Neural Adaptations to Resistive Exercise

Effects of training on the estimation of muscular moment in submaximal exercise

The purpose of this study was to observe the effects of a submaximal isometric training program on estimation capacity at 25, 50, and 75% of maximal contraction in isometric action and at two angular velocities. The second purpose was to study the variability of isometric action. To achieve these purposes, participants carried out an isokinetic extension movement of the dominant lower limb during six test sessions and nine training sessions. Following the training program, estimation capacity in the different actions did not improve. However an improvement in performance was observed with a reduction in the variability of submaximal isometric actions. The proprioceptors activated in isometric action seemed to adapt to the training program itself which would promote better adaptation by a greater solicitation of internal feedback.

Effect of head and neck position on outcome of quantitative neuromuscular diagnostic techniques in Warmblood riding horses directly following moderate exercise

REASONS FOR PERFORMING STUDY

There has been growing interest in training techniques with respect to the head and neck position (HNP) of the equine athlete. Little is known about the influence of HNP on neuromuscular transmission in neck muscles.

OBJECTIVE

To test the hypothesis that different HNPs have effect on single fibre (SF), quantitative electromyographic (QEMG) examination and muscle enzyme activity directly after moderate exercise.

METHODS

Seven Warmblood horses were studied using a standard exercise protocol in 5 HNPs: HNP1: unrestrained; HNP2: neck raised; bridge of nose around the vertical; HNP4: neck lowered and considerably flexed, bridge of nose pointing towards the chest; HNP5: neck raised and considerably extended; bridge of nose in front of the vertical; HNP7: neck lowered and flexed; bridge of nose pointing towards the carpus. Mean consecutive difference (MCD) of single muscle fibre potentials and motor unit action potential (MUP) variables (amplitude, duration, area, turns and phases) were recorded in each fixed position directly after exercise at rest using commercial EMG equipment. Muscle enzyme activity was measured before and 4, 6 and 24 h after exercise.

RESULTS

Mean consecutive difference in all HNPs was higher than in HNP1 (22 µs, P < 0.001) of which HNP4 was highest with 39 µs compared to 30 µs in HNP2 (P = 0.04); MCD in HNP 5,7 was with 25 µs lower than in HNP 2 and 4 (P < 0.001). Odds ratio for MCD suggestive for conduction delay or block was 13.6 in HNP4 compared to HNP1 (P < 0.001). Motion unit action potential variables followed the same pattern as MCD. Lactate dehydrogenase (LDH) activity increased in HNP4 at 4 h (P = 0.014), 6 h (P = 0.017) and 24 h (P = 0.038) post exercise and in HNP5 and HNP7 at 4 h (P = 0.037; 0.029).

CONCLUSIONS AND CLINICAL RELEVANCE

HNP4 in particular leads to a higher rise in LDH activity, MCD and MUP variables, indicating that HNPs have effect on variables characterising neuromuscular functionality.

Effects of high-intensity exercise and protein supplement on muscle mass in ADL dependent older people with and without malnutrition: a randomized controlled trial

BACKGROUND

Loss of muscle mass is common among old people living in institutions but trials that evaluate interventions aimed at increasing the muscle mass are lacking. Objective, participants and intervention: This randomized controlled trial was performed to evaluate the effect of a high-intensity functional exercise program and a timed protein-enriched drink on muscle mass in 177 people aged 65 to 99 with severe physical or cognitive impairments, and living in residential care facilities.

DESIGN

Three-month high-intensity exercise was compared with a control activity and a protein-enriched drink was compared with a placebo drink. A bioelectrical impedance spectrometer (BIS) was used in the evaluation. The amount of muscle mass and body weight (BW) were followed-up at three and six months and analyzed in a 2 x 2 factorial ANCOVA, using the intention to treat principle, and controlling for baseline values.

RESULTS

At 3-month follow-up there were no differences in muscle mass and BW between the exercise and the control group or between the protein and the placebo group. No interaction effects were seen between the exercise and nutritional intervention. Long-term negative effects on muscle mass and BW was seen in the exercise group at the 6-month follow-up.

CONCLUSION

A three month high-intensity functional exercise program did not increase the amount of muscle mass and an intake of a protein-enriched drink immediately after the exercise did not induce any additional effect on muscle mass. There were negative long-term effects on muscle mass and BW, indicating that it is probably necessary to compensate for an increased energy demand when offering a high-intensity exercise program.

Early neural responses to strength training

The neural adaptations that accompany strength training have yet to be fully determined. Here we sought to address this topic by testing the idea that strength training might share similar mechanisms with some forms of motor learning. Since ballistic motor learning is accompanied by a shift in muscle twitches induced by transcranial magnetic stimulation (TMS) toward the training direction, we sought to investigate if these changes also occur after single isometric strength training sessions with various contraction duration and rate of force development characteristics (i.e., brief or sustained ballistic contractions or slow, sustained contractions). Twitch force resultant vectors and motor-evoked potentials (MEPs) induced by TMS were measured before and after single sessions of strength training involving the forearm muscles. Participants ( n = 12) each performed three training protocols (each consisting of 4 sets of 10 repetitions) and served as their own control in a counterbalanced order. All three training protocols caused a significant ( P < 0.05) shift in TMS-induced twitch force resultant vectors toward the training direction, followed by a gradual shift back toward the pretraining direction. The strongest effect was found when training involved both ballistic and sustained force components. There were no large or consistent changes in the direction of twitches evoked by motor nerve stimulation for any of the three training protocols. We suggest that these early neural responses to strength training, which share similar corticospinal changes to motor learning, might reflect an important process that precedes more long-term neural adaptation that ultimately enhance strength.

