Changes in muscle force–length properties affect the early rise of force in vivo

Changes in contractile rate of force development (RFD), measured within a short time interval from contraction initiation, were measured after a period of strength training that led to increases in muscle fascicle length but no measurable change in neuromuscular activity. The relationship between training‐induced shifts in the moment–angle relation and changes in RFD measured to 30 ms (i.e., early) and 200 ms (i.e., late) from the onset of isometric knee extension force were examined; shifts in the moment–angle relation were used as an overall measure of changes in quadriceps muscle fascicle length. A significant proportion of the variance in RFD measured only in the initial contraction phase (0–30 ms) could be explained by shifts in the moment–angle relation (r = ?0.66–0.71; R² = 0.44–0.50). Training‐induced increases in muscle fascicle length may lead to a reduced or complete lack of adaptive gains in contractile RFD, especially in the early contraction phase. Muscle Nerve 39: 512–520, 2009     

Load‐controlled moderate and high‐intensity resistance training programs provoke similar strength gains in young women

Introduction: While current exercise guidelines recommend progressive, high‐intensity resistance training (RT) to promote muscle hypertrophy and strength gains, controversy exists regarding the efficacy of lighter‐load RT. We compared 2 work‐matched RT interventions that differed in training intensity. Methods: Fifteen women underwent 10 weeks of unilateral knee extensor RT. One leg was trained at increasing intensity (intensity leg, InL, 50–80% 1‐repetition maximum [1‐RM]), and training progression in the contralateral leg (volume leg, VoL, 50% 1‐RM) was based on increasing training volumes. Quadriceps muscle size (ultrasound, dual energy X‐ray absorptiometry) and strength (isokinetic dynamometry) were assessed on 4 occasions. Results: Both training programs induced significant, yet comparable increases in muscle size (InL: +4.6–12%, VoL: +3.1–11%) and strength (InL: +10–16%, VoL: +10–14%). Conclusions: Training at lower than commonly suggested intensities may be an equally effective alternative form of RT. Factors other than training intensity, such as the total mechanical work during training, may strongly affect the training response. Muscle Nerve 51 : 92–101, 2015     

Resistance training and aerobic training improve muscle strength and aerobic capacity in chronic inflammatory demyelinating polyneuropathy

Introduction: We investigated the effects of aerobic and resistance exercise in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). Methods: Eighteen CIDP patients treated with subcutaneous immunoglobulin performed 12 weeks of aerobic exercise and 12 weeks of resistance exercise after a run‐in period of 12 weeks without exercise. Three times weekly the participants performed aerobic exercise on an ergometer bike or resistance exercise with unilateral training of knee and elbow flexion/extension. Primary outcomes were maximal oxygen consumption velocity (VO₂‐max) and maximal combined isokinetic muscle strength (cIKS) of knee and elbow flexion/extension. Results: VO₂‐max and muscle strength were unchanged during run‐in (?4.9% ± 10.3%, P = 0.80 and ?3.7% ± 10.1%, P = 0.17, respectively). Aerobic exercise increased VO₂‐max by 11.0% ± 14.7% (P = 0.02). Resistance exercise resulted in an increase of 13.8% ± 16.0% (P = 0.0004) in cIKS. Discussion: Aerobic exercise training and resistance exercise training improve fitness and strength in CIDP patients. Muscle Nerve 57 : 70–76, 2018     

Effect of contraction mode of slow-speed resistance training on the maximum rate of force development in the human quadriceps

This study examined the effects of slow-speed resistance training involving concentric (CON, n = 10) versus eccentric (ECC, n = 11) single-joint muscle contractions on contractile rate of force development (RFD) and neuromuscular activity (EMG), and its maintenance through detraining. Isokinetic knee extension training was performed 3 x week(-1) for 10 weeks. Maximal isometric strength (+11.2%) and RFD (measured from 0-30/50/100/200 ms, respectively; +10.5%-20.5%) increased after 10 weeks (P < 0.01-0.05); however, there was no effect of training mode. Peak EMG amplitude and rate of EMG rise were not significantly altered with training or detraining. Subjects with below-median normalized RFD (RFD/MVC) at 0 weeks significantly increased RFD after 5- and 10-weeks training, which was associated with increased neuromuscular activity. Subjects who maintained their higher RFD after detraining also exhibited higher activity at detraining. Thus, only subjects with a lesser ability to rapidly attain their maximum force before training improved RFD with slow-speed resistance exercise.     

