The influence of aging on muscle strength and muscle fiber characteristics with special reference to eccentric strength

Stretch-shortening cycles protect against the age-related loss of power generation in rat single muscle fibres

Aging is associated with impaired strength and power during isometric and shortening contractions, however, during lengthening (i.e., eccentric) contractions, strength is maintained. During daily movements, muscles undergo stretch-shortening cycles (SSCs). It is unclear whether the age-related maintenance of eccentric strength offsets age-related impairments in power generation during SSCs owing to the utilization of elastic energy or other cross-bridge based mechanisms. Here we investigated how aging influences SSC performance at the single muscle fibre level and whether performing active lengthening prior to shortening protects against age-related impairments in power generation. Single muscle fibres from the psoas major of young (∼8 months; n = 31 fibres) and old (∼32 months; n = 41 fibres) male F344BN rats were dissected and chemically permeabilized. Fibres were mounted between a force transducer and length controller and maximally activated (pCa 4.5). For SSCs, fibres were lengthened from average sarcomere lengths of 2.5 to 3.0 μm and immediately shortened back to 2.5 μm at both fast and slow (0.15 and 0.60 Lo/s) lengthening and shortening speeds. The magnitude of the SSC effect was calculated by comparing work and power during shortening to an active shortening contraction not preceded by active lengthening. Absolute isometric force was ∼37 % lower in old compared to young rat single muscle fibres, however, when normalized to cross-sectional area (CSA), there was no longer a significant difference in isometric force between age groups, meanwhile there was an ∼50 % reduction in absolute power in old as compared with young. We demonstrated that SSCs significantly increased power production (75-110 %) in both young and old fibres when shortening occurred at a fast speed and provided protection against power-loss with aging. Therefore, in older adults during everyday movements, power is likely 'protected' in part due to the stretch-shortening cycle as compared with isolated shortening contractions.

Differences in Skeletal Muscle Fiber Characteristics Between Affected and Nonaffected Limbs in Individuals With Stroke: A Scoping Review

OBJECTIVE

The objective of this scoping review was to characterize and identify knowledge gaps about the changes in skeletal muscle fiber type proportion and cross-sectional area (CSA) after stroke.

METHODS

This scoping review followed previously proposed frameworks. A systematic search was conducted for articles examining muscle fiber type proportion and CSA in individuals with stroke in EMBASE, MEDLINE, PsycINFO, CINAHL, SPORTDiscus, and Web of Science databases from inception to December 20, 2022. Two independent authors screened and extracted the data. Results were discussed using theories proposed by the authors of the included studies.

RESULTS

Of 13 studies (115 participants), 6 (46%) were case studies or case series, 6 (46%) were cross-sectional studies, and 1 (8%) was an experimental study. Studies had small sample sizes (1-23 participants) and various muscle sampling sites (6 different muscles). All 13 studies examined muscle fiber type distributions, and 6 (46%) examined CSA. Ten (77%) studies examined differences between paretic and nonparetic muscles, and 5 (38%) compared people with stroke to people without stroke. Results from 9 of 13 studies (69%) supported a greater proportion of type II muscle fibers in the paretic limb. Of those, 4 studies (42 participants), 3 studies (17 participants), and 1 study (1 participant) saw no differences, preferential type II and type I CSA loss between limbs, respectively.

CONCLUSION

Of the limited available evidence, stroke appears to result in a shift to a higher proportion of type II muscle fibers in the paretic muscles. There are mixed results for effects on muscle fiber CSA, but there is some evidence of specific atrophy of type II muscle fibers.

IMPACT

Changes in paretic skeletal muscle fibers of individuals with stroke may explain, in part, the substantial losses in strength and power in this population. Interventions to restore type II muscle fiber size may benefit people with stroke.

The effect of a prior eccentric lowering phase on concentric neuromechanics during multiple joint resistance exercise in older adults

Aging involves a marked decline in physical function and especially muscle power. Thus, optimal resistance exercise (RE) to improve muscle power is required for exercise prescription. An eccentric lowering phase immediately before a concentric lift (ECC-CON) may augment concentric power production, due to various proposed mechanisms (e.g., elastic recoil, pre-activation, stretch reflex, contractile history), when compared with a concentric contraction alone (CON-Only). This study compared the effect of a prior eccentric lowering phase on older adult concentric power performance (ECC-CON vs. CON-Only) during a common multiple joint isoinertial RE (i.e., leg press) with a range of loads. Twelve healthy older adult males completed two measurement sessions, consisting of ECC-CON and CON-Only contractions, performed in a counterbalanced order using 20-80% of one repetition maximum [% 1RM] loads on an instrumented isoinertial leg press dynamometer that measured power, force, and velocity. Muscle activation was assessed with surface electromyography (sEMG). For mean power ECC-CON>CON-Only, with a pronounced effect of load on the augmentation of power by ECC-CON (+19 to +55%, 35-80% 1RM, all p < 0.032). Similarly, for mean velocity ECC-CON>CON-Only, especially as load increased (+15 to 54%, 20-80% 1RM, all p < 0.005), but mean force showed more modest benefits of ECC-CON (+9 to 14%, 50-80% 1RM, all p < 0.05). In contrast, peak power and velocity were similar for ECC-CON and CON-Only with all loads. Knee and hip extensor sEMG were similar for both types of contractions. In conclusion, ECC-CON contractions produced greater power, and velocity performance in older adults than CON-Only and may provide a superior stimulus for chronic power development.

Implementation and Core Components of a Multimodal Program including Exercise and Nutrition in Prevention and Treatment of Frailty in Community-Dwelling Older Adults: A Narrative Review

Increasing disability-free life expectancy is a crucial issue to optimize active ageing and to reduce the burden of evitable medical costs. One of the main challenges is to develop pragmatic and personalized prevention strategies in order to prevent frailty, counteract adverse outcomes such as falls and mobility disability, and to improve quality of life. Strong evidence reports the effectiveness of exercise interventions to improve various physical parameters and muscle function that are cornerstones of frailty. Other findings also suggest that the interactions between nutrition and physical exercise with or without health behavior promotion prevent the development of frailty. Multimodal programs, including structured exercise, adequate dietary intervention and health behavior promotion, appear increasingly consensual. However, in order for implementation in real-life settings, some pitfalls need to be addressed. In this perspective, structuring and tailoring feasible, acceptable and sustainable interventions to optimize exercise training responses are essential conditions to warrant short, medium and long-term individual benefits. The different components of exercise programs appear to be fairly consensual and effective. However, specific composition of the programs proposed (frequency, intensity, type, time, volume and progressiveness) have to be tailored to individual characteristics and objectives in order to improve exercise responses. The intervention approaches, behavioral strategies and indications for these programs also need to be refined and framed. The main objective of this work is to guide the actions of healthcare professionals and enable them to widely and effectively implement multimodal programs including exercise, nutrition and behavioral strategies in real-life settings.