Activation of selected shoulder muscles during unilateral wall and bench press tasks under submaximal isometric effort

STUDY DESIGN

Controlled laboratory study.

OBJECTIVE

To assess the activation of 7 shoulder muscles under 2 closed kinetic chain (CKC) tasks for the upper extremity using submaximal isometric effort, thus providing relative quantification of muscular isometric effort for these muscles across the CKC exercises, which may be applied to rehabilitation protocols for individuals with shoulder weakness.

BACKGROUND

CKC exercises favor joint congruence, reduce shear load, and promote joint dynamic stability. Additionally, knowledge about glenohumeral and periscapular muscle activity elicited during CKC exercises may help clinicians to design protocols for shoulder rehabilitation.

METHODS

Using surface electromyography, activation level was measured across 7 shoulder muscles in 20 healthy males, during the performance of a submaximal isometric wall press and bench press. Signals were normalized to the maximal voluntary isometric contraction, and, using paired t tests, data were analyzed between the exercises for each muscle.

RESULTS

Compared to the wall press, the bench press elicited higher activity for most muscles, except for the upper trapezius. Levels of activity were usually low but were above 20% maximal voluntary isometric contraction for the serratus anterior on both tasks, and for the long head triceps brachii on the bench press.

CONCLUSIONS

Both the bench press and wall press, as performed in this study, led to relatively low EMG activation levels for the muscles measured and may be considered for use in the early phases of rehabilitation.

Neural adaptations to electrical stimulation strength training

This review provides evidence for the hypothesis that electrostimulation strength training (EST) increases the force of a maximal voluntary contraction (MVC) through neural adaptations in healthy skeletal muscle. Although electrical stimulation and voluntary effort activate muscle differently, there is substantial evidence to suggest that EST modifies the excitability of specific neural paths and such adaptations contribute to the increases in MVC force. Similar to strength training with voluntary contractions, EST increases MVC force after only a few sessions with some changes in muscle biochemistry but without overt muscle hypertrophy. There is some mixed evidence for spinal neural adaptations in the form of an increase in the amplitude of the interpolated twitch and in the amplitude of the volitional wave, with less evidence for changes in spinal excitability. Cross-sectional and exercise studies also suggest that the barrage of sensory and nociceptive inputs acts at the cortical level and can modify the motor cortical output and interhemispheric paths. The data suggest that neural adaptations mediate initial increases in MVC force after short-term EST.

Non-invasive physiological monitoring of exercise and fitness

OBJECTIVE

To review the current research of new emerging diagnostic technology for non-invasive physiological monitoring of exercise and fitness. As a personal trainer, I believe that exercise can improve the conditions of several diseases and/or events such as stroke, post-traumatic head injury, spinal cord injury, and a multitude of other diseases. This compilation of information will allow health care providers tools of a non-invasive manner to promote healing and health that go beyond the initial event. Allowing patients continued managed care beyond what is believed to be their plateau.

MATERIAL AND METHOD

Review science-based research involving non-invasive technology, including cardiovascular evaluations: heart rate monitors, near-infrared spectroscopy, blood pressure, and electrocardiography; motor capabilities: surface electromyography and manual testers, i.e. dynamometer, and digital and video photography; radiological monitoring: magnetic resonance imaging, three-dimensional computer tomography, and laser Doppler.

RESULTS

This investigation has found that a new approach should be implemented for non-invasive physiological monitoring of exercise and fitness through development and utilization across a wide variety of equipment, and monitoring technology. This non-invasive methodology will not only motivate but encourage individuals to begin and remain compliant with an exercise program allowing a variety of health care providers to assist in patient care.

DISCUSSION

We need to shift the paradigm from taking care of the sick to maintaining the health of our patients. This can be accomplished with non-invasive evaluation, tracking, and monitoring tools. Many of the suggestions for monitoring are used in a clinical setting rather than a general fitness environment. These monitoring tests need to be economical as well as available for continual re-evaluation.

The effects of exercise for the prevention of overuse anterior knee pain: a randomized controlled trial

BACKGROUND

Anterior knee pain (AKP) is the most common activity-related injury of the knee. The authors investigated the effect of an exercise intervention on the incidence of AKP in UK army recruits undergoing a 14-week physically arduous training program.

HYPOTHESIS

Modifying military training to include targeted preventative exercises may reduce the incidence of AKP in a young recruit population.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A single-blind cluster randomized controlled trial was performed in 39 male and 11 female training groups (median age: 19.7 years; interquartile range, 17-25) undergoing phase 1 of army recruit training. Each group was randomly assigned to either an intervention (n = 759) or control (n = 743) protocol. The intervention consisted of 4 strengthening and 4 stretching exercises completed during supervised physical training lessons (7 per week). The control group followed the existing training syllabus warm-up exercises. The primary outcome was a diagnosis of AKP during the 14-week training program.

RESULTS

Forty-six participants (3.1%; 95% confidence interval [CI], 2.3-4.1) were diagnosed with AKP. There were 36 (4.8%; 95%CI, 3.5-6.7) new cases of AKP in the control group and 10 (1.3%; 0.7-2.4) in the intervention group. There was a 75% reduction in AKP risk in the intervention group (unadjusted hazard ratio = 0.25; 95% CI, 0.13-0.52; P < .001). Three participants (0.4%) from the intervention group were discharged from the military for medical reasons compared to 25 (3.4%) in the control group.

