet (Microsoft Corporation, Redmond, Washington, United States) was used to tabulate the information gathered. For statistical analysis, IBM SPSS Statistics for Windows, Version 22.0 (Released 2013; IBM Corp., Armonk, New York, United States) was used.

Results

All NCS parameters were greater in males as compared to females. As age advances, longer distal motor latency (DML) and F-wave minimum latency, decreasing amplitude, and slowing of conduction velocity (CV) were observed. As height increases, increasing DML and F-wave minimum latency, decreasing amplitude, and slowing of CV were observed. Higher BMI was found to be associated with lower amplitudes and slowing of CVs.

Conclusion

Age and height have a negative influence on amplitude and CV is a positive influence on DML and F-min latency. Higher BMI has a negative influence on amplitude and CV.

Microscopic changes in the spinal extensor musculature in people with chronic spinal pain: a systematic review

BACKGROUND CONTEXT

Chronic spinal pain is one the most common musculoskeletal disorders. Previous studies have observed microscopic structural changes in the spinal extensor muscles in people with chronic spinal pain. This systematic review synthesizes and analyzes all the existing evidence of muscle microscopic changes in people with chronic spinal pain.

PURPOSE

To assess the microscopy of spinal extensor muscles including the fiber type composition, the area occupied by fiber types, fiber size/cross sectional area (CSA), and narrow diameter (ND) in people with and without chronic spinal pain. Further, to compare these outcome measures across different regions of the spine in people with chronic neck, thoracic and low back pain.

STUDY DESIGN

Systematic review with meta-analysis.

METHODS

MEDLINE (Ovid Interface), Embase, PubMed, CINAHL Plus, and Web of Science were searched from inception to October 2020. Key journals, conference proceedings, grey literature and hand searching of reference lists from eligible studies were also searched. Two independent reviewers were involved in the selection process. Only studies examining the muscle microscopy of the spinal extensor muscles (erector spinae [ES] and/or multifidus [MF]) between people with and without chronic spinal pain were selected. The risk of bias from the studies was assessed using modified Newcastle Ottawa Scale and the level of evidence was established using the GRADE approach. Data were synthesized based on homogeneity on the methodology and outcome measures of the studies for ES and MF muscles and only four studies were eligible for analysis.

RESULTS

All the five studies included were related to chronic low back pain (CLBP). Meta-analysis (inverse variance method for random effect to calculate mean difference and 95% CI) was performed for the ES fiber type composition by numbers for both type I and type II fibers (I²=43% and 0% respectively indicating homogeneity of studies) and showed no difference between the people with and without CLBP with an overall effect estimate Z= 1.49 (p=.14) and Z=1.06 (p=.29) respectively. Meta-analysis was performed for ES fiber CSA for both type I and type II fibers (I²=0 for both) and showed no difference between people with and without CLBP with an overall effect estimate Z=0.08 (p=.43) and Z=0.75 (p=.45) respectively. Analysis was not performed for ES area occupied by fiber types and ND due to heterogeneity of studies and lack of evidence respectively. Similarly, meta-analysis was not performed for MF fiber type composition by numbers due to heterogeneity of studies. MF analysis for area occupied by fiber type, fiber CSA and ND did not yield sufficient evidence.

CONCLUSIONS

For the ES muscle, there was no difference in fiber type composition and fiber CSA between people with and without CLBP and no conclusions could be drawn for ND for the ES. For the MF, no conclusions could be drawn for any of the muscle microscopy outcome measures. Overall, the quality of evidence is very low and there is very low evidence that there are no differences in microscopic muscle features between people with and without CLBP.

Cross-cultural adaptation into Italian and validation of the Frenchay dysarthria assessment - 2

BACKGROUND

A comprehensive evaluation of dysarthria is required to make an accurate differential diagnosis with other communication disorders and plan effective rehabilitation programs. The Frenchay Dysarthria Assessment-2 (FDA-2) is a valid, reliable and widely used protocol for the assessment of dysarthria. An Italian version of the FDA-2 is currently lacking.

AIM

To perform a cross-cultural adaptation of the FDA-2 in Italian and to validate the Italian version of the FDA-2.

DESIGN

Validation study.

SETTING

Inpatient rehabilitation center.

POPULATION

69 patients with dysarthria and 112 healthy controls.

METHODS

The FDA-2 was translated and cross-culturally adapted to Italian. The validation study was carried out in 4 steps: (1) 42 audio-recorded samples of FDA-2 items from 11 patients with dysarthria were independently assessed by 7 speech and language pathologists for interrater reliability and re-assessed after 6 weeks for intrarater reliability; (2) 11 patients were simultaneously assessed by 3 speech and language therapists for interrater reliability of the whole Italian version of the FDA-2 and re-assessed within 24 hours for test-retest reliability; (3) the Italian version of the FDA-2 was administered to 112 healthy volunteers to gain normative data; (4) 49 patients with different types of dysarthria were assessed using the Italian version of the FDA-2, the Therapy Outcome Measure impairment scale and the Robertson Profile for the validity analysis.

RESULTS

Interrater and intrarater reliability ranged from good to excellent (ICC >0.75) except for 3 audio-recorded items. The overall protocol demonstrated excellent (ICC >0.9) inter-rater and test-retest reliability for all the sections and the total score. Normative data were gained for 6 age groups. For the validity analysis, a statistically significant difference was found between dysarthric patients and healthy subjects for all sections and the total score. The FDA-2 significantly correlated to the therapy outcome measure (r=0.75) and the Robertson Profile (r=0.81).

CONCLUSIONS

The Italian version of the FDA-2 yield satisfactory reliability and validity, comparable to the psychometric properties of the original version.

CLINICAL REHABILITATION IMPACT

Speech and language pathologists can rely on a valid and reliable tool in Italian for the assessment of dysarthria in both clinical and research practice.

The association between heart rate behavior and gait performance: The moderating effect of frailty

Introduction

Research suggests that frailty not only influence individual systems, but also it affects the interconnection between them. However, no study exists to show how the interplay between cardiovascular and motor performance is compromised with frailty.

Aim

To investigate the effect of frailty on the association between heart rate (HR) dynamics and gait performance.

Methods

Eighty-five older adults (≥65 years and able to walk 9.14 meters) were recruited (October 2016—March 2018) and categorized into 26 non-frail (age = 78.65±7.46 years) and 59 pre-frail/frail individuals (age = 81.01±8.17) based on the Fried frailty phenotype. Participants performed gait tasks while equipped with a wearable electrocardiogram (ECG) sensor attached to the chest, as well as wearable gyroscopes for gait assessment. HR dynamic parameters were extracted, including time to peak HR and percentage increase in HR in response to walking. Using the gyroscope sensors gait parameters were recorded including stride length, stride velocity, mean swing velocity, and double support.