Physical performance and maximum tongue pressure associated with oral intake independence: a retrospective study on hospitalized patients with heart failure

Dysphagia in patients with heart failure leads to poorer outcomes during hospitalization and after discharge. Therefore, addressing dysphagia is critical for improving patient prognosis. This retrospective observational study aimed to evaluate associations between improvements in swallowing dysfunction at the time of hospital discharge and the physical function, cognitive function, nutritional status, and maximum tongue pressure (MTP). Overall, 111 patients who underwent cardiac rehabilitation and were deemed to have oral intake impairment were included. The exclusion criteria comprised the following: pre-admission diagnosis of dysphagia, in-hospital death, and missing data. Patients were categorized based on whether they did (n = 65) or did not (n = 46) exhibit improvements in oral intake impairment, which were determined from the functional oral intake scale (FOIS) score at discharge. Associations between potential explanatory variables and the FOIS score at discharge were assessed using a linear regression model. After adjusting for covariates, such as age, sex, heart failure severity, short physical performance battery score, Mini-Mental State Examination score, transthyretin level, and provision of swallowing therapy, the FOIS score at discharge was significantly associated with the MTP (P = 0.024, confidence interval: 0.006-0.046). In conclusion, the MTP was independently associated with improvements in FOIS in patients with heart failure.

Association of muscle fiber composition with health and exercise-related traits in athletes and untrained subjects

Skeletal muscle is a heterogenous and metabolically active tissue, the composition of which is associated with multiple traits. The aim of the study was to determine whether there are additional health and exercise-related traits associated with muscle fiber composition in athletes and non-athletes. This study recruited 164 Russian participants (51 endurance and 48 power athletes; 65 controls). Vastus lateralis muscle fiber composition was assessed by immunohistochemistry. Slow-twitch muscle fiber percentage (STMF%) was significantly greater in endurance than power athletes and non-athletes, and in non-athlete females than males. STMF% was positively associated with athletes' training frequency, non-athletes' and endurance athletes' age, endurance athletes' competition level and chest depth, and power athletes' training age. STMF% was negatively associated with diastolic blood pressure in power athletes and with systolic blood pressure and reaction time in non-athletes. In all participants, STMF% was positively associated with age, tolerance to long distance exercise, chest depth and fracture incidence, and negatively with systolic blood pressure and resting heart rate. Age, sex and training frequency explained 10.6% and 13.2% of the variance in STMF% in endurance and power athletes, respectively. This is one of the most comprehensive studies involving athletes and untrained subjects and provides novel information concerning associations of increased STMF percentage with lower resting heart rate, better tolerance to long distances, faster reaction time and larger chest depth. On the other hand, the increased percentage of fast-twitch muscle fibers was associated with rare fracture incidence.

Potential Benefits of a Minimal Dose Eccentric Resistance Training Paradigm to Combat Sarcopenia and Age-Related Muscle and Physical Function Deficits in Older Adults

The ability of older adults to perform activities of daily living is often limited by the ability to generate high mechanical outputs. Therefore, assessing and developing maximal neuromuscular capacity is essential for determining age-related risk for functional decline as well as the effectiveness of therapeutic interventions. Interventions designed to enhance neuromuscular capacities underpinning maximal mechanical outputs could positively impact functional performance in daily life. Unfortunately, < 10% of older adults meet the current resistance training guidelines. It has recently been proposed that a more “minimal dose” RT model may help engage a greater proportion of older adults, so that they may realize the benefits of RT. Eccentric exercise offers some promising qualities for such an approach due to its efficiency in overloading contractions that can induce substantial neuromuscular adaptations. When used in a minimal dose RT paradigm, eccentric-based RT may be a particularly promising approach for older adults that can efficiently improve muscle mass, strength, and functional performance. One approach that may lead to improved neuromuscular function capacities and overall health is through heightened exercise tolerance which would favor greater exercise participation in older adult populations. Therefore, our perspective article will discuss the implications of using a minimal dose, submaximal (i.e., low intensity) multi-joint eccentric resistance training paradigm as a potentially effective, and yet currently underutilized, means to efficiently improve neuromuscular capacities and function for older adults.

Assessment of Tongue Strength in Sarcopenia and Sarcopenic Dysphagia: A Systematic Review and Meta-Analysis

Sarcopenic dysphagia is defined as difficulty in swallowing due to sarcopenia, which may be related to weakness of the tongue muscles. This meta-analysis aimed to explore the association between tongue strength and sarcopenia and to determine whether tongue strength measurement could be a specific indicator of sarcopenic dysphagia. We conducted a systematic search of electronic databases from their inception to February 2021 for clinical studies that investigated tongue strength in participants with and without sarcopenia. The primary outcome was the weighted mean difference (WMD) and standardized mean difference (SMD) of tongue pressure between the different groups. The secondary outcome was the correlation of tongue pressure with the subcomponents that defined sarcopenia. Ten studies that involved 1,513 participants were included in the meta-analysis. Compared with those without sarcopenia, patients with sarcopenia had significantly less tongue pressure, with a WMD of -4.353 kPa (95% CI, -7.257 to -1.450) and an SMD of -0.581 (95% CI, -0.715 to -0.446). There was no significant difference in tongue pressure between patients with sarcopenic dysphagia and those with non-sarcopenic dysphagia, with a WMD of -1.262 kPa (95% CI, -8.442 to 5.918) and an SMD of -0.187 (95% CI, -1.059 to 0.686). Significant positive associations were identified between tongue pressure and grip strength and between tongue pressure and gait speed, with correlation coefficients of 0.396 (95% CI, 0.191 to 0.567) and 0.269 (95% CI, 0.015 to 0.490), respectively. Reduced tongue strength is associated with sarcopenia but is not an exclusive marker for sarcopenic dysphagia. Tongue strength correlates with the values of subcomponents that define sarcopenia. In patients with low performance of sarcopenia subcomponent, tongue pressure must be examined to diagnose subclinical dysphagia. Protocol registration: This meta-analysis was registered on INPLASY (registration number INPLASY202120060).

Utilisation of Post-Activation Performance Enhancement in Elderly Adults

With age, many physiological changes occur in the human body, leading to a decline in biological functions, and those related to the locomotor system are some of the most visible. Hence, there is a particular need to provide simple and safe exercises for the comprehensive development of physical fitness among elderly adults. The latest recommendations for the elderly suggest that the main goal of training should be to increase muscle power. The post-activation performance enhancement effect underpinning complex training might be an approach that will allow for the development of both muscle strength and velocity of movement, which will result in an increase in muscle power and improve the ability to perform daily activities and decrease injury risk. This article briefly introduces a complex training model adapted to the elderly with its potential benefits and proposes a direction for further studies.

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 eccentric mechanotransduction, neuro-muscular transmission, and structural reversibility of muscle fatty infiltration. An experimental advanced disuse muscle-wasting model of rabbit supraspinatus

INTRODUCTION

Full-thickness rotator cuff tear is present in almost 50% of patients over age 65 years, and its degree is known to be a good predictor of the severity of muscle-wasting (MW) sarcopaenia, also known as fatty degeneration (FD). A FD CT grade > 2° is recognized as a borderline of its reversibility. A disuse model of supraspinatus FD (grade 2) in rabbits provides clinically relevant data. Therefore, the present study evaluates the correlation between eccentric mechanotransduction, neuromuscular transmission (NT), and reversibility of muscle fatty infiltration (MFI) in rabbit supraspinatus FD > 2°.

MATERIAL AND METHODS

The supraspinatus tendon was detached from the greater tubercle, infraspinatus, and subscapularis in 16 rabbits. The tendon was reinserted after 12 weeks, and the animals were euthanized 24 weeks after reconstruction. MFI was measured in the middle part of the supraspinatus. Single-fibre EMG (SFEMG) examination of the supraspinatus NT was performed on 4 animals.