CONCLUSION

A simple set of lower limb stretching and strengthening exercises resulted in a substantial and safe reduction in the incidence of AKP in a young military population undertaking a physical conditioning program. Such exercises could also be beneficial for preventing this common injury among nonmilitary participants in recreational physical activity.

The potential neural mechanisms of acute indirect vibration

There is strong evidence to suggest that acute indirect vibration acts on muscle to enhance force, power, flexibility, balance and proprioception suggesting neural enhancement. Nevertheless, the neural mechanism(s) of vibration and its potentiating effect have received little attention. One proposal suggests that spinal reflexes enhance muscle contraction through a reflex activity known as tonic vibration stretch reflex (TVR), which increases muscle activation. However, TVR is based on direct, brief, and high frequency vibration (>100 Hz) which differs to indirect vibration, which is applied to the whole body or body parts at lower vibration frequency (5-45 Hz). Likewise, muscle tuning and neuromuscular aspects are other candidate mechanisms used to explain the vibration phenomenon. But there is much debate in terms of identifying which neural mechanism(s) are responsible for acute vibration; due to a number of studies using various vibration testing protocols. These protocols include: different methods of application, vibration variables, training duration, exercise types and a range of population groups. Therefore, the neural mechanism of acute vibration remain equivocal, but spinal reflexes, muscle tuning and neuromuscular aspects are all viable factors that may contribute in different ways to increasing muscular performance. Additional research is encouraged to determine which neural mechanism(s) and their contributions are responsible for acute vibration. Testing variables and vibration applications need to be standardised before reaching a consensus on which neural mechanism(s) occur during and post-vibration. Key pointsThere is strong evidence to suggest that acute indirect vibration acts on muscle to enhance force, power, flexibility, balance and proprioception, but little attention has been given to the neural mechanism(s) of acute indirect vibration.Current findings suggest that acute vibration exposure may cause a neural response, but there is little consensus on identifying which neural mechanism(s) are specifically responsible. This is due to a number of studies using various vibration testing protocols (i.e.varying frequencies, amplitudes, durations, and methods of application).Spinal reflexes, muscle tuning and neuromuscular aspects and central motor command are all viable neuromechanical factors that may contribute at different stages to transiently increasing muscular performance.Additional research is encouraged to determine when (pre, during and post) the different neural mechanism(s) respond to direct and indirect vibration stimuli.

Neuromuscular Responses to Platform Perturbations in Power-Versus Endurance-Trained Athletes

The purpose was to assess differences in postural response characteristics between two groups of elite athletes having power or endurance training. Participants were all men and included power- ( M age = 21 yr., SD = 3, n = 12) and endurance-trained ( M age = 22, SD = 3, n = 12) athletes. Muscle response characteristics and center of pressure measures were recorded during recovery from Fast (10 cm at 80 cm/sec.) and Slow (10 cm at 20 cm/sec.) horizontal platform perturbations. In response to Fast perturbations, power-trained athletes responded with significantly shorter times to stabilize the center of pressure, shorter muscle-contraction onset times, and larger muscle response amplitudes than endurance-trained athletes. This suggests power-trained athletes are more effective than endurance-trained athletes in responding to balance threats such as slips and trips in daily life and that power training should be studied to improve balance control of balance-impaired populations.

Bilateral neuromuscular plasticity from unilateral training of the ankle dorsiflexors

Training a muscle group in one limb yields strength gains bilaterally-the so-called cross-education effect. However, to date there has been little study of the targeted application of this phenomenon in a manner relevant to clinical rehabilitation. For example, it may be applicable post-stroke, where hemiparesis leads to ankle flexor weakness. The purpose of this study was to examine the effects of high-intensity unilateral dorsiflexion resistance training on agonist (tibialis anterior, TA) and antagonist (plantarflexor soleus, SOL) muscular strength and H-reflex excitability in the trained and untrained limbs. Ankle flexor and extensor torque, as well as SOL and TA H-reflexes evoked during low-level contraction, were measured before and after 5 weeks of dorsiflexion training (n = 19). As a result of the intervention, dorsiflexor maximal voluntary isometric contraction force (MVIC) significantly increased (P < 0.05) in both the trained and untrained limbs by 14.7 and 8.4%, respectively. No changes in plantarflexor MVIC force were observed in either limb. Significant changes in H-reflex excitability threshold were also detected: H(@thresh) significantly increased in the trained TA and SOL; and H(@max) decreased in both SOL muscles. These findings reveal that muscular crossed effects can be obtained in the ankle dorsiflexor muscles and provide novel information on agonist and antagonist spinal adaptations that accompany unilateral training. It is possible that the ability to strengthen the ankle dorsiflexors bilaterally could be applied in post-stroke rehabilitation, where ankle flexor weakness could be counteracted via dorsiflexor training in the less-affected limb.

Motor unit behavior during submaximal contractions following six weeks of either endurance or strength training