Results

Among the pre-frail/frail group, time to peak HR was significantly correlated with all gait parameters (p<0.0001, r = 0.51–0.59); however, for the non-frail group, none of the correlations between HR dynamics and gait performance parameters were significant (p>0.45, r = 0.03–0.15). The moderation analysis of time to peak HR, demonstrated a significant interaction effect of HR dynamics and frailty status on walking velocity (p<0.01), and the interaction effect was marginally non-significant for other gait parameters (p>0.10).

Conclusions

Current findings, for the first time, suggest that a compromised motor and cardiac autonomic interaction exist among pre-frail/frail older adults; an impaired HR performance (i.e., slower increase of HR in response to stressors) may lead to a slower walking performance. Assessing physical performance and its corresponding HR behavior should be studied as a tool for frailty screening and providing insights about the underlying cardiovascular-related mechanism leading to physical frailty.

Force Production and Coordination from Older Women in Water Fitness Exercises

The aim of this study was to compare bilateral propulsive forces and coordination while exercising at static and dynamic conditions in the water. A total of 27 older women (age: 65.1 ± 6.7 years old) performed the following exercises: (i) horizontal upper-limbs adduction (HA; static condition) and (ii) rocking horse (RH; dynamic condition) through an incremental protocol with music cadences from 105 up to 150 b·min⁻¹. The duration of each trial was set at 30 second (sec). Propulsive peak force (in Newton, N) of dominant (PF_D) and nondominant (PF_ND) upper limbs was retrieved using hand sensors coupled to a differential pressure system. Significant differences in force production were found between static and dynamic exercises at higher cadences (120, 135, and 150 b·min⁻¹). The static condition elicited higher bilateral propulsive forces and a more symmetric pattern. The in-water static exercise with bilateral action from the upper limbs proved to be the most appropriate strategy for older women to work strength and to reduce asymmetries.

Investigating the Stroke- and Aging-Related Changes in Global and Instantaneous Intermuscular Coupling Using Cross-Fuzzy Entropy

Intermuscular coupling is essential in the coordination of agonist and antagonist muscles. However, its dynamic characteristics are not fully understood, especially the alterations of intermuscular coupling induced by stroke and aging. This study aimed to investigate the aging- and stroke-related changes in the global and instantaneous intermuscular coupling between agonist and antagonist muscles. In the experiment, 8 patients after stroke, 18 healthy young subjects and 10 healthy middle-aged subjects were recruited and instructed to finish the elbow flexion and extension tasks. Cross-fuzzy entropy (C-FuzzyEn) and instantaneous C-FuzzyEn ( [Formula: see text]-FuzzyEn) based on a sliding window were used to analyze the global and instantaneous intermuscular coupling, respectively. Instantaneous FuzzyEn ( i -FuzzyEn) based on a sliding window was also applied to investigate the dynamic complexity of the EMG segment. Pearson correlation analysis revealed that i -FuzzyEn values were negatively correlated with [Formula: see text]-FuzzyEn values in most cases, which implied that there was a positive correlation between EMG complexity and intermuscular coupling. The C-FuzzyEn values between agonist and antagonist muscles increased significantly in both tasks of the patients after stroke than those of the healthy subjects (p < 0.05), which might be due to the decrease in intermuscular coupling induced by the damage of the corticospinal pathways after stroke. The combined application of C-FuzzyEn, [Formula: see text]-FuzzyEn and i -FuzzyEn provides a more comprehensive understanding of the global and instantaneous intermuscular coupling.

Neuroprotective effects of exercise on the aging human neuromuscular system

Human biological aging from maturity to senescence is associated with a gradual loss of muscle mass and neuromuscular function. It is not until very old age (>80 years) however, that these changes often manifest into functional impairments. A driving factor underlying the age-related loss of muscle mass and function is the reduction in the number and quality of motor units (MUs). A MU consists of a single motoneuron, located either in the spinal cord or the brain stem, and all of the muscle fibres it innervates via its peripheral axon. Throughout the adult lifespan, MUs are slowly, but progressively lost. The compensatory process of collateral reinnervation attempts to recapture orphaned muscle fibres following the death of a motoneuron. Whereas this process helps mitigate loss of muscle mass during the latter decades of adult aging, the neuromuscular system has fewer and larger MUs, which have lower quality connections between the axon terminal and innervated muscle fibres. Whether this process of MU death and degradation can be attenuated with habitual physical activity has been a challenging question of great interest. This review focuses on age-related alterations of the human neuromuscular system, with an emphasis on the MU, and presents findings on the potential protective effects of lifelong physical activity. Although there is some discrepancy across studies of masters athletes, if one considers all experimental limitations as well as the available literature in animals, there is compelling evidence of a protective effect of chronic physical training on human MUs. Our tenet is that high-levels of physical activity can mitigate the natural trajectory of loss of quantity and quality of MUs in old age.

Improper Remodeling of Organelles Deputed to Ca2+ Handling and Aerobic ATP Production Underlies Muscle Dysfunction in Ageing

Proper skeletal muscle function is controlled by intracellular Ca2+ concentration and by efficient production of energy (ATP), which, in turn, depend on: (a) the release and re-uptake of Ca2+ from sarcoplasmic-reticulum (SR) during excitation-contraction (EC) coupling, which controls the contraction and relaxation of sarcomeres; (b) the uptake of Ca2+ into the mitochondrial matrix, which stimulates aerobic ATP production; and finally (c) the entry of Ca2+ from the extracellular space via store-operated Ca2+ entry (SOCE), a mechanism that is important to limit/delay muscle fatigue. Abnormalities in Ca2+ handling underlie many physio-pathological conditions, including dysfunction in ageing. The specific focus of this review is to discuss the importance of the proper architecture of organelles and membrane systems involved in the mechanisms introduced above for the correct skeletal muscle function. We reviewed the existing literature about EC coupling, mitochondrial Ca2+ uptake, SOCE and about the structural membranes and organelles deputed to those functions and finally, we summarized the data collected in different, but complementary, projects studying changes caused by denervation and ageing to the structure and positioning of those organelles: a. denervation of muscle fibers-an event that contributes, to some degree, to muscle loss in ageing (known as sarcopenia)-causes misplacement and damage: (i) of membrane structures involved in EC coupling (calcium release units, CRUs) and (ii) of the mitochondrial network; b. sedentary ageing causes partial disarray/damage of CRUs and of calcium entry units (CEUs, structures involved in SOCE) and loss/misplacement of mitochondria; c. functional electrical stimulation (FES) and regular exercise promote the rescue/maintenance of the proper architecture of CRUs, CEUs, and of mitochondria in both denervation and ageing. All these structural changes were accompanied by related functional changes, i.e., loss/decay in function caused by denervation and ageing, and improved function following FES or exercise. These data suggest that the integrity and proper disposition of intracellular organelles deputed to Ca2+ handling and aerobic generation of ATP is challenged by inactivity (or reduced activity); modifications in the architecture of these intracellular membrane systems may contribute to muscle dysfunction in ageing and sarcopenia.