RESULTS

The power of analysis was 99%. Significant differences in MFI volume were found between the operated (4.6 ±1.1%) and the opposite control sides (2.91 ±0.61%) (p < 0.001). SFEMG revealed no significant differences between the disuse and the control supraspinatus muscles (p > 0.05); however, 6.5% of the examined muscle fibres exhibited NT disorders combined with blockade of conduction in 2.5% of muscle fibres.

CONCLUSIONS

Critical MFI in a disuse model of rabbit supraspinatus FD, CT grade > 2°, is substantially reversible by eccentric training despite subclinical impairment of neuromuscular transmission. In addition, 0.63% reversal of MFI is correlated with 1% hypertrophy of type I and II muscle fibre diameter.

Age Related Changes in Motor Function (II). Decline in Motor Performance Outcomes

Age-related impairments in motor performance are caused by a deterioration in mechanical and neuromuscular functions, which have been investigated from the macro-level of muscle-tendon unit to the micro-level of the single muscle fiber. When compared to the healthy young skeletal muscle, aged skeletal muscle is: (1) weaker, slower and less powerful during the performance of voluntary contractions; (2) less steady during the performance of isometric contractions, particularly at low levels of force; and (3) less susceptible to fatigue during the performance of sustained isometric contractions, but more susceptible to fatigue during the performance of high-velocity dynamic contractions. These impairments have been discussed to be mainly the result of: a) loss of muscle mass and selective atrophy of type II muscle fibers; b) altered tendon mechanical properties (decreased tendon stiffness); c) reduced number and altered function of motor units; d) slower muscle fiber shortening velocity; e) increased oscillation in common synaptic input to motor neurons; and f) altered properties and activity of sarcoplasmic reticulum. In this second part of a two-part review we have detailed the age-related impairments in motor performance with a reference to the most important mechanical and neuromuscular contributing factors.

Effects of age on vertical jump performance and muscle morphology characteristics in females

BACKGROUND

Declines in muscle morphology and function are commonly reported as a consequence of aging. However, few studies have investigated the influence of age on a comprehensive set of muscle function-related measures (i.e., reactive strength, power, etc.) that focuses on a dynamic performance task such as the vertical jump across the adult life span. This study aimed to examine the effects of age on muscle morphology characteristics (muscle cross-sectional area [CSA] and echo intensity [EI]) and vertical jump height, power, and reactive strength index (RSI) in females.

METHODS

Twenty-six young (22±2 years), 30 middle-aged (36±5 years), and 23 older (71±5 years) females participated in this study. Muscle CSA and EI were determined from ultrasound scans of the vastus lateralis. Countermovement jumps were used to assess jump height, RSI, movement time, and peak power (Pmax).

RESULTS

Muscle CSA, jump height, and Pmax were higher for the young compared to the old and middle-aged (P≤0.027) and for the middle-aged compared to the old (P<0.001). Movement time and EI values were lower (P≤0.004) and RSI values were higher (P<0.001) for the young and middle-aged compared to the old; however, no differences were observed between the young and middle-aged (P=0.367-0.620).

CONCLUSIONS

Of all the variables assessed in this study, RSI exhibited the greatest decline (76%) between the young and old females. Such findings highlight the importance of reactive strength when assessing age-related changes in neuromuscular performance.

Increase of resting muscle stiffness, a less considered component of age-related skeletal muscle impairment

Elderly people perform more slowly movements of everyday life as rising from a chair, walking, and climbing stairs. This is in the first place due to the loss of muscle contractile force which is even more pronounced than  the loss of muscle mass. In addition, a secondary, but not negligible, component is the rigidity or increased stiffness which requires greater effort to produce the same movement and limits the range of motion of the joints. In this short review, we discuss the possible determinants of the limitations of joint mobility in healthy elderly, starting with the age-dependent alterations of the articular structure and focusing on the increased stiffness of the skeletal muscles. Thereafter, the possible mechanisms of the increased stiffness of the muscle-tendon complex are considered, among them changes in the muscle fibers, alterations of the connective components (extracellular matrix or ECM, aponeurosis, fascia and tendon) and remodeling of the neural pattern of muscle activation with increased of antagonist co-activation.

Increase of resting muscle stiffness, a less considered component of age-related skeletal muscle impairment

Elderly people perform more slowly movements of everyday life as rising from a chair, walking, and climbing stairs. This is in the first place due to the loss of muscle contractile force which is even more pronounced than the loss of muscle mass. In addition, a secondary, but not negligible, component is the rigidity or increased stiffness which requires greater effort to produce the same movement and limits the range of motion of the joints. In this short review, we discuss the possible determinants of the limitations of joint mobility in healthy elderly, starting with the age-dependent alterations of the articular structure and focusing on the increased stiffness of the skeletal muscles. Thereafter, the possible mechanisms of the increased stiffness of the muscle-tendon complex are considered, among them changes in the muscle fibers, alterations of the connective tissue components, i.e., extracellular matrix (ECM), aponeurosis, tendon and fascia, and remodeling of the neural pattern of muscle activation that increases antagonist co-activation.

Comparisons of Knee Extensor Functional Demand During Gait by Age, Physical Activity Level, and the Impact of Acute Exercise and Walking Speed

The link between age-related changes in muscle strength and gait is unclear. We tested if knee extensor functional demand differs by age and physical activity status and if functional demand increases with walking speed or after exercise. Gait and knee extensor muscle torque were collected from young adults and highly and less active older adults before and after treadmill walking. Functional demand was the ratio of knee moments during gait to knee extensor muscle torques estimated from participant-specific torque-velocity curves. Functional demand at the peak knee flexion moment was greater in less active older adults than young adults (29.3% [14.3%] vs 24.6% [12.1%]) and increased with walking speed (32.0% [13.9%] vs 22.8% [10.4%]). Functional demand at both knee extension moments increased ∼2% to 3% after exercise. The low functional demand found in this study suggests that healthy adults maintain a reserve of knee extensor strength.

Advanced Age Redistributes Positive but Not Negative Leg Joint Work during Walking

Supplemental digital content is available in the text.

Introduction

Advanced age brings a distal-to-proximal redistribution of positive joint work during walking that is relevant to walking performance and economy. It is unclear whether negative joint work is similarly redistributed in old age. Negative work can affect positive work through elastic energy return in gait. We determined the effects of age, walking speed, and grade on positive and negative joint work in young and older adults.

Methods

Bilateral ground reaction force and marker data were collected from healthy young (age = 22.5 yr, n = 18) and older (age = 76.0 yr, n = 22) adults walking on a split-belt instrumented treadmill at 1.1, 1.4, and 1.7 m·s⁻¹ at each of three grades (0%, 10%, and −10%). Subjects also performed maximal voluntary eccentric, isometric, and concentric contractions for the knee extensors (120°·s⁻¹, 90°·s⁻¹, and 0°·s⁻¹) and plantarflexors (90°·s⁻¹, 30°·s⁻¹, and 0°·s⁻¹).

Results

Compared with young adults, older adults exhibited a distal-to-proximal redistribution of positive leg joint work during level (P < 0.001) and uphill (P < 0.001) walking, with larger differences at faster walking speeds. However, the distribution of negative joint work was unaffected by age during level (P = 0.150) and downhill (P = 0.350) walking. Finally, the age-related loss of maximal voluntary knee extensor (P < 0.001) and plantarflexor (P = 0.001) strength was smaller during an eccentric contraction versus concentric contraction for the knee extensors (P < 0.001) but not for the plantarflexors (P = 0.320).