The study investigated changes in motor output and motor unit behavior following 6 wk of either strength or endurance training programs commonly used in conditioning and rehabilitation. Twenty-seven sedentary healthy men (age, 26.1 ± 3.9 yr; mean ± SD) were randomly assigned to strength training (ST; n = 9), endurance training (ET; n = 10), or a control group (CT; n = 8). Maximum voluntary contraction (MVC), time to task failure (isometric contraction at 30% MVC), and rate of force development (RFD) of the quadriceps were measured before ( week 0), during ( week 3), and after a training program of 6 wk. In each experimental session, surface and intramuscular EMG signals were recorded from the vastus medialis obliquus and vastus lateralis muscles during isometric knee extension at 10 and 30% MVC. After 6 wk of training, MVC and RFD increased in the ST group (17.5 ± 7.5 and 33.3 ± 15.9%, respectively; P < 0.05), whereas time to task failure was prolonged in the ET group (29.7 ± 13.4%; P < 0.05). The surface EMG amplitude at 30% MVC force increased with training in both groups, but the training-induced changes in motor unit discharge rates differed between groups. After endurance training, the motor unit discharge rate at 30% MVC decreased from 11.3 ± 1.3 to 10.1 ± 1.1 pulses per second (pps; P < 0.05) in the vasti muscles, whereas after strength training it increased from 11.4 ± 1.2 to 12.7 ± 1.3 pps ( P < 0.05). Finally, motor unit conduction velocity during the contractions at 30% MVC increased for both the ST and ET groups, but only after 6 wk of training ( P < 0.05). In conclusion, these strength and endurance training programs elicit opposite adjustments in motor unit discharge rates but similar changes in muscle fiber conduction velocity.

Effects of disinhibitory transcutaneous electrical nerve stimulation and therapeutic exercise on sagittal plane peak knee kinematics and kinetics in people with knee osteoarthritis during gait: a randomized controlled trial

Objective: To determine whether sensory transcutaneous electrical nerve stimulation (TENS) augmented with therapeutic exercise and worn for daily activities for four weeks would alter peak gait kinetics and kinematics, compared with placebo electrical stimulation and exercise, and exercise only.

Design: Randomized controlled trial.

Setting: Motion analysis laboratory.

Subjects: Thirty-six participants with radiographically assessed knee osteoarthritis and volitional quadriceps activation below 90% were randomly assigned to electrical stimulation, placebo and comparison (exercise-only) groups.

Interventions: Participants in all three groups completed a four-week quadriceps strengthening programme directed by an experienced rehabilitation clinician. Active electrical stimulation units and placebo units were worn in the electrical stimulation and placebo groups throughout the rehabilitation sessions as well as during all activities of daily living.

Main measures: Peak external knee flexion moment and angle during stance phase were analysed at a comfortable walking speed before and after the intervention.

Findings: Comfortable walking speed increased for all groups over time (TENS 1.16 ± 0.15 versus 1.32 ± 0.16 m/s; placebo 1.21 ± 0.34 versus 1.3 ± 0.24 m/s; comparison 1.27 ± 0.18 versus 1.5 ± 0.14 m/s), yet no group differences in speed were found. No differences were found for peak flexion moment or angle between groups overtime.

Conclusions: TENS in conjunction with therapeutic exercise does not seem to affect peak flexion moment and angle during stance over a four-week period in participants with tibiofemoral osteoarthritis.

Improvements in dynamic plantar flexor strength after resistance training are associated with increased voluntary activation and V-to-M ratio

The aim of this study was to investigate if, and via what mechanisms, resistance training of the plantar flexor muscles affects voluntary activation during maximal voluntary eccentric and concentric muscle actions. Twenty healthy subjects were randomized into a resistance training group ( n = 9) or a passive control group ( n = 11). Training consisted of 15 sessions of unilateral mainly eccentric plantar flexor exercise over a 5-wk period. During pre- and posttraining testing, dynamic plantar flexor strength was measured and voluntary activation was calculated using the twitch interpolation technique. The soleus Hoffman reflex (H-reflex) was used to assess motoneurone excitability and presynaptic inhibition of Ia afferents, whereas the soleus V-wave was used to test for changes in both presynaptic inhibition of Ia afferents and supraspinal inputs to the motoneurone pool. H-reflexes, V-waves, supramaximal M-waves, and twitches were evoked as the foot was moved at 5°/s through an angle of 90° during passive ankle rotations (passive H-relexes and M-waves) and during maximal voluntary concentric and eccentric plantar flexions [maximal voluntary contraction (MVC) H-reflexes, M-waves, and V-waves]. Training induced significant improvements in plantar flexor strength and voluntary activation during both concentric and eccentric maximal voluntary actions. Soleus passive and MVC H-to-M ratios remained unchanged after training, whereas the soleus V-to-M ratio was increased during both concentric and eccentric contractions after training. No changes were found in the control group for any of the parameters. The enhanced voluntary strength could be attributed partly to an increase in voluntary activation induced by eccentric training. Since the passive and MVC H-to-M ratios remained unchanged, the increase in activation is probably not due to decreased presynaptic inhibition. The increased V-to-M ratio for both action types indicates that increased voluntary drive from supraspinal centers and/or modulation in afferents other than Ia afferents may have contributed to such an increase in voluntary activation.

A mathematical model of neuromuscular adaptation to resistance training and its application in a computer simulation of accommodating loads

A large corpus of data obtained by means of empirical study of neuromuscular adaptation is currently of limited use to athletes and their coaches. One of the reasons lies in the unclear direct practical utility of many individual trials. This paper introduces a mathematical model of adaptation to resistance training, which derives its elements from physiological fundamentals on the one side, and empirical findings on the other. The key element of the proposed model is what is here termed the athlete's capability profile. This is a generalization of length and velocity dependent force production characteristics of individual muscles, to an exercise with arbitrary biomechanics. The capability profile, a two-dimensional function over the capability plane, plays the central role in the proposed model of the training-adaptation feedback loop. Together with a dynamic model of resistance the capability profile is used in the model's predictive stage when exercise performance is simulated using a numerical approximation of differential equations of motion. Simulation results are used to infer the adaptational stimulus, which manifests itself through a fed back modification of the capability profile. It is shown how empirical evidence of exercise specificity can be formulated mathematically and integrated in this framework. A detailed description of the proposed model is followed by examples of its application-new insights into the effects of accommodating loading for powerlifting are demonstrated. This is followed by a discussion of the limitations of the proposed model and an overview of avenues for future work.