A TRIZ-driven conceptualisation of finger grip enhancer designs for the elderly

Background: Elderly people with severe finger weakness may need assistive health technology interventions. Finger weakness impedes the elderly in executing activities of daily living such as unbuttoning shirts and opening clothes pegs. While studies have related finger weakness with ageing effects, there appears to be no research that uses an algorithmic problem-solving approach such as the theory of inventive problem-solving (TRIZ) to recommend finger grip assistive technologies that resolve the issue of finger weakness among the elderly. Using TRIZ, this study aims to conceptualise finger grip enhancer designs for elderly people. Methods: Several TRIZ tools such as the cause-and-effect chain (CEC) analysis, engineering contradiction, physical contradiction, and substance-field analysis are used to conceptualise solutions that assist elderly people in their day-to-day pinching activities. Results: Based on the segmentation principle, a finger assistant concept powered by a miniature linear actuator is recommended. Specific product development processes are used to further conceptualise the actuation system. The study concluded that the chosen concept should use a DC motor to actuate fingers through tendon cables triggered by a push start button. Conclusions: Finger pinch degradation worsens the quality of life of the elderly. A finger grip enhancer that assists in day-to-day activities may be an effective option for elderly people, not only for their physical but also their mental well-being in society.

Age-Related Changes in Concentric and Eccentric Isokinetic Peak Torque of the Trunk Muscles in Healthy Older Versus Younger Men

This study investigated age-related changes in trunk muscle function in healthy men and the moderating effect of physical activity. Twelve older (67.3 ± 6.0 years) and 12 younger (24.7 ± 3.1 years) men performed isokinetic trunk flexion and extension tests across a range of angular velocities (15°/s-180°/s) and contractile modes (concentric and eccentric). For concentric trunk extension, mixed-effects analysis of covariance revealed a significant interaction between Angular velocity × Age group (p = .026) controlling for physical activity. Follow-up univariate analysis of covariance revealed that the younger group produced significantly greater peak torque for all concentric extension conditions. Eccentric trunk strength was somewhat preserved in the older group. Age-related changes in trunk strength were independent of physical activity. The normal loss of trunk muscle strength in older age is muscle- and contractile-mode specific. These findings provide guidance for effective intervention strategies to offset adverse health outcomes related to trunk strength loss in older adults.

The role of novel motor unit magnetic resonance imaging to investigate motor unit activity in ageing skeletal muscle

Sarcopenia is a progressive and generalized disease, more common in older adults, which manifests as a loss of muscle strength and mass. The pathophysiology of sarcopenia is still poorly understood with many mechanisms suggested. Age associated changes to the neuromuscular architecture, including motor units and their constituent muscle fibres, represent one such mechanism. Electromyography can be used to distinguish between different myopathies and produce counts of motor units. Evidence from electromyography studies suggests that with age, there is a loss of motor units, increases to the sizes of remaining units, and changes to their activity patterns. However, electromyography is invasive, can be uncomfortable, does not reveal the exact spatial position of motor units within muscle and is difficult to perform in deep muscles. We present a novel diffusion-weighted magnetic resonance imaging technique called 'motor unit magnetic resonance imaging (MUMRI)'. MUMRI aims to improve our understanding of the changes to the neuromuscular system associated with ageing, sarcopenia and other neuromuscular diseases. To date, we have demonstrated that MUMRI can be used to detect statistically significant differences in fasciculation rate of motor units between (n = 4) patients with amyotrophic lateral sclerosis (mean age ± SD: 53 ± 15) and a group of (n = 4) healthy controls (38 ± 7). Patients had significantly higher rates of fasciculation compared with healthy controls (mean = 99.1/min, range = 25.7-161.0 in patients vs. 7.7/min, range = 4.3-9.7 in controls; P < 0.05. MUMRI has detected differences in size, shape, and distribution of single human motor units between (n = 5) young healthy volunteers (29 ± 2.2) and (n = 5) healthy older volunteers (65.6 ± 14.8). The maximum size of motor unit territories in the older group was 12.4 ± 3.3 mm and 9.7 ± 2.7 mm in the young group; P < 0.05. MUMRI is an entirely non-invasive tool, which can be used to detect physiological and pathological changes to motor units in neuromuscular diseases. MUMRI also has the potential to be used as an intermediate outcome measure in sarcopenia trials.

Age-Related Change in Muscle Characteristics and Resistance Training for Older Adults

In older adults, muscle weakness contributes greatly to functional restrictions on daily living activities, increased risk of falls, and adverse physiological changes. It has been suggested that not only muscle mass but also muscular infiltration of noncontractile elements may influence muscular performance such as strength and rapid force production. It is proved that resistance training may provoke substantial increases in muscle size even if it is performed at low intensities in older individuals. Also, recent studies have demonstrated the effectiveness of resistance training on muscle quality such as muscular infiltration of noncontractile elements for older people. This review shows the age-related changes in muscle mass and muscle quality, which were measured by muscle echo intensity on ultrasound images, and low-intensity resistance training effects on muscle volume and muscle quality.

Associations of Oral Health-Related Quality of Life with age, oral status, and oral function among psychiatric inpatients in Japan: a cross-sectional study

BACKGROUND

As the general population of Japan ages, the population of hospitalized psychiatric patients is also ageing. The purpose of this study was to investigate the associations of oral health-related quality of life (OHRQoL) with age and oral health, including oral and swallowing function, among psychiatric inpatients.

METHODS

The subjects included 165 psychiatric inpatients in psychiatric hospitals in Japan. The General Oral Health Assessment Index (GOHAI) and the Eating Assessment Tool (EAT-10) were included in the questionnaire survey for the measurement of OHRQoL and the screening of dysphagia. A score ≥ 3 on the EAT-10 was defined as suspected dysphagia. Oral examinations and oral diadochokinesis (ODK) measurements for the tongue-lip motor function evaluation were conducted. The inpatients with acute psychiatric symptoms, moderate and severe dementia, and cognitive impairment that affected their ability to communicate and relate their feelings were excluded. A chi-squared test, the Mann-Whitney U test, and linear regression analysis were used for the analysis. The data were analysed at the 5% significance level.