Conclusion

The distal-to-proximal redistribution of positive joint work during level and uphill walking is absent for negative joint work during level and downhill walking. Exercise prescription should focus on improving ankle muscle function while preserving knee muscle function in older adults trying to maintain their independence.

Effect of eccentric-based rehabilitation on hand tremor intensity in Parkinson disease

BACKGROUND AND PURPOSE

Hand tremor is a disturbing yet sometimes resistant symptom in persons with Parkinson disease (PD). Although many exercise regimens for these people have gained attention in recent years, the effect of resistance training and especially eccentric training on parkinsonian tremor is still uncertain. This study was conducted to investigate the precise effect of upper limb eccentric training on hand tremor in PD.

METHODS

In this randomized controlled trial, a consecutive sample of 21 persons with PD recruited from general hospitals went through 6 weeks of upper limb pure eccentric training as the intervention group (n = 11) or no additional exercise during this period as the control group (n = 10). Resting and postural tremor amplitudes were measured with the cellphone-based accelerometer.

RESULTS

Comparing hand tremor amplitudes before and after the trial showed a significant reduction in resting tremor amplitude in the intervention group after exercise sessions (p < 0.05) while detecting no changes in the control group during 6 weeks of study. Meanwhile, postural tremor amplitude remained unchanged in both groups.

Relevance to assess and preserve muscle strength in aging field

According to the revised European consensus on sarcopenia, muscle strength is the primary parameter of sarcopenia and is associated with adverse outcomes or physical limitation. This literature review aims to clarify how and why to measure and preserve muscle strength in older population. Overall, the relationship between muscle strength and physical function is impacted by level of muscle mass, the degree of obesity (BMI), age and physical activity. Therefore, these factors are to be considered in the evaluation of muscle strength. It is necessary to have objective, reliable and sensitive tools to assess muscle strength, in different populations to detect and quantify weakness, to adapt physical exercises to patients' capacity and to evaluate the effects of treatment. Handgrip strength measurement might be reasonable for clinical practice while the measurement of knee flexors/extensors strength with both 1RM and dynamometers is increasingly important yet restricted by the requirement of special equipment. Physical activity and nutrition are two important behavioral factors to maintain muscle strength. Combined exercise and nutrition interventions improved muscle strength to a more prominent degree than exercise or nutrition alone.

Functions of estrogen and estrogen receptor signaling on skeletal muscle

Activity of estrogen, a sex steroid hormone, is not only limited to the reproductive organs but also involves other organs and tissues, including skeletal muscle. In postmenopausal women, estrogen decline causes endocrine and metabolic dysfunction, leading to a predisposition to osteoporosis, metabolic syndrome, and decreased muscle mass and strength. The decline in skeletal muscle mass often associates with sarcopenia, a popular condition observed in fragile elder people. In addition, varying estrogen levels associated with the menstrual phases may modulate exercise performance in women. Estrogen is thus considered to play a crucial role in skeletal muscle homeostasis and exercise capacity, although its precise mechanisms remain to be elucidated. In this article, we review the role of estrogen in the skeletal muscle, outlining the proposed molecular mechanisms. We especially focus on the current understanding of estrogen actions on mitochondria metabolism in skeletal muscle.

Physical activity and age-related biomechanical risk factors for knee osteoarthritis

BACKGROUND

Knee osteoarthritis (OA) is a highly prevalent disease leading to mobility disability in the aged that could, in part, be initiated by age-related alterations in knee mechanics. However, if and how knee mechanics change with age remains unclear.

RESEARCH QUESTION

What are the impacts of age and physical activity (PA) on biomechanical characteristics that can affect the loading environment in the knee during gait?

METHODS

Three groups (n = 20 each, 10 male and 10 female) of healthy adults were recruited: young (Y, 21-35 years), mid-life highly active (MHi, 55-70 years, runners), and mid-life less active (MLo, 55-70 years, low PA). Outcome measures included knee kinematics and kinetics and co-activation during gait, and knee extensor muscle torque and power collected at baseline and after a 30-minute treadmill trial to determine the impact of prolonged walking on knee function.

RESULTS

At baseline, high-velocity concentric knee extensor power was lower for MLo and MHi compared with Y, and MLo displayed greater early (6.0 ± 5.8 mm) and peak during stance (11.3 ± 7.8 mm) femoral anterior displacement relative to the tibia compared with Y (0.2 ± 5.6 and 4.4 ± 6.8 mm). Also at baseline, MLo showed equal quadriceps:hamstrings activation, while Y showed greater relative hamstrings activation during midstance. The walking bout induced substantial knee extensor fatigue (decrease in maximal torque and power) in Y and MLo, while MHi were fatigue-resistant.

SIGNIFICANCE

These results indicate that maintenance of PA in mid-life may impart small but measurable effects on knee function and biomechanics that may translate to a more stable loading environment in the knee through mid-life and thus could reduce knee OA risk long-term.

Muscle Fatigue Does Not Change the Effects on Lower Limbs Strength Caused by Aging and Parkinson's Disease

The aim of this study was to determine the impact of aging and Parkinson’s disease (PD) on lower limb muscle strength before and after muscle fatigue. One hundred thirty-five individuals were distributed over seven groups according to their age (20, 30, 40, 50, 60, 70 years old) and disease. Participants performed maximum voluntary isometric contractions (MVIC) in a leg press device followed by the muscle fatigue protocol (repeated sit-to-stand task). Immediately after muscle fatigue (less than 2 min), the MVIC were repeated. The peak force, peak rate of force development (first 50, 100, 200 ms), and root mean square and peak values of the vastus lateralis and vastus medialis muscle activity during MVIC were calculated before and after muscle fatigue. We found more pronounced reductions in lower limb muscle strength parameters (lower limb force, RFD-100 and RFD-200 - p<0.05) in individuals over 50 years of age and with PD. In addition, there was an inverse relation between aging and lower limb muscle strength parameters. The main findings were the lack of changes in peak force, RFDs and muscle activity of the vastus lateralis and vastus medialis after muscle fatigue according to aging and PD, and similar lower limb muscle strength parameters (before and after muscle fatigue) and effect of muscle fatigue in PD compared to the aged groups (60 and 70 years old groups).

Effects of age and sex on shoulder biomechanics and relative effort during functional tasks

Age-related decline in muscle strength can compromise shoulder function, which could increase the effort needed to perform activities of daily living (ADLs). The purpose of this cross-sectional study was to determine for the first time the relative shoulder effort during ADLs in healthy young and older adults. Ten healthy young adults and ten healthy older adults were tested for maximal isokinetic torque and on a set of ADL tasks. Using inverse dynamics, the shoulder torques during ADLs were referenced to the maximal isokinetic torque and relative effort was determined. Older compared to younger adults had >40% lower isokinetic shoulder abduction strength. The ratio of peak joint torque during six ADLs over the maximal isokinetic torque, i.e., relative effort, was higher in old (∼52%) compared with young adults (∼22%, p < 0.05). Relative effort in older adults was over 40% in overhead activities and particularly high in abduction and reaching tasks, over 60%. Healthy older compared with younger adults perform most ADL tasks involving the shoulder joint with nearly twice the level of relative effort. The concomitant reductions in maximal shoulder isokinetic torque and increases in relative effort may be related to the high prevalence of musculoskeletal pain and shoulder dysfunction in old age reported in epidemiological studies.