Resistive vibration exercise attenuates bone and muscle atrophy in 56 days of bed rest: biochemical markers of bone metabolism

During and after prolonged bed rest, changes in bone metabolic markers occur within 3 days. Resistive vibration exercise during bed rest impedes bone loss and restricts increases in bone resorption markers whilst increasing bone formation.

INTRODUCTION

To investigate the effectiveness of a resistive vibration exercise (RVE) countermeasure during prolonged bed rest using serum markers of bone metabolism and whole-body dual X-ray absorptiometry (DXA) as endpoints.

METHODS

Twenty healthy male subjects underwent 8 weeks of bed rest with 12 months follow-up. Ten subjects performed RVE. Blood drawings and DXA measures were conducted regularly during and after bed rest.

RESULTS

Bone resorption increased in the CTRL group with a less severe increase in the RVE group (p = 0.0004). Bone formation markers increased in the RVE group but decreased marginally in the CTRL group (p < 0.0001). At the end of bed rest, the CTRL group showed significant loss in leg bone mass (-1.8(0.9)%, p = 0.042) whereas the RVE group did not (-0.7(0.8)%, p = 0.405) although the difference between the groups was not significant (p = 0.12).

CONCLUSIONS

The results suggest the countermeasure restricts increases in bone resorption, increased bone formation, and reduced bone loss during bed rest.

Resistance training induces supraspinal adaptations: evidence from movement-related cortical potentials

Early effects of a resistance training program include neural adaptations at multiple levels of the neuraxis, but direct evidence of central changes is lacking. Plasticity exhibited by multiple supraspinal centers following training may alter slow negative electroencephalographic activity, referred to as movement-related cortical potentials (MRCP). The purpose of this study was to determine whether MRCPs are altered in response to resistance training. Eleven healthy participants (24.6 +/- 3.5 years) performed 3 weeks of explosive unilateral leg extensor resistance training. MRCP were assessed during 60 self-paced leg extensions against a constant nominal load before and after training. Resistance training was effective (P < 0.001) in increasing leg extensor peak force (+22%), rate of force production (+32%) as well as muscle activity (iEMG; +47%, P < 0.05). These changes were accompanied by several MRCP effects. Following training, MRCP amplitude was attenuated at several scalp sites overlying motor-related cortical areas (P < 0.05), and the onset of MRCP at the vertex was 28% (561 ms) earlier. In conclusion, the 3-week training protocol in the present study elicited significant strength gains which were accompanied by neural adaptations at the level of the cortex. We interpret our findings of attenuated cortical demand for submaximal voluntary movement as evidence for enhanced neural economy as a result of resistance training.

Sarcopenia--mechanisms and treatments

BACKGROUND

Sarcopenia is a consequence of aging. This atrophic event is responsible for decrease in strength and associated functional deficits seen in the aging adult.

PURPOSE

This paper reviews: (1) the mechanisms contributing to sarcopenia, (2) the impact of age-related changes in muscle composition on 3 processes integral to muscle function, (3) the efficacy of pharmaceuticals and over-the-counter nutritional supplements in the management of sarcopenia, (4) experimental use of pharmaceutical regulation of myostatin to increase muscle mass and strength in animal models, and (5) efficacy of resistance training as a means of maintaining or recovering muscle mass and strength.

METHODS

PubMed was searched for relevant research articles using the following descriptors: sarcopenia, aging, muscle mass, muscle performance, muscle strength, myostatin, testosterone, growth hormone, dehydroepiandrosterone, hormone replacement, nutrition, resistance training, and endurance training.

RESULTS

Sarcopenia is mediated by multiple mechanisms, including alpha-motor neuron death, altered hormone concentrations, increased inflammation, and altered nutritional status. Age-related changes within muscle likely affect processes integral to muscle function. These changes negatively influence muscle performance directly or by contributing to sarcopenia. Pharmaceutical or supplement interventions to treat sarcopenia have not proved encouraging to date, either lacking or providing limited efficacy, along with the potential for negative health consequences. In contrast, resistance training has proven safe and highly effective for increasing muscle mass and strength in aging adults.

CONCLUSION

Sarcopenia is a multifactorial consequence of aging that will affect many adults. Resistance training is the most effective and safe intervention to attenuate or recover some of the loss of muscle mass and strength that accompanies aging.

Comparison between linear and daily undulating periodized resistance training to increase strength

To determine the most effective periodization model for strength and hypertrophy is an important step for strength and conditioning professionals. The aim of this study was to compare the effects of linear (LP) and daily undulating periodized (DUP) resistance training on body composition and maximal strength levels. Forty men aged 21.5 +/- 8.3 and with a minimum 1-year strength training experience were assigned to an LP (n = 20) or DUP group (n = 20). Subjects were tested for maximal strength in bench press, leg press 45 degrees, and arm curl (1 repetition maximum [RM]) at baseline (T1), after 8 weeks (T2), and after 12 weeks of training (T3). Increases of 18.2 and 25.08% in bench press 1 RM were observed for LP and DUP groups in T3 compared with T1, respectively (p < or = 0.05). In leg press 45 degrees , LP group exhibited an increase of 24.71% and DUP of 40.61% at T3 compared with T1. Additionally, DUP showed an increase of 12.23% at T2 compared with T1 and 25.48% at T3 compared with T2. For the arm curl exercise, LP group increased 14.15% and DUP 23.53% at T3 when compared with T1. An increase of 20% was also found at T2 when compared with T1, for DUP. Although the DUP group increased strength the most in all exercises, no statistical differences were found between groups. In conclusion, undulating periodized strength training induced higher increases in maximal strength than the linear model in strength-trained men. For maximizing strength increases, daily intensity and volume variations were more effective than weekly variations.