Diurnal and day‐to‐day variation of isometric muscle strength in myasthenia gravis

Introduction: In patients with myasthenia gravis (MG), muscle strength is expected to decrease gradually during the day due to physical activities. Methods: Isometric muscle strength at the shoulder, knee, and ankle was determined in 10 MG patients (MGFA class II–IV) who were receiving usual medical treatment and in 10 control subjects. To determine diurnal and day‐to‐day variation, muscle strength was measured 4 times during day 1 and once at day 2. Results: Knee extension strength decreased during the day in both patients and controls. Neither diurnal nor day‐to‐day variation of muscle strength was higher in patients compared with controls. Conclusions: Patients with mild to moderate MG did not have increased variation of isometric muscle strength during the day or from day‐to‐day compared with controls. This suggests that isometric muscle performance can be determined with high reproducibility in similar groups of MG patients without regard to time of day. Muscle Nerve 53 : 67–72, 2016     

Relative differences in strength and power from slow to fast isokinetic velocities may reflect dynapenia

Introduction: We compared absolute and normalized values for peak torque (PT), mean power (MP), rate of velocity development, and electromyography (EMG) amplitude during maximal isometric and concentric isokinetic leg extension muscle actions, as well as the %decrease in PT and %increase in MP from 1.05 to 3.14 rad·s^?1 in younger versus older men. Methods: Measurements were performed twice for reliability. Isokinetic measurements were normalized to the isometric muscle actions. Results: Absolute isometric PT, isokinetic PT and MP, and EMG amplitudes at 1.05 and 3.14 rad·s^?1 were greater in the younger men, although normalizing to isometric PT eliminated the age differences. The older men exhibited greater %decrease in PT (37.2% vs. 31.3%) and lower %increase in MP (87.6% vs. 126.4%) regardless of normalization. Conclusions: Normalization eliminated absolute differences in isokinetic strength and power, but the relative differences from slow to fast velocities may reflect dynapenia characterized by age‐related decreases in fast‐twitch fiber function. Muscle Nerve 52 : 120–130, 2015     

Effects of unilateral electromyostimulation superimposed on voluntary training on strength and cross‐sectional area

In this study we investigate the effects of unilateral voluntary contraction (VC) and electromyostimulation superimposed on VC (EV) training on maximal voluntary (MVC) force and cross‐sectional area (CSA), as assessed by magnetic resonance imaging of knee extensors. Thirty young men were randomly assigned to either a control group (CG), VC group (VG), or EV group (EVG). The VG and EVG trained the right leg isometrically three sessions per week for 6 weeks. After training, MVC increased in the right leg in the VG and in both legs in the EVG, and EVG was significantly different from CG (all P < 0.01). Increased CSA was found only in the right leg in the VG and EVG (P < 0.01), and correlated with improvements of MVC (r = 0.49, P = 0.01). It appeared that the EV training was equally effective as VC at increasing MVC and CSA, while having a greater cross‐education effect. Increased strength without muscle hypertrophy in the unexercised leg of the EVG indicated that neural adaptation was responsible for the cross‐education effect. Muscle Nerve 40: 430–437, 2009     

Low‐volume resistance exercise attenuates the decline in strength and muscle mass associated with immobilization

We determined the effectiveness of low‐volume resistance exercise (EX) for the attenuation of loss of muscle mass and strength during leg immobilization. Men (N = 5) and women (N = 12, age 24 ± 5 years, body mass index 25.4 ± 3.6 kg/m²) were divided into two groups: exercise (EX; n = 12) and control (CON; n = 5). Subjects wore a knee brace on one leg that prevented weight bearing for 14 days. Resistance exercise (EX; 80% of maximal) was performed by the immobilized limb every other day. Immobilization induced a significant reduction (P < 0.05) in muscle fiber and thigh cross‐sectional area (CSA), isometric knee extensor, and plantarflexor strength in the CON (P < 0.01) but not in the EX group. There were significant losses in triceps surae CSA in the CON and EX groups (P < 0.05), but the losses were greater in CON subjects (P < 0.01). A minimal volume (140 contractions in 14 days) of resistive exercise is an effective countermeasure against immobilization‐induced atrophy of the quadriceps femoris but is only partially effective for the triceps surae. Muscle Nerve, 2010     

Effectiveness of functional progressive resistance exercise strength training on muscle strength and mobility in children with cerebral palsy: a randomized controlled trial