Impact of Aging on Endurance and Neuromuscular Physical Performance: The Role of Vascular Senescence

The portion of society aged ≥60 years is the fastest growing population in the Western hemisphere. Aging is associated with numerous changes to systemic physiology that affect physical function and performance. We present a narrative review of the literature aimed at discussing the age-related changes in various metrics of physical performance (exercise economy, anaerobic threshold, peak oxygen uptake, muscle strength, and power). It also explores aging exercise physiology as it relates to global physical performance. Finally, this review examines the vascular contributions to aging exercise physiology. Numerous studies have shown that older adults exhibit substantial reductions in physical performance. The process of decline in endurance capacity is particularly insidious over the age of 60 years and varies considerably as a function of sex, task specificity, and individual training status. Starting at the age of 50 years, aging also implicates an impressive deterioration of neuromuscular function, affecting muscle strength and power. Muscle atrophy, together with minor deficits in the structure and function of the nervous system and/or impairments in intrinsic muscle quality, plays an important role in the development of neuromotor senescence. Large artery stiffness increases as a function of age, thus triggering subsequent changes in pulsatile hemodynamics and systemic endothelial dysfunction. For this reason, we propose that vascular senescence has a negative impact on cerebral, cardiac, and neuromuscular structure and function, detrimentally affecting physical performance.

Age-related differences in muscle activity patterns during walking in healthy individuals

OBJECTIVE

To examine how muscle activity over the entire gait cycle changes with increasing age.

METHODS

Electromyography data of the erector spinae, rectus femoris, vastus lateralis, biceps femoris, tibialis anterior and gastrocnemius muscles were collected by an instrumented gait analysis during over ground walking in healthy adults aged between 20 and 89 years. Participants were categorized per decade (n = 105, 15 per decade, decades 3-9). Normalized integrated linear envelopes of the electromyographic signal were calculated for one stride. A one way ANOVA using spm1d statistics explored the differences between age groups, followed by a post hoc analysis.

RESULTS

While initiation of decline commenced at the age of 60 for erector spinae and tibialis anterior, age-related changes are most pronounced after the age of 80. Concerning timing of muscle activity, subjects in decade 7-9 had prolonged activity and/or early activity of the erector spinae, vastus lateralis, biceps femoris, tibialis anterior and gastrocnemius compared to other decades. Regarding amplitude of muscle activity, decreased peak amplitudes of the erector spinae, rectus femoris, vastus lateralis and gastrocnemius were observed in decades 7-9 compared to other decades.

CONCLUSION

Both timing and amplitude of muscle activation patterns need to be considered to understand the aging process. Regarding the erector spinae, tibialis anterior and vastus lateralis, a decrease in muscle activation coincides with prolonged activity, compared to the gastrocnemius where decreased muscle activation is associated with early activation.

Age-induced changes in the lower limb muscle activities during uphill walking at steep grades

BACKGROUND

Uphill walking is particularly challenging for elderly persons. However, there is a lack of age-differentiated studies investigating the underlying differences in muscle activation when walking on sloped surfaces. These studies are needed, e.g., for planning of evacuations of large modern cruise ships with long walking distances on often inclined surfaces.

METHODS

An age-differentiated, gender-balanced study with 26 young (20-30 years) and 26 elderly people (60-77 years) was therefore conducted, investigating uphill walking at 7° and at 14° contrasted to level walking on a treadmill. EMG signals of musculus gluteus maximus (GMAX), m. biceps femoris (BF), m. rectus femoris (RF), m. vastus medialis (VM), m. gastrocnemius medialis (GAS) and m. soleus (SOL) were analysed with regard to mean and maximum muscle activities and timing during the gait cycle.

RESULTS

The results showed that walking uphill at 14° was highly strainful for elderly people. In line with previous research, young people mostly "pushed" themselves uphill with the GAS and SOL. In contrast, elderly people not only used the known compensatory ability of hip muscles to propel the trailing leg, but also showed a high level of BF activation prolonged until the mid-stance phase at the steepest uphill gradient of 14°.

SIGNIFICANCE

The strikingly long activation of the BF until the mid-stance phase in elderly people at steep gradients is an unexpected, new finding. It suggests that, instead of pushing, elderly people "pull" themselves uphill. In cases of evacuations, the lower physical fitness levels of elderly passengers and their increased need for assistance on inclined surfaces have to be planned for in advance. Considering the findings in (home) training programmes might help elderly people to strengthen lower limb muscles and to enhance the efficiency of muscle activation patterns enabling them to manage steep inclinations more easily.

Influence of working memory and executive function on stair ascent and descent in young and older adults

This study assessed the influence of attention division, working memory and executive function on stair ascent and descent in young and older adults. Twenty young (25.5 ± 2.1 yrs) and 20 older adults (68.4 ± 5.4 yrs) ascended and descended a 3-step staircase with no simultaneous cognitive task (single-motor task) or while performing a cognitive task (dual-task condition). The cognitive task involved either 1) recalling a word list of the subject's word-span minus 2 words (SPAN-2) to assess the attention division effect, 2) a word list of subject's word-span (SPAN-O) to assess the working memory effect, or 3) recalling in alphabetical order, a word list of the subject's word-span (SPAN-A) to assess the executive function effect. Word-span corresponds to the longest string of words that can be recalled correctly. The duration of ascent and descent of stairs was used to assess the cognitive-motor interaction. Stair ascent and descent duration did not differ between age groups for the single-motor task, and was similar between single-motor task and SPAN-2 in both groups (p > 0.05). In contrast, stair ascent and descent duration increased with SPAN-O compared with SPAN-2 for both groups (p < 0.01). Stair ascent (p = 0.017) and descent (p = 0.008) were longer in SPAN-A than SPAN-O only in older adults. Healthy aging was not associated with a decrease in the capacity to perform motor-cognitive dual tasks that involved ascending and descending of stairs when the cognitive task only required working memory. However, the decrease in dual-task performance involving executive functioning may reflect a subclinical cognitive decline in healthy older adults.

Biomechanical and physiological age differences in a simulated forward fall on outstretched hands in women

BACKGROUND

Falling on the outstretched hands, a protective mechanism to arrest the body and avoid injury, requires upper limb and trunk motor control for effective body descent. Older women are particularly susceptible to injury from a forward fall, but the biomechanical and physiological (e.g., muscle strength) factors related to this increased risk are poorly understood. Determining age differences in the modifiable neuromuscular factors related to a forward fall landing and descent could help to inform injury prevention strategies. The purpose was to investigate age related differences in upper extremity strength and fall arrest strategy differences during a simulated fall and to evaluate the relationships between muscle strength and biomechanical variables.

METHODS

Nineteen younger (mean age 23.0 yrs., SD 3.8) and 16 older (mean age 68.2 yrs., SD 5.3) women performed five trials of simulated falls. Biomechanical measures and electromyographic muscle activity were recorded during the descents. Concentric, isometric and eccentric strength of the non-dominant upper limb was measured via a dynamometer using a customized protocol.

FINDINGS

Older women demonstrated lower concentric elbow extension strength compared to younger women (p = 0.002). Landing strategies differed where younger women had significantly greater elbow joint angle (p = 0.006) and velocity (p = 0.02) at impact. Older women demonstrated diminished capacity to absorb energy and control descent on outstretched hands compared to younger women (p = 0.001).