RESULTS

A total of 100 (64.5%) psychiatric inpatients (mean age, 67.3 [SD, 14.5] years, 49% males, and 51% females) participated in this study. The means ± SDs for the decayed missing filled teeth (DMFT) index and GOHAI score were 20.6 ± 6 and 49.7 ± 7.9, respectively. The GOHAI score in the older age group (≥ 65 years) was significantly lower than that in the younger age group (< 65 years). The mean ODK scores were less than 3 times/s for all syllables. The percentage of the participants with suspected dysphagia was 45.0%. Tooth loss and suspected dysphagia were significantly associated with low GOHAI scores. The EAT-10 score was significantly correlated with the GOHAI score only after adjusting for age and sex (β = - 0.725, 95% CI - 0.97, - 0.64).

CONCLUSIONS

In hospitalized psychiatric patients, impaired oral health in the older subjects was more pronounced compared with that among general adults. Tooth loss and swallowing function were associated with OHRQoL. Therefore, oral care for the recovery of occlusal and swallowing functions may be needed to improve OHRQoL among psychiatric patients.

A Role of Lamin A/C in Preventing Neuromuscular Junction Decline in Mice

During aging, skeletal muscles become atrophic and lose contractile force. Aging can also impact the neuromuscular junction (NMJ), a synapse that transmits signals from motoneurons to muscle fibers to control muscle contraction. However, in contrast to muscle aging that has been studied extensively, less is known about the molecular mechanisms of NMJ aging although its structure and function are impaired in aged animals. To this end, we performed RNA sequencing (RNA-seq) analysis to identify genes whose expression in synapse-rich region is altered. Gene ontology (GO) analysis highlighted genes relating to nuclear structure or function. In particular, lamin A/C, an intermediate filament protein critical for the interphase nuclear architecture, was reduced. Remarkably, mutation of lamin A/C in muscles or motoneurons had no effect on NMJ formation in either sex of mice, but the muscle mutation caused progressive denervation, acetylcholine receptor (AChR) cluster fragmentation, and neuromuscular dysfunction. Interestingly, rapsyn, a protein critical to AChR clustering, was reduced in mutant muscle cells; and expressing rapsyn in muscles attenuated NMJ deficits of HSA-Lmna-/- mice. These results reveal a role of lamin A/C in NMJ maintenance and suggest that nuclear dysfunction or deficiency may contribute to NMJ deficits in aged muscles.SIGNIFICANCE STATEMENT This study provides evidence that lamin A/C, a scaffolding component of the nuclear envelope, is critical to maintaining the NMJ in mice. Its muscle-specific mutation led to progressive NMJ degeneration in vivo We showed that the mutation reduced the level of rapsyn, a protein necessary for acetylcholine receptor (AChR) clustering; and expression of rapsyn in muscles attenuated NMJ deficits of HSA-Lmna-/- mice. These results reveal a role of lamin A/C in NMJ maintenance and suggest that nuclear dysfunction or deficiency may contribute to NMJ deficits in aged muscles.

Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport

OBJECTIVE

To systematically review risk factors for hamstring strain injury (HSI).

DESIGN

Systematic review update.

DATA SOURCES

Database searches: (1) inception to 2011 (original), and (2) 2011 to December 2018 (update). Citation tracking, manual reference and ahead of press searches.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies presenting prospective data evaluating factors associated with the risk of index and/or recurrent HSI.

METHOD

Search result screening and risk of bias assessment. A best evidence synthesis for each factor and meta-analysis, where possible, to determine the association with risk of HSI.

RESULTS

The 78 studies captured 8,319 total HSIs, including 967 recurrences, in 71,324 athletes. Older age (standardised mean difference=1.6, p=0.002), any history of HSI (risk ratio (RR)=2.7, p<0.001), a recent HSI (RR=4.8, p<0.001), previous anterior cruciate ligament (ACL) injury (RR=1.7, p=0.002) and previous calf strain injury (RR=1.5, p<0.001) were significant risk factors for HSI. From the best evidence synthesis, factors relating to sports performance and match play, running and hamstring strength were most consistently associated with HSI risk. The risk of recurrent HSI is best evaluated using clinical data and not the MRI characteristics of the index injury.

SUMMARY/CONCLUSION

Older age and a history of HSI are the strongest risk factors for HSI. Future research may be directed towards exploring the interaction of risk factors and how these relationships fluctuate over time given the occurrence of index and recurrent HSI in sport is multifactorial.

Effect of age and sex on strength and spatial electromyography during knee extension

Background

Multichannel surface electromyography (EMG) is a method to examine properties of motor unit (MU) activity using multiple electrodes arranged on a two-dimensional grid. This technique can be used to examine alterations in EMG activity distribution due to contraction intensity as well as due to physiological differences such as age or sex. Therefore, the purpose of this study was to compare strength and high-density surface EMG (HDsEMG) features during isometric and isokinetic knee extensions between older and younger men and women.

Methods

Twenty younger (ages 19–25 years) and twenty older (ages 64–78) men and women performed submaximal and maximal isometric (at a joint angle of 90°) and isokinetic knee extensions, while HDsEMG was recorded from the vastus lateralis. Spatial distribution was estimated using the root mean square (RMS), and 2-dimensional (2D) maps were developed to examine spatial features. Coefficient of variation (CV) and modified entropy were used to examine alterations in muscle heterogeneity and pattern. Peak torque and HDsEMG parameters were compared across age and gender.

Results

Younger males and females produced significantly higher mean torque than the older group (p < 0.001) for all contractions. Both age- and sex-related significant differences (p < 0.05) were found for EMG spatial features suggesting neuromuscular differences. Modified entropy was significantly higher and CV was lower for young females compared to young males (p < 0.05) across both isometric and isokinetic contractions.

Conclusions

We found that isometric and isokinetic knee extension strength, spatial distribution, and intensity differ as a function of age and sex during knee extensions. While there were no differences detected in entropy between age groups, there were sex-related differences in the younger age category. The lack of age-related differences in entropy was surprising given the known effects of aging on muscle fiber composition. However, it is often reported that muscle coactivation increases with age and this work was limited to the study of one muscle of the knee extensors (vastus lateralis) which should be addressed in future work. The findings suggest while both age and sex affect muscle activation, sex had a greater effect on heterogeneity. The results obtained will help to develop improved rehabilitation programs for aging men and women.

The Effect of Mental Fatigue on Neuromuscular Function is Similar in Young and Older Women

The purpose of this study was to examine the effect of a mentally fatiguing task on neuromuscular function in young and older women. Neuromuscular measures were obtained prior to and following 20 min of a mentally fatiguing task. Maximal force output significantly decreased after the mental fatigue task (p = 0.02) and this was not different between age groups (p = 0.32). Increases in cortical silent period duration approached significance in both young and older groups (p = 0.06), suggesting that mental fatigue may cause increased cortical inhibition. Measures of peripheral neuromuscular function (contractile properties of the muscle, M-wave) did not change (p ≥ 0.09), suggesting that changes in force production with mental fatigue are more likely due to supraspinal than peripheral mechanisms. These findings provide further evidence of an interaction between mental fatigue and physical function.