Seventy-year-old habitual volleyball players have larger tibial cross-sectional area and may be differentiated from their age-matched peers by the osteogenic index in dynamic performance

The osteogenicity of a given exercise may be estimated by calculating an osteogenic index (OI) consisting of magnitude and rate of strain. Volleyball involves repetitive jumping and requires high power output and thus may be expected to be beneficial to bone and performance. The purpose of the present study was to examine if habitual volleyball playing is reflected in OI. Ten elderly habitual volleyball players [age 69.9 (SD 4.4) years] and ten matched controls volunteered [age 69.7 (4.2) years] as subjects. Distal tibia (d), tibial mid-shaft (50) and femoral neck (FN) bone characteristics were measured using pQCT and DXA. To estimate skeletal rigidity, cross-sectional area (ToA(50)), and compressive (BSI(d)) and bending strength indices (SSImax(50)) were calculated. Maximal performance was assessed with eccentric ankle plantar flexion, isometric leg press and countermovement jump (CMJ). A fast Fourier transform (FFT) was calculated from the acceleration of the center of mass during the CMJ. Maximal acceleration (MAG) and mean magnitude frequency (MMF) were selected to represent the constituents of OI. OI was calculated as the sum of the products of magnitudes and corresponding frequencies. Volleyball players had 7% larger ToA(50) and 37% higher power in CMJ, 15% higher MAG and 36% higher OI (P <or= 0.047) than the matched controls. No difference was observed in leg press, plantar flexion or the MMF (P >or= 0.646). In conclusion, habitual volleyball players may be differentiated from their matched peers by their dynamic jumping performance, and the differences are reflected in the magnitude but not rate of loading.

The effect of strength training and short-term detraining on maximum force and the rate of force development of older men

This study examined the effect of strength training (ST) and short-term detraining on maximum force and rate of force development (RFD) in previously sedentary, healthy older men. Twenty-four older men (70-80 years) were randomly assigned to a ST group (n = 12) and C group (control, n = 12). Training consisted of three sets of six to ten repetitions on an incline squat at 70-90% of one repetition maximum three times per week for 16 weeks followed by 4 weeks of detraining. Regional muscle mass was assessed before and after training by dual-energy X-ray absorptiometry. Training increased RFD, maximum bilateral isometric force, and force in 500 ms, upper leg muscle mass and strength above pre-training values (14, 25, 22, 7, 90%, respectively; P < 0.05). After 4 weeks detraining all neuromuscular variables were significantly (P < 0.05) lower than after 16 weeks training but remained significantly (P < 0.05) higher than pre-training levels except for RFD which had returned to pre-training levels. These findings demonstrate that high-intensity ST can improve maximum force and RFD of older men. However, older individuals may lose some neuromuscular performance after a period of short-term detraining and that resistance exercise should be performed on a regular basis to maintain training adaptations.

Bilateral movement therapy post-stroke: underlying mechanisms and review

Aims

Up to 66% of individuals with stroke never regain functional use of their upper extremities. Bilateral movement training (BMT) is a task-specific rehabilitation technique that has recently been investigated for its influence on upper extremity recovery in individuals post-stroke. BMT is thought to affect the hemiparetic upper extremity by a phenomenon referred to as cross education, or the cross transfer effect.

Methods

This article reviews the theoretical accounts underlying the cross transfer effect and explain the means by which BMT may facilitate recovery of function in the hemiparetic arm. The current research evidence supporting the use of BMT as a therapeutic approach to stroke rehabilitation is discussed, and implications for clinical practice and recommendations for further research are presented.

Findings

Evidence is emerging that BMT improves impairments and function in people with hemiparesis after stroke. The main limitations of existing research on BMT include small sample sizes, varying initial impairment levels, and lack of control groups.

Conclusions

Future research needs to establish which individuals are most likely to benefi tfrom BMT, as well as the optimal dose of BMT, and whether BMT can be used as an adjunct to existing rehabilitation approaches for upper extremity rehabilitation.

Influence of motor unit synchronization on amplitude characteristics of surface and intramuscularly recorded EMG signals

The increase in muscle strength without noticeable hypertrophic adaptations is very important in some sports. Motor unit (MU) synchronisation and higher rate of MU activation are proposed as possible mechanisms for such a strength and electromyogram (EMG) increase in the early phase of a training regimen. Root mean square and/or integrated EMG are amplitude measures commonly used to estimate the adaptive changes in efferent neural drive. EMG amplitude characteristics could change also because of alteration in intracellular action potential (IAP) spatial profile. We simulated MUs synchronization under different length of the IAP profile. Different synchronization was simulated by variation of the percent of discharges in a referent MU, to which a variable percent of remaining MUs was synchronized. Population synchrony index estimated the degree of MU synchronization in EMG signals. We demonstrate that the increase in amplitude characteristics due to MU synchronization is stronger in surface than in intramuscularly detected EMG signals. However, the effect of IAP profile lengthening on surface detected EMG signals could be much stronger than that of MU synchronization. Thus, changes in amplitude characteristics of surface detected EMG signals with progressive strength training could hardly be used as an indicator of changes in neural drive without testing possible changes in IAPs.