Aim To evaluate the effectiveness of functional progressive resistance exercise (PRE) strength training on muscle strength and mobility in children with cerebral palsy (CP). Method Fifty‐one children with spastic uni‐ and bilateral CP; (29 males, 22 females; mean age 10y 5mo, SD 1y 10mo, range 6y 0mo–13y 10mo; Gross Motor Function Classification System levels I–III) were randomized to the intervention group (n=26) or the control group (n=25, receiving usual care). The intervention group trained for 12 weeks, three times a week, on a five‐exercise circuit, which included a leg‐press and functional exercises. The training load progressively increased based on the child’s maximum level of strength, determined by the eight‐repetition maximum. Muscle strength (measured with hand‐held dynamometry and a six‐repetition maximum leg‐press test), mobility (measured with the Gross Motor Function Measure, two functional tests, and a mobility questionnaire), and spasticity (measured by the appearance of a catch) were evaluated before, during, directly after, and 6 weeks after the end of training by two blinded research assistants. Results Directly after training, there was a statistically significant effect (p<0.05) on muscle strength (knee extensors +12% [0.56N/kg; 95% confidence interval {CI} 0.13–0.99]; hip abductors +11% [0.27N/kg; 95% CI 0.00–0.54]; total +8% [1.30N/kg; 95% CI 0.56–2.54]; six‐repetition maximum +14% [14%; 95% CI 1.99–26.35]), but not on mobility or spasticity. A detraining effect was seen after 6 weeks. Interpretation Twelve weeks of functional PRE strength training increases muscle strength up to 14%. This strength gain did not lead to improved mobility.     

Feasibility and reliability of measuring strength, sprint power, and aerobic capacity in athletes and non-athletes with cerebral palsy

Aim The aim of this study was to analyse the feasibility and reliability of the tests used to determine muscle strength, sprint power, and aerobic capacity in athletes and non‐athletes with cerebral palsy (CP). Methods Twenty individuals with spastic CP (four females, 16 males; age range 18–49y; Gross Motor Function Classification System level I, n=15; II, n=5; unilateral CP, n=10; bilateral CP, n=10; athletes, n=12; non‐athletes, n=8) participated in the study. Isometric and isokinetic knee flexor and extensor strength, sprint power, and aerobic capacity were determined, using, respectively an isokinetic dynamometer, a Wingate cycling test, and a graded maximal bicycle exercise test, on three occasions. Intraclass correlation coefficients (ICC), standard error of measurements, and smallest detectable differences (SDD) were calculated. Results The feasibility of the isometric strength test, Wingate test, and graded exercise test was good; the isokinetic strength test was difficult to perform for five participants. The strength parameters showed moderate to good ICCs (isometric, 0.74–0.94; isokinetic, 0.88–0.93) but high SDDs (isometric, 25–45%; isokinetic, 30–45%). Sprint power (ICC 0.98; SDD 24%) and aerobic capacity (ICC 0.98–0.99; SDD 16–21%) showed good ICCs and moderate SDDs. Interpretation All tests, except for the isokinetic strength test, seemed to be feasible for almost all participants. All tests are suitable for evaluating changes in a group; however, only large improvements (16–45%) can be detected when monitoring individual changes.     

Training at non‐damaging intensities facilitates recovery from muscle atrophy

Introduction: Resistance training promotes recovery from muscle atrophy, but optimum training programs have not been established. We aimed to determine the optimum training intensity for muscle atrophy. Methods: Mice recovering from atrophied muscles after 2 weeks of tail suspension underwent repeated isometric training with varying joint torques 50 times per day. Results: Muscle recovery assessed by maximal isometric contraction and myofiber cross‐sectional areas (CSAs) were facilitated at 40% and 60% maximum contraction strength (MC), but at not at 10% and 90% MC. At 60% and 90% MC, damaged and contained smaller diameter fibers were observed. Activation of myogenic satellite cells and a marked increase in myonuclei were observed at 40%, 60%, and 90% MC. Conclusions: The increases in myofiber CSAs were likely caused by increased myonuclei formed through fusion of resistance‐induced myofibers with myogenic satellite cells. These data indicate that resistance training without muscle damage facilitates efficient recovery from atrophy. Muscle Nerve 55 : 243–253, 2017     

Axonal excitability during ischemia in MELAS

Introduction: We investigated muscle activation strategy and performance of knee extensor and flexor muscles in children and adults with generalized joint hypermobility (GJH) and compared them with controls. Methods: Muscle activation, torque steadiness, electromechanical delay, and muscle strength were evaluated in 39 children and 36 adults during isometric knee extension and flexion. Subjects performed isometric maximum contractions, submaximal contractions at 25% maximum voluntary contraction (MVC), and explosive contractions. Results: Agonist activation was reduced, and coactivation ratio was greater in GJH during knee flexion compared with controls. Torque steadiness was impaired in adults with GJH during knee flexion. No effect of GJH was found on muscle strength or electromechanical delay. Correlation analysis revealed an association between GJH severity and function in adults. Conclusions: The results indicate that muscle activation strategy and quality of force control were significantly affected in adults with GJH during knee flexion, whereas only muscle activation strategy was affected in children with GJH. Muscle Nerve 48:762–769, 2013     