Age-related Deficits in Voluntary Activation: A Systematic Review and Meta-analysis

Whether there are age-related differences in neural drive during maximal effort contractions is not clear. This review determined the effect of age on voluntary activation during maximal voluntary isometric contractions. The literature was systematically reviewed for studies reporting voluntary activation quantified with the interpolated twitch technique (ITT) or central activation ratio (CAR) during isometric contractions in young (18-35 yr) and old adults (>60 yr; mean, ≥65 yr). Of the 2697 articles identified, 54 were eligible for inclusion in the meta-analysis. Voluntary activation was assessed with electrical stimulation and transcranial magnetic stimulation on five different muscle groups. Random-effects meta-analysis revealed lower activation in old compared with young adults (d = -0.45; 95% confidence interval, -0.62 to -0.29; P < 0.001), with moderate heterogeneity (52.4%). To uncover the sources of heterogeneity, subgroup analyses were conducted for muscle group, calculation method (ITT or CAR), and stimulation type (electrical stimulation or transcranial magnetic stimulation) and number (single, paired, or train stimulations). The age-related reduction in voluntary activation occurred for all muscle groups investigated except the ankle dorsiflexors. Both ITT and CAR demonstrated an age-related reduction in voluntary activation of the elbow flexors, knee extensors, and plantar flexors. ITT performed with paired and train stimulations showed lower activation for old than young adults, with no age difference for the single electrical stimulation. Together, the meta-analysis revealed that healthy older adults have a reduced capacity to activate some upper and lower limb muscles during maximal voluntary isometric contractions; however, the effect was modest and best assessed with at least paired stimulations to detect the difference.

Important roles of dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline in human nutrition and health

Taurine (a sulfur-containing β-amino acid), creatine (a metabolite of arginine, glycine and methionine), carnosine (a dipeptide; β-alanyl-L-histidine), and 4-hydroxyproline (an imino acid; also often referred to as an amino acid) were discovered in cattle, and the discovery of anserine (a methylated product of carnosine; β-alanyl-1-methyl-L-histidine) also originated with cattle. These five nutrients are highly abundant in beef, and have important physiological roles in anti-oxidative and anti-inflammatory reactions, as well as neurological, muscular, retinal, immunological and cardiovascular function. Of particular note, taurine, carnosine, anserine, and creatine are absent from plants, and hydroxyproline is negligible in many plant-source foods. Consumption of 30 g dry beef can fully meet daily physiological needs of the healthy 70-kg adult human for taurine and carnosine, and can also provide large amounts of creatine, anserine and 4-hydroxyproline to improve human nutrition and health, including metabolic, retinal, immunological, muscular, cartilage, neurological, and cardiovascular health. The present review provides the public with the much-needed knowledge of nutritionally and physiologically significant amino acids, dipeptides and creatine in animal-source foods (including beef). Dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline are beneficial for preventing and treating obesity, cardiovascular dysfunction, and ageing-related disorders, as well as inhibiting tumorigenesis, improving skin and bone health, ameliorating neurological abnormalities, and promoting well being in infants, children and adults. Furthermore, these nutrients may promote the immunological defense of humans against infections by bacteria, fungi, parasites, and viruses (including coronavirus) through enhancing the metabolism and functions of monocytes, macrophages, and other cells of the immune system. Red meat (including beef) is a functional food for optimizing human growth, development and health.

Metabolite Profiling Revealed That a Gardening Activity Program Improves Cognitive Ability Correlated with BDNF Levels and Serotonin Metabolism in the Elderly

Metabolomics is useful for evaluating the fundamental mechanisms of improvements in the health functions of the elderly. Additionally, gardening intervention as a regular physical activity for the elderly maintained and improved physical, psychology, cognitive, and social health. This study was conducted to determine whether the cognitive ability of the elderly is affected by participating in a gardening activity program as a physical activity with a metabolomic potential biomarker. The gardening program was designed as a low to moderate intensity physical activity for the elderly. Serum metabolites resulting from gardening were subjected to metabolite profiling using gas chromatography time-of-flight mass spectrometry and ultra-high-performance liquid chromatography-linear trap quadruple-orbitrap-mass spectrometry followed by multivariate analyses. The partial least squares-discriminant analysis showed distinct clustering patterns among the control, non-gardening, and gardening groups. According to the pathway analysis, tryptophan metabolism including tryptophan, kynurenine, and serotonin showed significantly distinctive metabolites in the gardening group. Brain-derived neurotrophic factor levels (BDNF) in the gardening group were significantly increased after the gardening program. Correlation map analysis showed that the relative levels of tryptophan metabolites were positively correlated with BDNF. Our results show that tryptophan, kynurenine, and serotonin may be useful as metabolic biomarkers for improved cognitive ability by the gardening intervention.

Playing Exergames Facilitates Central Drive to the Ankle Dorsiflexors During Gait in Older Adults; a Quasi-Experimental Investigation

Purpose

Gait training might be of particular importance to reduce fall risk in older adults. In the present study we explore the hypothesis that video game-based training will increase tibialis anterior (TA) muscle EMG-EMG coherence and relates to functional measures of lower limb control.

Methods

We focus on video game-based training performed in standing position, where the subjects have to lift their toes to place their feet on different target zones in order to successfully play the game. This type of training is hypothesized leading to progressive changes in the central motor drive to TA motor neurons and, consequently, improved control of ankle dorsiflexion during gait.

Results

Twenty older adults, 79 ± 8 years old, 13 females/7 males, participated. Results showed a significant difference against 0 in the experimental ΔPOST condition in dual-task walking and beta Frequency Of Interest (p = 0.002). Walking under dual task condition showed significant change over time in minimal Toe Clearance for both the left [χ²(2) = 7.46, p = 0.024, n = 20] and right [χ²(2) = 8.87, p = 0.012, n = 20] leg. No change in lower extremity function was detectable.

Conclusion

Overall we conclude that the initiation of an exergame-based training in upright standing position improves neural drive to the lower extremities in older adults, effects on minimal Toe Clearance and seems an acceptable form of physical exercise for this group.

Neural control properties of the external anal sphincter in young and elderly women

AIMS

The prevalence of fecal incontinence (FI) increases with age and affects more than 15% of the elderly population. Sarcopenia, skeletal muscle structural, and functional decline with aging, is known to be caused by neuromuscular dysfunction. However, age-related alterations of the neuromuscular function of the external anal sphincter (EAS) have not been studied. This study aims to quantitatively characterize the effect of aging on the EAS by assessing the firing patterns and size of motor unit action potential (MUAP) using high-density surface electromyography (HD-sEMG) recording and analysis techniques.