Força muscular versus pressão arterial de repouso: uma revisão baseada no treinamento com pesos

INTRODUÇÃO: O exercício com pesos é atualmente recomendado para diferentes grupos de indivíduos. Seu principal objetivo é o aumento na força muscular, mas podem ocorrer outros resultados , como a redução na pressão arterial (PA) de repouso. Contudo, é pouco abordada a relação entre prescrição do treinamento com pesos, aumento da força e comportamento da PA de repouso em humanos. OBJETIVO: Analisar a PA após uma sessão aguda de exercícios com pesos e após um período de treinamento com pesos, em indivíduos normotensos e hipertensos, em estudos publicados na literatura internacional. MÉTODOS: As referências foram selecionadas de três formas distintas: 1) para compor as sugestões de treinamento de pesos foi utilizado um estudo meta-analítico e um posicionamento oficial de uma reconhecida entidade de pesquisa; 2) para os dados do exercício com pesos e PA de repouso nos momentos pós-exercício, foram pesquisados estudos na base Medline publicados em inglês que acompanharam a PA por pelo menos 60 min; 3) as referências sobre treinamento com pesos em longo prazo e PA de repouso foram resgatadas do último estudo meta-analítico sobre o tema, adicionadas dos experimentos publicados até julho de 2008. RESULTADOS: Após analisar as referências, a prescrição do treinamento com pesos, na maioria dos estudos, seguiu sugestões atuais. Porém, somente em poucos estudos a PA de repouso foi reduzida, tanto em normotensos quanto em hipertensos. CONCLUSÕES: Mesmo com certa variação na prescrição, o treinamento com pesos parece ser suficiente para aumentar a força muscular. Contudo, ainda faltam pesquisas para inferir sobre sua relação com a PA de repouso de normotensos e hipertensos.

Elderly women have blunted response to resistance training despite reduced antagonist coactivation

PURPOSE

To test the ability of a combination high-velocity/high-resistance training program to enhance knee extensor muscle strength, power, nervous activation of muscle, and muscle activation time in inactive women and compare the response to training between young and old women.

METHODS

The study involved 49 inactive women, with young (18-33 yr, n = 25) and old (65-84 yr, n = 24) distributed to training and control groups using blocked randomization. Electrically evoked muscle twitches were measured for the knee extensors; then maximal, voluntary, isometric knee extensions were performed in a visually cued reaction time (RT) task, followed by 8 wk of explosive resistance training.

RESULTS

Training increased peak torque (+12%, P = 0.03) and reduced antagonist coactivation (-13%, P = 0.02) similarly for both age groups. Young training group increased the rate of torque development by 34% compared to young controls (-7%), old training (+9%), and old controls (+8%) (P = 0.002). Young training group increased impulse by 53%, which was greater than young controls (-11%), old training (+12%), and old controls (+9%) (P = 0.001). Resistance training did not change electrically evoked twitch, RT (premotor time, motor time, or reaction time), or nervous activation measures (onset EMG amplitude or rate of EMG rise).

CONCLUSIONS

Explosive force training was ineffective at enhancing muscle twitch characteristics, neural drive, or RT in young or old women. It did enhance peak muscle force in both young and old, modulated through a reduction in antagonist coactivation. Older participants showed less of an improvement in the rate of torque development and contractile impulse than young, indicating either that this sample of older women had a reduced capacity to develop muscle power or that the 8-wk isokinetic resistance training program used in this study was not a sufficient stimulus for adaptation.

The effect of additional strengthening of hip abductor and lateral rotator muscles in patellofemoral pain syndrome: a randomized controlled pilot study

OBJECTIVES

To study the effect of additional strengthening of hip abductor and lateral rotator muscles in a strengthening quadriceps exercise rehabilitation programme for patients with the patellofemoral pain syndrome.

DESIGN

Randomized controlled pilot trial.

SETTING

Clinical setting with home programme.

PARTICIPANTS

Fourteen patients with patellofemoral pain syndrome.

INTERVENTION

The subjects were randomly assigned to the intervention group (strengthening of quadriceps plus strengthening of hip abductor and lateral rotator muscles) or to the control group (strengthening of quadriceps). Both groups participated in a six-week home exercise protocol.

MAIN OUTCOME MEASURES

The perceived pain symptoms, isokinetic eccentric knee extensor, hip abductor and lateral rotator torques and the gluteus medius electromyographic activity were assessed before and after treatment. Parametric and non-parametric tests were used to compare the groups before and after treatment with alpha=0.05.

RESULTS

Only the intervention group improved perceived pain symptoms during functional activities (P=0.02-0.04) and also increased their gluteus medius electromyographic activity during isometric voluntary contraction (P=0.03). Eccentric knee extensors torque increased in both groups (P=0.04 and P=0.02). There was no statistically significant difference in the hip muscles torque in either group.

CONCLUSION

Supplementation of strengthening of hip abductor and lateral rotator muscles in a strengthening quadriceps exercise programme provided additional benefits with respect to the perceived pain symptoms during functional activities in patients with patellofemoral pain syndrome after six weeks of treatment.

Interpretation of EMG integral or RMS and estimates of "neuromuscular efficiency" can be misleading in fatiguing contraction

In occupational and sports physiology, reduction of neuromuscular efficiency (NME) and elevation of amplitude characteristics, such as root mean square (RMS) or integral of surface electromyographic (EMG) signals detected during fatiguing submaximal contraction are often related to changes in neural drive. However, there is data showing changes in the EMG integral (I(EMG)) and RMS due to peripheral factors. Causes for these changes are not fully understood. On the basis of computer simulation, we demonstrate that lengthening of intracellular action potential (IAP) profile typical for fatiguing contraction could affect EMG amplitude characteristics stronger than alteration in neural drive (central factors) defined by number of active motor units (MUs) and their firing rates. Thus, relation of these EMG amplitude characteristics only to central mechanisms can be misleading. It was also found that to discriminate between changes in RMS or I(EMG) due to alterations in neural drive from changes due to alterations in peripheral factors it is better to normalize RMS of EMG signals to the RMS of M-wave. In massive muscles, such normalization is more appropriate than normalization to either peak-to-peak amplitude or area of M-wave proposed in literature.