Endurance neuromuscular electrical stimulation training improves skeletal muscle oxidative capacity in individuals with motor‐complete spinal cord injury

Introduction: Spinal cord injury (SCI) results in skeletal muscle atrophy, increases in intramuscular fat, and reductions in skeletal muscle oxidative capacity. Endurance training elicited with neuromuscular electrical stimulation (NMES) may reverse these changes and lead to improvement in muscle metabolic health. Methods: Fourteen participants with complete SCI performed 16 weeks of home‐based endurance NMES training of knee extensor muscles. Skeletal muscle oxidative capacity, muscle composition, and blood metabolic and lipid profiles were assessed pre‐ and post‐training. Results: There was an increase in number of contractions performed throughout the duration of training. The average improvement in skeletal muscle oxidative capacity was 119%, ranging from –14% to 387% (P = 0.019). There were no changes in muscle composition or blood metabolic and lipid profiles. Conclusion: Endurance training improved skeletal muscle oxidative capacity, but endurance NMES of knee extensor muscles did not change blood metabolic and lipid profiles. Muscle Nerve 55: 669–675, 2017     

Knee extensor fatigue resistance of young and older men and women performing sustained and brief intermittent isometric contractions

Introduction: Susceptibility to muscle fatigue during aging could depend on muscle activation patterns. Methods: Young (mean age, 22 years) and older (mean age 70 years) men and women completed two fatigue tests of knee extensor muscles using voluntary and electrically stimulated contractions. Results: Older subjects displayed a shift to the left of the torque‐frequency relationship and held a sustained voluntary isometric contraction at 50% maximal strength for significantly longer than young (P < 0.001). Young and old showed similar fatigue during electrically induced, intermittent isometric contractions (1‐s on, 1‐s off for 2 min), but women fatigued less than men (P = 0.001). Stronger muscles fatigued more quickly, and slower contractile properties were associated with longer sustained contractions. Conclusions: The slowing and weakness of older muscle was associated with superior fatigue resistance during sustained isometric contractions. Young and old showed similar fatigue following a series of brief, intermittent contractions, but women fatigued less than men. Muscle Nerve 50 : 393–400, 2014     

Muscle architecture and strength: Adaptations to short‐term resistance training in older adults

Introduction: Muscle morphology and architecture changes in response to 6 weeks of progressive resistance training were examined in healthy older adults. Methods: In this randomized, controlled design, muscle strength, quality, and architecture were evaluated with knee extension, DEXA, and ultrasound, respectively, in 25 older adults. Results: Resistance training resulted in significant increases in strength and muscle quality of 32% and 31%, respectively. Cross‐sectional area of the vastus lateralis increased by 7.4% (p ≤ 0.05). Physiological cross‐sectional area (PCSA) of the thigh, a composite measure of muscle architecture, was related significantly to strength (r = 0.57; p ≤ 0.01) and demonstrated a significant interaction after training (p ≤ 0.05). Change in PCSA of the vastus lateralis was associated with change in strength independent of any other measure. Conclusions: Six weeks of resistance training was effective at increasing strength, muscle quality, and muscle morphology in older adult men and women. Muscle Nerve 49:584–592, 2014     

Variability and distribution of muscle strength and its determinants in humans

Introduction: Inter‐individual variability in measurements of muscle strength and its determinants was identified to: (1) produce a normative data set describing the normal range and (2) determine whether some measurements are more informative than others when evaluating inter‐individual differences. Methods: Functional and morphological characteristics of the vastus lateralis were measured in 73 healthy, untrained adult men. Results: Inter‐individual variability (coefficient of variation) was greater for isometric maximal voluntary contraction (MVC) torque (18.9%) compared with fascicle force (14.6%; P = 0.025) and physiological cross‐sectional area (PCSA; 17.2%) compared with anatomical cross‐sectional area (ACSA, 13.0%; P < 0.0005). The relationship between ACSA and isometric MVC torque (r² = 0.56) was weaker than that between PCSA and fascicle force (r² = 0.68). Conclusions: These results provide a normative data set on inter‐individual variability in a variety of muscle strength‐related measurements and illustrate the benefit of using more stringent measures of muscle properties. Muscle Nerve 49 : 879–886, 2014     

Effects of whole body vibration training on people with chronic stroke: a systematic review and meta-analysis

Abstract

Background:

The effects of whole body vibration (WBV) on chronic stroke (CS) patients have been investigated by some previous studies. However, controversy still exists.