METHODS

Thirteen young (31.0 ± 3.6 years) and 14 elderly (64.3 ± 6.2 years) healthy women were recruited for this study. EMG activity of the EAS during maximal voluntary contraction was recorded by a 64-Channel, HD-sEMG intra-rectal probe. HD-sEMG signals were decomposed into MUAP spike trains to extract the firing rate and amplitudes thereof.

RESULTS

HD-sEMG decomposition was successfully performed. For the young and elderly groups, mean motor unit (MU) firing rates of 11.4 ± 2.1 pulses per second (PPS) and 9.6 ± 2.3 PPS, and mean MUAP amplitudes of 45.2 ± 14.3 µV and 61.9 ± 21.2 µV were respectively obtained. Both the MU firing rate and MUAP amplitude were significantly different between two groups (P < .05). Moreover, the MUAP firing rate and amplitude correlated with age with a linear regression model (P < .05).

CONCLUSIONS

This study represents the first effort to examine the effect of aging on the neuromuscular function of EAS. Results suggest an age-related impairment of lower motor neuron descending excitation to the EAS with a compensatory increase in mean MU size.

Functional motor control deficits in older FMR1 premutation carriers

Individuals with fragile X mental retardation 1 (FMR1) gene premutations are at increased risk for fragile X-associated tremor/ataxia syndrome (FXTAS) during aging. However, it is unknown whether older FMR1 premutation carriers, with or without FXTAS, exhibit functional motor control deficits compared with healthy individuals. The purpose of this study, therefore, was to determine whether older FMR1 premutation carriers exhibit impaired ability to perform functional motor tasks. Eight FMR1 premutation carriers (age: 58.88 ± 8.36 years) and eight age- and sex-matched healthy individuals (60.13 ± 9.25 years) performed (1) a steady isometric force control task with the index finger at 20% of their maximum voluntary contraction (MVC) and; (2) a single-step task. During the finger abduction task, firing rate of multiple motor units of the first dorsal interosseous (FDI) muscle was recorded. Compared with healthy controls, FMR1 premutation carriers exhibited (1) greater force variability (coefficient of variation of force) during isometric force (1.48 ± 1.02 vs. 0.63 ± 0.37%; P = 0.04); (2) reduced firing rate of multiple motor units during steady force, and; (3) reduced velocity of their weight transfer during stepping (156.62 ± 26.24 vs. 191.86 ± 18.83 cm/s; P = 0.01). These findings suggest that older FMR1 premutation carriers exhibit functional motor control deficits that reflect either subclinical issues associated with premutations independent of FXTAS, or prodromal markers of the development of FXTAS.

Exploring the role of applied force eccentricity after foot-contact in managing anterior instability among older adults during compensatory stepping responses

BACKGROUND

The specific mechanisms responsible for age-related decline in forward stability control remain unclear. Previous work has suggested reactive control of net ground reaction force (GRF_net) eccentricity may be responsible for age-related challenges in mediolateral stability control during the restabilisation phase of forward compensatory stepping responses.

RESEARCH QUESTIONS

Does reactive control of GRF_net eccentricity play a role in managing forward stability control during the restabilisation phase of a forward stepping response to external balance perturbation?

METHODS

Healthy younger (YA) (n = 20) and older adults (OA) (n = 20) were tethered to a rigid frame, via adjustable cable. Participants were released from a standardised initial forward lean and regained their balance using a single step. Whole-body motion analysis and four force platforms were utilised for data acquisition. Forward instability was quantified as centre of mass (COM) incongruity - the difference between the first local peak and final stable anterior COM positions. The extent of GRF_net eccentricity was quantified as the sagittal-plane angle of divergence of the line of action of the GRF_net relative to the COM. Two discrete points during restabilisation were examined (P1 and P2), which have been suggested to be indicative of proactive and reactive COM control, respectively. Age-related differences in magnitude, timing and trial-to-trial variability of kinematic and kinetic outcome variables were analysed using two-factor ANOVAs with repeated-measures.

RESULTS

OA exhibited greater COM incongruity magnitude and variability - both were reduced with trial-repetition. There were no age-related differences in the magnitude or timing of P2. Instead, OA exhibited a reduced magnitude of GRF_net eccentricity at P1. There was a positive correlation between AP COM incongruity magnitude and P1 magnitude.

SIGNIFICANCE

Different from mediolateral stability control, the present results suggest that OA may experience forward stability control challenges as a function of insufficient preparatory lower limb muscle activation prior to foot-contact.

Mitochondrial Dysfunction in Skeletal Muscle Pathologies

Several molecular mechanisms are involved in the regulation of skeletal muscle function. Among them, mitochondrial activity can be identified. The mitochondria is an important and essential organelle in the skeletal muscle that is involved in metabolic regulation and ATP production, which are two key elements of muscle contractibility and plasticity. Thus, in this review, we present the critical and recent antecedents regarding the mechanisms through which mitochondrial dysfunction can be involved in the generation and development of skeletal muscle pathologies, its contribution to detrimental functioning in skeletal muscle and its crosstalk with other typical signaling pathways related to muscle diseases. In addition, an update on the development of new strategies with therapeutic potential to inhibit the deleterious impact of mitochondrial dysfunction in skeletal muscle is discussed.

Influence of aging and visual feedback on the stability of hand grip control in elderly adults

Aging causes a gradual decrease in maximal grip strength and leads many elderly people to have to rely on visual feedback to compensate for poorer muscle strength in performing daily activities and preventing accidents. Previous studies have investigated age and visual feedback-related changes in grip strength. However, little is known about methods of determining the quality and stability of hand grip strength control in the elderly, which is important for understanding their ability to generate grip force when handling objects with and without visual feedback in daily living. Therefore, the purpose of this study was to investigate the influence of aging and visual feedback on the stability of hand grip control in both hands in elderly adults. Forty-four healthy elderly persons (age 80.5 ± 4.53 years) and 36 young adults (age 32.69 ± 16.48 years) were recruited to execute grip force stability tasks using both hands at a 2 kg target force level. To perform the grip force stability task, the participants were asked to hold the dynamometer tightly in an attempt to achieve the target force level under visual and non-visual feedback conditions. Strength performances (grip force and coefficient of variation values) and stability of strength control (deviation error, variation error and force stability index values) for hand grip force stability tasks were calculated and analyzed. Compared with the visual feedback condition, the stability of grip force control in the hands of the young and elderly groups were significantly reduced in the non-visual feedback condition by 23.5%-57.1% (p < .05). The elderly group also showed significantly worse hand grip strength performances and stability of hand strength control than the young adult group (p < .05). Aging and non-visual feedback reduced the hand grip force output and stability of grip strength control of the hands. This may reveal the difficulty with manipulating hand-held objects in the absence of visual feedback while performing activities of daily living among the elderly.