INTERPRETATION

The landing strategy used by older women along with decreased energy absorption may increase risk of fall-related injury and increase the likelihood of trunk or head impact with the ground.

Voluntary activation and variability during maximal dynamic contractions with aging

Whether reduced supraspinal activation contributes to age-related reductions in maximal torque during dynamic contractions is not known. The purpose was to determine whether there are age differences in voluntary activation and its variability when assessed with stimulation at the motor cortex and the muscle during maximal isometric, concentric, and eccentric contractions. Thirty young (23.6 ± 4.1 years) and 31 old (69.0 ± 5.2 years) adults performed maximal isometric, shortening (concentric) and lengthening (eccentric) contractions with the elbow flexor muscles. Maximal isometric contractions were performed at 90° elbow flexion and dynamic contractions at a velocity of 60°/s. Voluntary activation was assessed by superimposing an evoked contraction with transcranial magnetic stimulation (TMS) or with electrical stimulation over the muscle during maximal voluntary contractions (MVCs). Old adults had lower MVC torque during isometric (- 17.9%), concentric (- 19.7%), and eccentric (- 9.9%) contractions than young adults, with less of an age difference for eccentric contractions. Voluntary activation was similar between the three contraction types when assessed with TMS and electrical stimulation, with no age group differences. Old adults, however, were more variable in voluntary activation than young (standard deviation 0.99 ± 0.47% vs. 0.73 ± 0.43%, respectively) to both the motor cortex and muscle, and had greater coactivation of the antagonist muscles during dynamic contractions. Thus, the average voluntary activation to the motor cortex and muscle did not differ with aging; however, supraspinal activation was more variable during maximal dynamic and isometric contractions in the old adults. Lower predictability of voluntary activation may indicate subclinical changes in the central nervous system with advanced aging.

Age-related differences in the motor unit action potential size in relation to recruitment threshold

Motor unit action potential size (MUAP_size ) versus recruitment threshold (RT) relationship analysis provides a non-invasive measure of motor unit (MU) hypertrophy; however, this method's ability to identify MU atrophy is unknown. This investigation sought to determine if MUAP_size versus RT relationship slope (AP_slope ) comparison could identify evidence of MU atrophy in older individuals. Surface electromyography signals were recorded from the first dorsal interosseous (FDI) of fourteen young (YG, age = 22·29 ± 2·79 years) and ten older (OG, 61·0 ± 2·0 years) subjects during a 50% maximal voluntary contraction (MVC) isometric trapezoidal muscle action. The signals were decomposed to yield a MUAP_size and RT for each MU. For each subject, the MUs recruited between 10% and 50% MVC were linearly regressed as a function of RT to calculate an individual AP_slope . FDI cross-sectional area (CSA) and echo intensity (EI) were quantified via ultrasonography. The mean AP_slope was lower for OG (0·033 ± 0·010 mV %MVC^-1 ) than YG (0·056 ± 0·019 mV %MVC^-1 ). OG and YG possessed similar CSAs (OG: 2·09 ± 0·31 cm² ; YG: 2·08 ± 0·41 cm² ); however, OG (53·25 ± 7·56 AU) had greater EI than YG (43·87 ± 7·59 AU). The lower OG mean AP_slope was due to smaller MUAP_sizes of higher-threshold MUs, likely due to atrophy of muscle fibres that comprise those MUs. In support, similar CSA with greater EI indicated increased adipose and fibrous tissue and reduced contractile tissue in OG. Thus, MUAP_size versus RT relationship may provide a non-invasive measure of MU atrophy.

Female Age-Related Differences in Biomechanics and Muscle Activity During Descents on the Outstretched Arms

The purposes of this study were to examine female age differences in: (1) upper extremity (UE) and trunk muscle activity, elbow joint moment, loading force, and UE energy absorption during a controlled forward body descent; and (2) UE muscle strength. Twenty young (mean 24.8 ± 3.4 years) and 20 older (68.4 ± 5.7 years) women were assessed via dynamometry for isometric, concentric, and eccentric UE strength and performed forward descents on force plates at three body lean angles (60°, 45°, and 30° from horizontal). Significant differences (p < .05) were found for muscle strength, biomechanics, and muscle activity. Concentric UE strength averaged 15% lower in older women. At 30° body lean, older women absorbed less energy. Older women had greater biceps brachii activation and less external oblique activation at all body lean angles. Age differences in muscle strength, activation, and energy absorption may contribute to fall-related injury risk.

Effectiveness of a Home-Based Eccentric-Exercise Program on the Torque-Angle Relationship of the Shoulder External Rotators: A Pilot Study

CONTEXT

The role of the rotator cuff is to provide dynamic stability to the glenohumeral joint. Human and animal studies have identified sarcomerogenesis as an outcome of eccentric training indicated by more torque generation with the muscle in a lengthened position.

OBJECTIVE

The authors hypothesized that a home-based eccentric-exercise program could increase the shoulder external rotators' eccentric strength at terminal internal rotation (IR).

DESIGN

Prospective case series.

SETTING

Clinical laboratory and home exercising.

PARTICIPANTS

10 healthy subjects (age 30 ± 10 y).

INTERVENTION

All participants performed 2 eccentric exercises targeting the posterior shoulder for 6 wk using a home-based intervention program using side-lying external rotation (ER) and horizontal abduction.

MAIN OUTCOME MEASURES

Dynamic eccentric shoulder strength measured at 60°/s through a 100° arc divided into 4 equal 25° arcs (ER 50-25°, ER 25-0°, IR 0-25°, IR 25-50°) to measure angular impulse to represent the work performed. In addition, isometric shoulder ER was measured at 5 points throughout the arc of motion (45° IR, 30° IR, 15° IR, 0°, and 15° ER). Comparison of isometric and dynamic strength from pre- to posttesting was evaluated with a repeated-measure ANOVA using time and arc or positions as within factors.

RESULTS

The isometric force measures revealed no significant differences between the 5 positions (P = .56). Analysis of the dynamic eccentric data revealed a significant difference between arcs (P = .02). The percentage-change score of the arc of IR 25-50° was found to be significantly greater than that of the arc of IR 0-25° (P = .007).

CONCLUSION

After eccentric training the only arc of motion that had a positive improvement in the capacity to absorb eccentric loads was the arc of motion that represented eccentric contractions at the longest muscle length.

Age-related differences in muscle co-activation during locomotion and their relationship with gait speed: a pilot study

Background

Muscle co-activation plays an important role in enhancing joint stability for movement regulation during motor learning activities. In normal aging, greater muscle co-activation is induced during gait in elderly adults. This study investigated age-related changes in muscle co-activation and spatio-temporal parameters during gait and identified the relationship between muscle co-activation and gait speed.

Methods

A total of 46 adult volunteers participated in this study in three age groups (15 young adults [8 males, 7 females; age, 24.27 ± 2.71], 15 middle-aged adults [8 males, 7 females; age, 53.71 ± 2.52], and 16 elderly adults [7 males, 9 females; age, 76.88 ± 3.48]). All participants underwent locomotion analysis using a Three-dimensional motion analysis system and 12-channel dynamic electromyography.

Results

The elderly adults showed significantly higher co-activation than the young and middle-aged adults during gait (p < 0.05). In contrast, elderly adults showed significantly lower trunk co-activation than the young and middle-aged adults (p < 0.05). Muscle co-activation was significantly correlated with gait speed by aging. Muscle co-activation of the trunk showed a significant positive correlation with gait speed based on age. However, muscle co-activation of the lower extremity showed a significant negative correlation with gait speed based on age.