Objective:

The objective of this meta-analysis was to review existing studies that assess the effects of WBV training on CS patients.

Methods:

We searched Medline, Web of Science, EMBASE, and the Cochrane Library for papers published between January 2000 and January 2014.The meta-analyses were performed using Review Manage Version 5.2.Weighted mean difference (WMD) or standard mean difference (SMD) and its 95% confidence intervals (CI) were used as summary statistics. Funnel plot was used to assess the publication bias.

Results:

Seven studies with 298 CS patients (159 patients underwent WBV training in experimental group and 139 patients underwent nothing or the same exercise without vibration or with a “placebo” vibrating platform in control group) were included. No significant difference was found in muscle strength (isometric knee extension strength: SMD?=???0.15, 95% CI, ??0.43 to 0.13, P?=?0.30; isometric knee flexion strength: WMD?=???0.05, 95% CI, ??0.13 to 0.03, P?=?0.22), balance (berg balance scale, WMD?=???0.23, 95% CI, ??1.54 to 1.09; P?=?0.74) and gait performance (6-min walk test, WMD?=???50.40, 95% CI, ??118.14 to 17.34; P?=?0.14) between groups. No indication of publication bias was found in the funnel plot.

Conclusions:

WBV training had no beneficial effects in muscle strength, balance and gait performance of CS patients.     

Cross‐education after high‐frequency versus low‐frequency volume‐matched handgrip training

Introduction: Cross‐education training programs cause interlimb asymmetry of strength and hypertrophy. We examined the cross‐education effects from a high‐frequency (HF) versus a low‐frequency (LF) volume‐matched handgrip training program on interlimb asymmetry. Methods: Right‐handed participants completed either HF (n = 10; 2 × 6 repetitions 10 times per week) or LF (n = 9; 5 × 8 repetitions 3 times per week) training. Testing occurred twice before and once after 4 weeks of right‐handed isometric handgrip training totaling 120 weekly repetitions. Measures were maximal isometric handgrip and wrist flexion torque, muscle thickness, and muscle activation (electromyography; EMG). Results: Grip strength was greater in both limbs posttraining, pooled across groups (P < 0.001). Trained limb muscle thickness increased in both groups (P < 0.05; untrained, P = 0.897). EMG and wrist flexion torque did not change (all P > 0.103). Discussion: Both LF and HF induced cross‐education of grip strength to the untrained limb, but HF did not reduce asymmetry. These findings have implications for injury rehabilitation. Muscle Nerve 56 : 689–695, 2017     

Stroke‐related effects on maximal dynamic hip flexor fatigability and functional implications

Introduction: Stroke‐related changes in maximal dynamic hip flexor muscle fatigability may be more relevant functionally than isometric hip flexor fatigability. Methods: Ten chronic stroke survivors performed 5 sets of 30 hip flexion maximal dynamic voluntary contractions (MDVC). A maximal isometric voluntary contraction (MIVC) was performed before and after completion of the dynamic contractions. Both the paretic and nonparetic legs were tested. Results: Reduction in hip flexion MDVC torque in the paretic leg (44.7%) was larger than the nonparetic leg (31.7%). The paretic leg had a larger reduction in rectus femoris EMG (28.9%) between the first and last set of MDVCs than the nonparetic leg (7.4%). Reduction in paretic leg MDVC torque was correlated with self‐selected walking speed (r² = 0.43), while reduction in MIVC torque was not (r² = 0.11). Conclusions: Reductions in maximal dynamic torque of paretic hip flexors may be a better predictor of walking function than reductions in maximal isometric contractions. Muscle Nerve 51 : 446–448, 2015     

Knee extensor strength exhibits potential to predict function in sporadic inclusion-body myositis

Introduction: In this study we address the challenging issue of potential use of muscle strength to predict function in clinical trials. This has immediate relevance to translational studies that attempt to improve quadriceps strength in sporadic inclusion‐body myositis (sIBM). Methods: Maximum voluntary isometric contraction testing as a measure of muscle strength and a battery of functional outcomes were tested in 85 ambulatory subjects with sIBM. Results: Marked quadriceps weakness was noted in all patients. Strength was correlated with distance walked at 2 and 6 minutes. Additional correlations were found with time to get up from a chair, climb stairs, and step up on curbs. Conclusions: Quadriceps (knee extensor) strength correlated with performance in this large cohort of sIBM subjects, which demonstrated its potential to predict function in this disease. These data provide initial support for use of muscle strength as a surrogate for function, although validation in a clinical trial is required. Muscle Nerve, 2012