The influence of knee extensor fatigue on lower extremity muscle activity during chair rise in young and older adults

PURPOSE

The purpose of this investigation was to evaluate alterations in muscular effort and temporal characteristics of their activity during the sit-to-stand (STS) due to isolated fatiguing of the knee extensors, as indicated by declines in torque output.

METHODS

Surface electromyography of the lower extremity was recorded in healthy young (n = 11) and older (n = 11) adults as they ascended from a seated position, before and after dynamic knee extension exercise.

RESULTS

Knee extensor fatigue caused significant increases in soleus, gastrocnemius, and gluteus maximus relative effort (%MVC) in both age groups during the STS task. Rectus femoris %MVCs in both young and older adults significantly increased to similar extents throughout the STS movement, whereas vastus lateralis amplitudes only increased in preparation for seat-off. Muscle temporal characteristics appeared to generally be invariant with fatigue, except for earlier activation onset for the ankle musculature in older adult participants.

CONCLUSIONS

These findings demonstrate that isolated knee extension fatiguing exercise caused compensatory changes in muscle activation patterns and increased reliance of non-fatigued muscles at the ankle and hip as well as increased activity of synergist muscles during the STS. Moreover, this occurred to similar extents in older adults who had lower knee extensor strengths and greater quadriceps %MVCs in comparison to their younger counterparts, regardless of fatigue condition.

Dysphagia Onset in Older Adults during Unrelated Hospital Admission: Quantitative Videofluoroscopic Measures

New-onset swallowing difficulties in older patients during unrelated hospital admissions are well recognized and may result in prolonged hospital stay and increased morbidity. Presbyphagia denotes age-related swallowing changes which do not necessarily result in pathological effects. The trajectory from presbyphagia to dysphagia is not well understood. This retrospective observational study compared quantitative videofluoroscopic measures in hospitalized older adults aged 70-100 years, reporting new dysphagia symptoms during admission (n = 52), to healthy asymptomatic older (n = 56) and younger adults (n = 43). Significant physiological differences seen in hospitalized older adults but not healthy adults, were elevated pharyngeal area (p < 0.001) and pharyngeal constriction ratio (p < 0.001). Significantly increased penetration (p < 0.001), aspiration (p < 0.001) and pharyngeal residue (p < 0.001) were also observed in the hospitalized older cohort. Reasons for onset of new swallow problems during hospitalization are likely multifactorial and complex. Alongside multimorbidity and polypharmacy, a combination of factors during hospitalization, such as fatigue, low levels of alertness, delirium, reduced respiratory support and disuse atrophy, may tip the balance of age-related swallowing adaptations and compensation toward dysfunctional swallowing. To optimize swallowing assessment and management for our aging population, care must be taken not to oversimplify dysphagia complaints as a characteristic of aging.

Sarcoglycan Alpha Mitigates Neuromuscular Junction Decline in Aged Mice by Stabilizing LRP4

During aging, acetylcholine receptor (AChR) clusters become fragmented and denervated at the neuromuscular junction (NMJ). Underpinning molecular mechanisms are not well understood. We showed that LRP4, a receptor for agrin and critical for NMJ formation and maintenance, was reduced at protein level in aged mice, which was associated with decreased MuSK tyrosine phosphorylation, suggesting compromised agrin-LRP4-MuSK signaling in aged muscles. Transgenic expression of LRP4 in muscles alleviated AChR fragmentation and denervation and improved neuromuscular transmission in aged mice. LRP4 ubiquitination was augmented in aged muscles, suggesting increased LRP4 degradation as a mechanism for reduced LRP4. We found that sarcoglycan α (SGα) interacted with LRP4 and delayed LRP4 degradation in cotransfected cells. AAV9-mediated expression of SGα in muscles mitigated AChR fragmentation and denervation and improved neuromuscular transmission in aged mice. These observations support a model where compromised agrin-LRP4-MuSK signaling serves as a pathological mechanism of age-related NMJ decline and identify a novel function of SGα in stabilizing LRP4 for NMJ stability in aged mice.SIGNIFICANCE STATEMENT This study provides evidence that LRP4, a receptor of agrin that is critical for NMJ formation and maintenance, is reduced at protein level in aged muscles. Transgenic expression of LRP4 in muscles ameliorates AChR fragmentation and denervation and improves neuromuscular transmission in aged mice, demonstrating a critical role of the agrin-LRP4-MuSK signaling. Our study also reveals a novel function of SGα to prevent LRP4 degradation in aged muscles. Finally, we show that NMJ decline in aged mice can be mitigated by AAV9-mediated expression of SGα in muscles. These observations provide insight into pathological mechanisms of age-related NMJ decline and suggest that improved agrin-LRP4-MuSK signaling may be a target for potential therapeutic intervention.

Relationships between muscle strength and multi-channel surface EMG parameters in eighty-eight elderly

Background

Since age-related muscle strength loss cannot be explained solely by muscle atrophy, other determinants would also contribute to muscle strength in elderly. The present study aimed to clarify contribution of neuromuscular activation pattern to muscle strength in elderly group. From 88 elderlies (age: 61~ 83 years), multi-channel surface electromyography (EMG) of the vastus lateralis muscle was recorded with two-dimensional 64 electrodes during isometric submaximal ramp-up knee extension to assess neuromuscular activation pattern. Correlation analysis and stepwise regression analysis were performed between muscle strength and the parameters for signal amplitude and spatial distribution pattern, i.e., root mean square (RMS), correlation coefficient, and modified entropy of multi-channel surface EMG.

Results

There was a significant correlation between muscle strength and RMS (r = 0.361, p = 0.001) in the elderly. Muscle thickness (r = 0.519, p < 0.001), RMS (r = 0.288, p = 0.001), and normalized RMS (r = 0.177, p = 0.047) were selected as major determinants of muscle strength in stepwise regression analysis (r = 0.664 in the selected model).

Conclusion

These results suggest that inter-individual difference in muscle strength in elderly can be partly explained by surface EMG amplitude. We concluded that neuromuscular activation pattern is also major determinants of muscle strength on elderly in addition to indicator of muscle volume.