Conclusion

This finding demonstrated that less muscle co-activation of the trunk was related to locomotive instability in elderly adults. Therefore, clarification of the relationship between trunk co-activation and locomotor instability will be helpful for developing optimal rehabilitation of elderly people to prevent fall.

Prediction of In Vivo Knee Joint Loads Using a Global Probabilistic Analysis

Musculoskeletal models are powerful tools that allow biomechanical investigations and predictions of muscle forces not accessible with experiments. A core challenge modelers must confront is validation. Measurements of muscle activity and joint loading are used for qualitative and indirect validation of muscle force predictions. Subject-specific models have reached high levels of complexity and can predict contact loads with surprising accuracy. However, every deterministic musculoskeletal model contains an intrinsic uncertainty due to the high number of parameters not identifiable in vivo. The objective of this work is to test the impact of intrinsic uncertainty in a scaled-generic model on estimates of muscle and joint loads. Uncertainties in marker placement, limb coronal alignment, body segment parameters, Hill-type muscle parameters, and muscle geometry were modeled with a global probabilistic approach (multiple uncertainties included in a single analysis). 5-95% confidence bounds and input/output sensitivities of predicted knee compressive loads and varus/valgus contact moments were estimated for a gait activity of three subjects with telemetric knee implants from the "Grand Challenge Competition." Compressive load predicted for the three subjects showed confidence bounds of 333 ± 248 N, 408 ± 333 N, and 379 ± 244 N when all the sources of uncertainty were included. The measured loads lay inside the predicted 5-95% confidence bounds for 77%, 83%, and 76% of the stance phase. Muscle maximum isometric force, muscle geometry, and marker placement uncertainty most impacted the joint load results. This study demonstrated that identification of these parameters is crucial when subject-specific models are developed.

Functional Relevance of Relative Maintenance of Maximal Eccentric Quadriceps Torque in Healthy Old Adults

BACKGROUND

Old referenced to young adults show a relative maintenance of maximal eccentric (RELM) compared to concentric muscle torque: ∼76 and ∼59%, respectively. However, it is unknown if RELM affords functional benefits in old adults.

OBJECTIVE

We examined if there is specificity between the two types of peak quadriceps torque (i.e., concentric and eccentric) and timed gait performance measured during level, ramp, and stair walking and if gait performance was higher in old adults with high versus low RELM.

METHODS

We measured peak concentric and eccentric quadriceps torque at 60 and 120°/s and timed gait at habitual and safe-fast speeds in healthy young (age 22.7 years, n = 24) and old (age 70.0 years, n = 21) adults.

RESULTS

Comparable to previous studies, RELM was 21%, but instead of the anticipated specificity, we found that concentric compared with eccentric torque was more strongly associated with gait performance than eccentric torque, independently of walking direction and age (R2 = 0.16: eccentric vs. descending gaits; R2 = 0.17: eccentric vs. ascending gaits; R2 = 0.45: concentric vs. descending gaits; R2 = 0.56: concentric vs. ascending gaits, n = 45, all p < 0.01). Furthermore, old adults (n = 10) with ∼30% greater than normal levels of RELM (n = 11) ambulated at similar velocities measured on level and inclined surfaces.

CONCLUSION

Normal and 30% above normal levels of RELM do not seem to increase or predict healthy old adults' gait performance on level and inclined surfaces. Future work should examine if RELM is associated with a heightened performance in other measures of neuromuscular function, such as gait biomechanics, muscle activation, as well as rate and control of voluntary force development in old adults with high or low mobility.

Modeling age-related changes in muscle-tendon dynamics during cyclical contractions in the rat gastrocnemius

Efficient muscle-tendon performance during cyclical tasks is dependent on both active and passive mechanical tissue properties. Here we examine whether age-related changes in the properties of muscle-tendon units (MTUs) compromise their ability to do work and utilize elastic energy storage. We empirically quantified passive and active properties of the medial gastrocnemius muscle and material properties of the Achilles tendon in young (∼6 mo) and old (∼32 mo) rats. We then used these properties in computer simulations of a Hill-type muscle model operating in series with a Hookean spring. The modeled MTU was driven through sinusoidal length changes and activated at a phase that optimized muscle-tendon tuning to assess the relative contributions of active and passive elements to the force and work in each cycle. In physiologically realistic simulations where young and old MTUs started at similar passive forces and developed similar active forces, the capacity of old MTUs to store elastic energy and produce positive work was compromised. These results suggest that the observed increase in the metabolic cost of locomotion with aging may be in part due to the recruitment of additional muscles to compensate for the reduced work at the primary MTU. Furthermore, the age-related increases in passive stiffness coupled with a reduced active force capacity in the muscle can lead to shifts in the force-length and force-velocity operating range that may significantly impact mechanical and metabolic performance. Our study emphasizes the importance of the interplay between muscle and tendon mechanical properties in shaping MTU performance during cyclical contractions.

Analysis of concentric and eccentric contractions in biceps brachii muscles using surface electromyography signals and multifractal analysis

Muscle contractions can be categorized into isometric, isotonic (concentric and eccentric) and isokinetic contractions. The eccentric contractions are very effective for promoting muscle hypertrophy and produce larger forces when compared to the concentric or isometric contractions. Surface electromyography signals are widely used for analyzing muscle activities. These signals are nonstationary, nonlinear and exhibit self-similar multifractal behavior. The research on surface electromyography signals using multifractal analysis is not well established for concentric and eccentric contractions. In this study, an attempt has been made to analyze the concentric and eccentric contractions associated with biceps brachii muscles using surface electromyography signals and multifractal detrended moving average algorithm. Surface electromyography signals were recorded from 20 healthy individuals while performing a single curl exercise. The preprocessed signals were divided into concentric and eccentric cycles and in turn divided into phases based on range of motion: lower (0°–90°) and upper (>90°). The segments of surface electromyography signal were subjected to multifractal detrended moving average algorithm, and multifractal features such as strength of multifractality, peak exponent value, maximum exponent and exponent index were extracted in addition to conventional linear features such as root mean square and median frequency. The results show that surface electromyography signals exhibit multifractal behavior in both concentric and eccentric cycles. The mean strength of multifractality increased by 15% in eccentric contraction compared to concentric contraction. The lowest and highest exponent index values are observed in the upper concentric and lower eccentric contractions, respectively. The multifractal features are observed to be helpful in differentiating surface electromyography signals along the range of motion as compared to root mean square and median frequency. It appears that these multifractal features extracted from the concentric and eccentric contractions can be useful in the assessment of surface electromyography signals in sports medicine and training and also in rehabilitation programs.

Predictive and Reactive Locomotor Adaptability in Healthy Elderly: A Systematic Review and Meta-Analysis

Background

Locomotor adaptability is based on the implementation of error-feedback information from previous perturbations to predictively adapt to expected perturbations (feedforward) and to facilitate reactive responses in recurring unexpected perturbations (‘savings’). The effect of aging on predictive and reactive adaptability is yet unclear. However, such understanding is fundamental for the design and application of effective interventions targeting fall prevention.