(Over)training effects on quantitative electromyography and muscle enzyme activities in standardbred horses

Too intensive training may lead to overreaching or overtraining. To study whether quantitative needle electromyography (QEMG) is more sensitive to detect training (mal)adaptation than muscle enzyme activities, 12 standardbred geldings trained for 32 wk in age-, breed-, and sex-matched fixed pairs. After a habituation and normal training (NT) phase ( phases 1 and 2, 4 and 18 wk, respectively), with increasing intensity and duration and frequency of training sessions, an intensified training (IT) group ( phase 3, 6 wk) and a control group (which continued training as in the last week of phase 2) were formed. Thereafter, all horses entered a reduced training phase ( phase 4, 4 wk). One hour before a standardized exercise test (SET; treadmill), QEMG analysis and biochemical enzyme activity were performed in muscle or in biopsies from vastus lateralis and pectoralis descendens muscle in order to identify causes of changes in exercise performance and eventual (mal)adaptation in skeletal muscle. NT resulted in a significant adaptation of QEMG parameters, whereas in muscle biopsies hexokinase activity was significantly decreased. Compared with NT controls, IT induced a stronger adaptation (e.g., higher amplitude, shorter duration, and fewer turns) in QEMG variables resembling potentially synchronization of individual motor unit fiber action potentials. Despite a 19% decrease in performance of the SET after IT, enzyme activities of 3-hydroxyacyl dehydrogenase and citrate synthase displayed similar increases in control and IT animals. We conclude that 1) QEMG analysis is a more sensitive tool to monitor training adaptation than muscle enzyme activities but does not discriminate between overreaching and normal training adaptations at this training level and 2) the decreased performance as noted in this study after IT originates most likely from a central (brain) rather than peripheral level.

Chronic low-frequency rTMS of primary motor cortex diminishes exercise training-induced gains in maximal voluntary force in humans

Although there is consensus that the central nervous system mediates the increases in maximal voluntary force (maximal voluntary contraction, MVC) produced by resistance exercise, the involvement of the primary motor cortex (M1) in these processes remains controversial. We hypothesized that 1-Hz repetitive transcranial magnetic stimulation (rTMS) of M1 during resistance training would diminish strength gains. Forty subjects were divided equally into five groups. Subjects voluntarily (Vol) abducted the first dorsal interosseus (FDI) (5 bouts x 10 repetitions, 10 sessions, 4 wk) at 70-80% MVC. Another group also exercised but in the 1-min-long interbout rest intervals they received rTMS [Vol+rTMS, 1 Hz, FDI motor area, 300 pulses/session, 120% of the resting motor threshold (rMT)]. The third group also exercised and received sham rTMS (Vol+Sham). The fourth group received only rTMS (rTMS_only). The 37.5% and 33.3% gains in MVC in Vol and Vol+Sham groups, respectively, were greater (P = 0.001) than the 18.9% gain in Vol+rTMS, 1.9% in rTMS_only, and 2.6% in unexercised control subjects who received no stimulation. Acutely, within sessions 5 and 10, single-pulse TMS revealed that motor-evoked potential size and recruitment curve slopes were reduced in Vol+rTMS and rTMS_only groups and accumulated to chronic reductions by session 10. There were no changes in rMT, maximum compound action potential amplitude (M(max)), and peripherally evoked twitch forces in the trained FDI and the untrained abductor digiti minimi. Although contributions from spinal sources cannot be excluded, the data suggest that M1 may play a role in mediating neural adaptations to strength training.

Detraining and retraining in older adults following long-term muscle power or muscle strength specific training

BACKGROUND

Training cessation among older adults is associated with the loss of functional ability. However, exercise programs undertaken prior to activity cessation may offer functional protection. In the present study, the residual effects of muscle power or muscle strength training were investigated following extended detraining and subsequent retraining.

METHODS

Thirty-eight healthy independent older adults (65-84 years) entered a 24-week detraining period subsequent to 24 weeks of training. Following detraining, participants recommenced training using either the high-velocity muscle power (HV) or muscle strength (ST) protocol, as undertaken during the initial training period, twice weekly for 12 weeks. Isometric and dynamic muscle strength, muscle power, movement velocity, muscle endurance, electromyographic activity, and the results of a battery of functional performance tasks were assessed.

RESULTS

Muscle function and functional performance increased following initial training, however, no group differences were observed. Detraining resulted in similar declines in muscle power and muscle strength for both groups (p <.05) (power, HV 17.8 +/- 1.8%, ST 15.5 +/- 2.2%; and strength, HV 17.1 +/- 2.2%, ST 16.5 +/- 1.8%), with comparable accrual following retraining. No significant changes in functional ability were observed following detraining (average change; HV 3.1 +/- 3.5% and ST 2.1 +/- 3.5%) or retraining. No group differences emerged in this study.

CONCLUSION

Cessation of training resulted in only a modest loss of muscle power and strength that was recouped following 12 weeks of retraining. Importantly, training-induced gains in functional performance were preserved during detraining. The residual effects of power or strength training appear comparable, and both may be suitable exercise modes prior to a period of activity cessation to promote physical independence.