The impact of Nordic walking training on the gait of the elderly

The purpose of the current study was to define the impact of regular practice of Nordic walking on the gait of the elderly. Thereby, we aimed to determine whether the gait characteristics of active elderly persons practicing Nordic walking are more similar to healthy adults than that of the sedentary elderly. Comparison was made based on parameters computed from three inertial sensors during walking at a freely chosen velocity. Results showed differences in gait pattern in terms of the amplitude computed from acceleration and angular velocity at the lumbar region (root mean square), the distribution (Skewness) quantified from the vertical and Euclidean norm of the lumbar acceleration, the complexity (Sample Entropy) of the mediolateral component of lumbar angular velocity and the Euclidean norm of the shank acceleration and angular velocity, the regularity of the lower limbs, the spatiotemporal parameters and the variability (standard deviation) of stance and stride durations. These findings reveal that the pattern of active elderly differs significantly from sedentary elderly of the same age while similarity was observed between the active elderly and healthy adults. These results advance that regular physical activity such as Nordic walking may counteract the deterioration of gait quality that occurs with aging.

Strength training increases skeletal muscle quality but not muscle mass in old institutionalized adults: a randomized, multi-arm parallel and controlled intervention study

BACKGROUND

Age related loss of skeletal muscle mass is accompanied by changes in muscle quality leading to impairment of functional status.

AIM

This study investigated the effect of resistance training and nutritional supply on muscle mass and muscle quality in very old institutionalized adults.

DESIGN

Prospective, randomized, multi-arm parallel and controlled intervention study.

SETTING

This study was conducted in five retirement care facilities.

POPULATION

This subgroup of the Vienna Active Ageing Study included 54 women and men (82.4±6.0 years) with impaired health status. Participants were randomly assigned either to elastic band resistance training (N.=16), training with nutritional supplementation (N.=21) or control group (N.=17).

METHODS

Health status was assessed at baseline with functional tests, cognitive status, nutritional status, sum of medications as well as sum of diseases. Skeletal muscle mass, determined by dual-energy X-ray absorptiometry, isokinetic knee extension and flexion force and handgrip strength were assessed at baseline and after 6 months. Muscle quality of lower extremities was defined as ratio of the extensor (MQ_LE (Ext.)) or flexor strength (MQ_LE (Flex.)) to lean leg mass. Muscle quality of upper extremity was defined as ratio of handgrip strength to lean arm mass. Follow-up examinations were performed after 12 and 18 months of intervention.

RESULTS

Muscle quality, but not muscle mass, showed significant correlations to functional tests at baseline (0.300 - 0.614, P<0.05). Resistance training significantly enhanced muscle quality of lower extremity after 6 months (MQ_LE (Ext.) +19.8%, MQ_LE (Flex.) +30.8%, P<0.05). Nutritional supplementation could not further increase the training effect. Participants with lower muscle quality at baseline benefit most from the training intervention. Skeletal muscle mass was not changed by any intervention.

CONCLUSIONS

Resistance training with elastic bands improved muscle quality in very old people. Additional nutritional supplementation was not able to further improve the effects obtained by training alone.

CLINICAL REHABILITATION IMPACT

Elastic band resistance training could be safely used to improve muscle quality even in old people with impaired health status. Weak and chronically ill participants benefit most from this training.

The role of thigh muscular efforts in limiting sit-to-stand capacity in healthy young and older adults

Aging is associated with an unavoidable decline in muscle mass, known as sarcopenia, leading to neuromuscular declines, muscle weakness, and subsequent disability. One particular measure utilized by rehabilitative professionals in evaluating functional declines in older persons is sit-to-stand (STS) capacity. The purpose of this investigation was to determine the role of activation intensity requirements of the thigh musculature in limiting a multi-joint STS endurance task. To do so, surface EMG signals of the quadriceps femoris (QF) and hamstrings (biceps femoris; BF) and their co-activation ratios (H:Q) were collected in young (18-35 years; n = 12) and older (60-75 years; n = 12) adult participants who repeatedly stood from a seated position until exhaustion. QF %MVIC was the sole predictor of total STS task times, as those who required the highest quadriceps efforts had the shortest task times. Moreover, older adult participants had significantly higher starting QF %MVIC as well as shorter task times. Interestingly, the H:Q ratio was not a significant predictor of STS capacities, nor did it differ between age groups or with fatigue. Results indicate that strengthening of the quadriceps to elevate or maintain strength reserves may improve an older adult's ability to perform multi-joint tasks repetitively throughout the day.

Trunk Muscle Training Augmented With Neuromuscular Electrical Stimulation Appears to Improve Function in Older Adults With Chronic Low Back Pain: A Randomized Preliminary Trial

OBJECTIVES

To assess the feasibility of a trial to evaluate a trunk muscle training program augmented with neuromuscular electrical stimulation (TMT+NMES) for the rehabilitation of older adults with chronic low back pain (LBP) and to preliminarily investigate whether TMT+NMES could improve physical function and pain compared with a passive control intervention.

MATERIALS AND METHODS

We conducted a single-blind, randomized feasibility trial. Patients aged 60 to 85 years were allocated to TMT+NMES (n=31) or a passive control intervention (n=33), consisting of passive treatments, that is, heat, ultrasound, and massage. Outcomes assessed 3- and 6-month postrandomization included Timed Up and Go Test, gait speed, pain, and LBP-related functional limitation.

RESULTS

Feasibility was established by acceptable adherence (≥80%) and attrition (<20%) rates for both interventions. Both groups had similar, clinically important reductions in pain of >2 points on a numeric pain rating scale during the course of the trial. But, only the TMT+NMES group had clinically important improvements in both performance-based and self-reported measures of function. In terms of the participants' global rating of functional improvement at 6 months, the TMT+NMES group improved by 73.9% and the passive control group improved by 56.7% compared with baseline. The between-group difference was 17.2% (95% confidence interval, 5.87-28.60) in favor of TMT+NMES.

DISCUSSION

It seems that a larger randomized trial investigating the efficacy of TMT+NMES for the purpose of improving physical function in older adults with chronic LBP is warranted.

AGE-RELATED DIFFERENCE IN DYNAMIC POSTURAL BALANCE AGAINST TILTING PERTURBATION IN MEN AND WOMEN

The aim of this study was to investigate how age and gender affect the dynamic postural balance during tilting perturbation. Fifty healthy subjects (15 young men, 13 young women, 11 elderly men and 11 elderly women) performed balance test on a movable force plate that tilted toe-up and toe-down. As outcome measures, maximum excursion and fluctuation were calculated from center of pressure (COP) data in the sagittal plane (anteroposterior). Two-way analysis of variance (ANOVA) and post-hoc comparisons were performed for the outcome measures with the independent factors of age and gender. The elderly had a greater COP maximum excursion as compared to the young during both perturbations ([Formula: see text]). COP fluctuation showed significant interaction of age and gender only in toe-up perturbation ([Formula: see text]). Especially, age-related difference existed only in women ([Formula: see text]). These results suggest that elderly women have dynamic balance strategy with great and fluctuated sway in response to toe-up perturbation. The age-related changes in dynamic balance among women may be related to the greater fall rate of elderly women.