Methods

We systematically searched the Web of Science, MEDLINE, Embase and Science Direct databases as well as the reference lists of the eligible articles. A study was included if it addressed an investigation of the locomotor adaptability in response to repeated mechanical movement perturbations of healthy older adults (≥60 years). The weighted average effect size (WAES) of the general adaptability (adaptive motor responses to repeated perturbations) as well as predictive (after-effects) and reactive adaptation (feedback responses to a recurring unexpected perturbation) was calculated and tested for an overall effect. A subgroup analysis was performed regarding the factor age group [i.e., young (≤35 years) vs. older adults]. Furthermore, the methodological study quality was assessed.

Results

The review process yielded 18 studies [1009 participants, 613 older adults (70 ± 4 years)], which used various kinds of locomotor tasks and perturbations. The WAES for the general locomotor adaptability was 1.21 [95 % confidence interval (CI) 0.68–1.74, n = 11] for the older and 1.39 (95 % CI 0.90–1.89, n = 10) for the young adults with a significant (p < 0.05) overall effect for both age groups and no significant subgroup differences. Similar results were found for the predictive (older: WAES 1.10, 95 % CI 0.37–1.83, n = 8; young: WAES 1.54, 95 % CI 0.11–2.97, n = 7) and reactive (older: WAES 1.09, 95 % CI 0.22–1.96, n = 5; young: WAES 1.35, 95 % CI 0.60–2.09, n = 5) adaptation featuring significant (p < 0.05) overall effects without subgroup differences. The average score of the methodological quality was 67 ± 8 %.

Conclusions

The present meta-analysis provides elaborate statistical evidence that locomotor adaptability in general and predictive and reactive adaptation in particular remain highly effective in the elderly, showing only minor, not statistically significant age-related deficits. Consequently, interventions which use adaptation and learning paradigms including the application of the mechanisms responsible for an effective predictive and reactive dynamic stability control may progressively improve older adults’ recovery performance and, thus, reduce their risk of falling.

Electronic supplementary material

The online version of this article (doi:10.1007/s40279-015-0413-9) contains supplementary material, which is available to authorized users.

Chronic Eccentric Exercise and the Older Adult

Eccentric exercise has gained increasing attention as a suitable and promising intervention to delay or mitigate the known physical and physiological declines associated with aging. Determining the relative efficacy of eccentric exercise when compared with the more conventionally prescribed traditional resistance exercise will support evidence-based prescribing for the aging population. Thus, original research studies incorporating chronic eccentric exercise interventions in the older adult population were included in this review. The effects of a range of eccentric exercise modalities on muscular strength, functional capacity, body composition, muscle architecture, markers of muscle damage, the immune system, cardiovascular system, endocrine system, and rating of perceived exertion were all reviewed as outcomes of particular interest in the older adult. Muscular strength was found to increase most consistently compared with results from traditional resistance exercise. Functional capacity and body composition showed significant improvements with eccentric endurance protocols, especially in older, frail or sedentary cohorts. Muscle damage was avoided with the gradual progression of novel eccentric exercise, while muscle damage from intense acute bouts was significantly attenuated with repeated sessions. Eccentric exercise causes little cardiovascular stress; thus, it may not generate the overload required to elicit cardiovascular adaptations. An anabolic state may be achievable following eccentric exercise, while improvements to insulin sensitivity have not been found. Finally, rating of perceived exertion during eccentric exercise was often significantly lower than during traditional resistance exercise. Overall, evidence supports the prescription of eccentric exercise for the majority of outcomes of interest in the diverse cohorts of the older adult population.

Age-related maintenance of eccentric strength: a study of temperature dependence

With adult aging, eccentric strength is maintained better than isometric strength leading to a higher ratio of eccentric/isometric force production (ECC/ISO) in older than younger adults. The purpose was to investigate the ECC/ISO during electrical activation of the adductor pollicis during lengthening (20-320° s(-1)) contractions in 24 young (n = 12, ∼24 years) and old (n = 12, ∼72 years) males across muscle temperatures (cold ∼19 °C; normal ∼30 °C; warm ∼35 °C). For isometric force, the old were 20-30 % weaker in the normal and cold conditions (P < 0.05) with no difference for the warm condition compared to young (P > 0.05). Half-relaxation time (HRT) did not differ across age for the normal and warm temperatures (P > 0.05), but it slowed significantly for old in the cold condition compared with young (∼15 %; P < 0.05), as well, there was a 20 and 40 % increase in muscle stiffness for the young and old, respectively. ECC/ISO was 50-60 % greater for the cold condition than the normal and warm conditions. There was no age difference in ECC/ISO across ages for the normal and warm conditions (P > 0.05), but for the cold, the old exhibited a 20-35 % higher ECC/ISO than did the young for velocities above 60° s(-1) (P < 0.05). A contributing factor to the elevated ECC/ISO is an increased proportion of weakly compared to strongly bound crossbridges. These findings highlight the relationship (r = 0.70) between intrinsic muscle contractile speed (HRT) and eccentric strength in old age.

Effects of age and muscle action type on acute strength and power recovery following fatigue of the leg flexors

Short-term strength and power recovery patterns following fatigue have received little research attention, particularly as they pertain to age-specific responses, and the leg flexors (i.e., hamstrings) muscle group. Thus, research is warranted addressing these issues because both age-related alterations in the neuromuscular system and mode of muscle action (e.g., eccentric, concentric, isometric) may differentially influence recovery responses from fatigue. The aim of this study was to investigate the strength and power recovery responses for eccentric, concentric, and isometric muscle actions of the leg flexors in young and older men following an isometric, intermittent fatigue-inducing protocol. Nineteen young (age = 25 ± 3 years) and nineteen older (71 ± 4) men performed maximal voluntary contractions (MVCs) for eccentric, concentric, and isometric muscle actions followed by a fatigue protocol of intermittent (0.6 duty cycle) isometric contractions of the leg flexors at 60% of isometric MVC. MVCs of each muscle action were performed at 0, 7, 15, and 30 min following fatigue. Peak torque (PT) and mean power values were calculated from the MVCs and the eccentric/concentric ratio (ECR) was derived. For PT and mean power, young men showed incomplete recovery at all time phases, whereas the older men had recovered by 7 min. Eccentric and isometric muscle actions showed incomplete recovery at all time phases, but concentric recovered by 7 min, independent of age. The ECR was depressed for up to 30 min following fatigue. More rapid and pronounced recovery in older men and concentric contractions may be related to physiological differences specific to aging and muscle action motor unit patterns. Individuals and clinicians may use these time course responses as a guide for recovery following activity-induced fatigue.

17β-Estradiol and testosterone in sarcopenia: Role of satellite cells

The loss of muscle mass and strength with aging, referred to as sarcopenia, is a prevalent condition among the elderly. Although the molecular mechanisms underlying sarcopenia are unclear, evidence suggests that an age-related acceleration of myocyte loss via apoptosis might be responsible for muscle perfomance decline. Interestingly, sarcopenia has been associated to a deficit of sex hormones which decrease upon aging. The skeletal muscle ability to repair and regenerate itself would not be possible without satellite cells, a subpopulation of cells that remain quiescent throughout life. They are activated in response to stress, enabling them to guide skeletal muscle regeneration. Thus, these cells could be a key factor to overcome sarcopenia. Of importance, satellite cells are 17β-estradiol (E2) and testosterone (T) targets. In this review, we summarize potential mechanisms through which these hormones regulate satellite cells activation during skeletal muscle regeneration in the elderly. The advance in its understanding will help to the development of potential therapeutic agents to alleviate and treat sarcopenia and other related myophaties.