Can continuous physical training counteract aging effect on myoelectric fatigue? A surface electromyography study application

Repeated practice runs during on-snow training do not generate any measurable neuromuscular alterations in elite alpine skiers

Background

Alpine skiers typically train using repeated practice runs requiring high bursts of muscle activity but there is little field-based evidence characterizing neuromuscular function across successive runs.

Purpose

To examine the impact of repeated ski runs on electromyographic activity (EMG) of the knee extensors and flexors in elite alpine skiers.

Methods

Nineteen national team alpine skiers were tested during regular ski training [Slalom (SL), Giant Slalom (GS), Super Giant Slalom and Downhill (Speed)] for a total of 39 training sessions. The surface EMG of the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and semimembranosus/semitendinosus (SMST) muscles was continuously recorded along with right knee and hip angles. The EMG root mean square signal was normalized to a maximal voluntary contraction (%MVC). The first and fourth runs of the training session were compared.

Results

There was no meaningful main effect of run on EMG relative activation time or mean power frequency beyond the skier's intrinsic variability. However, EMG activity of the vastii increased from the first to the fourth run in SL [VM, ~+3%MVC for IL and outside leg (OL), p = 0.035)], speed (VL, IL:+6%/OL:+11%, p = 0.015), and GS (VM, IL:0/OL:+7%, p < 0.001); the later with an interaction with leg (p < 0.001) due to a localized increase on the OL. The run time and turn time did not change from the first to the fourth run. There were no meaningful changes in angular velocities, amplitude of movement, or maximal and minimal angles.

Conclusion

Neuromuscular activity remains highly stable in elite skiers with low variability across four runs.

Is fatigue a muscular phenomenon in Parkinson's disease? Implications for rehabilitation

BACKGROUND

Fatigue in Parkinson's Disease (PD) compromises patients' physical activity and poses questions on how to plan correct rehabilitation training. In addition, the relationship between subjective perceived fatigue and fatigue in motor performance is not yet entirely understood. As a consequence, a conclusive interpretation of muscular mechanisms of fatigue in PD has not yet been achieved. Among the various instrumental evaluations for fatigue, multichannel surface electromyography (sEMG) is a recognized tool that permits the study of myoelectric manifestations of fatigue.

AIM

To assess if muscles in PD show a different myoelectric fatigue pattern compared to the muscles of healthy age-matched subjects.

DESIGN

Observational controlled study.

POPULATION

Idiopathic Parkinson's Disease, Hohen &Yahr II and III stage, Parkinsonian Fatigue Scale average score ≥ 2.95, no therapy modification in the 4 weeks preceding the study; exclusion criteria: Mini Mental State Examination ≤ 24, upper limb disease/symptoms that might interfere with sEMG analysis, presence of other fatiguerelated conditions. Twenty patients were selected according to these criteria. Twenty untrained healthy subjects were matched.

METHODS

All subjects underwent a muscle fatigue protocol and a sEMG analysis of the right biceps brachii muscle during electrically stimulated and voluntary contractions in order to obtain a myoelectric fatigue muscular pattern. The myoelectric pattern is characterized by the modifications of the following sEMG variables: reduction of mean frequency and muscle fibre conduction velocity, increase of average rectified value.

RESULTS

No statistical differences where observed between groups for sEMG variables and muscular electric behaviour in all contraction conditions (all p> .05).

CONCLUSIONS

Our results show that parkinsonian muscles does not differ from the muscles of healthy age-matched subjects in developing peripheral myoelectric fatigue. Nevertheless, the role of fatigue perception at rest and particularly during physical activity must be clearly understood in order to further target the rehabilitative approach for fatigued parkinsonian patients and to reduce hypomobility.

CLINICAL REHABILITATION IMPACT

In rehabilitative terms, these findings allow us to highlight the possibility of performing sustained training with isometric contractions in PD subjects; therefore, fatigue "per se" does not constitute a barrier for the execution of muscular exercises, likewise intensive.

Hand rest and wrist support are effective in preventing fatigue during prolonged typing

STUDY DESIGN

Case series (longitudinal).

INTRODUCTION

Only few reports concerning the efficacy of commonly used strategies for preventing upper limb occupational disorders associated with prolonged typing exist.

PURPOSE OF THE STUDY

We aimed to investigate whether the duration of typing and the use of 2 strategies (hand rest and wrist support) changes muscle physiological response and therefore the electromyography records.

METHODS

We enrolled 25 volunteers, who were unfamiliar with the task and did not have musculoskeletal disorders. The subjects underwent 3 prolonged typing protocols to investigate the efficacy of the 2 adopted strategies in reducing the trapezius, biceps brachii, and extensor digitorum communis fatigue.

RESULTS

Typing for 1 hour induced muscular fatigue (60%-67% of the subjects). The extensor digitorum communis muscle exhibited the highest percentage of fatigue (72%-84%) after 1 and 4 hours of typing (1 hour, P = .04; 4 hours, P = .02). Fatigue levels in this muscle were significantly reduced (24%) with the use of pause typing (4 hours, P = .045), whereas biceps brachii muscle fatigue was reduced (32%) only with the use of wrist supports (P = .02, after 4 hours). Trapezius muscle fatigue was unaffected by the tested occupational strategies (1 hour, P = .62; 4 hours, P = .85).

DISCUSSION

Despite presenting an overall tendency for fatigue detected during the application of the protocols, the assessed muscles exhibited different behavior patterns, depending on both the preventive strategy applied and the muscle mechanical role during the task.

CONCLUSION

Hand rest and wrist support can successfully reduce muscle fatigue in specific upper limb muscles during prolonged typing, leading to a muscle-selective reduction in the occurrence of fatigue and thus provide direct evidence that they may prevent work-related musculoskeletal disorders.

LEVEL OF EVIDENCE

N/A.

Localized muscle vibration reverses quadriceps muscle hypotrophy and improves physical function: a clinical and electrophysiological study

Quadriceps weakness has been associated with knee osteoarthritis (OA). High-frequency localized muscle vibration (LMV) has been proposed recently for quadriceps strengthening in patients with knee OA. The purpose of this study was (a) to investigate the clinical effectiveness of high-frequency LMV on quadriceps muscle in patients with knee OA and (b) to disentangle, by means of surface electromyography (sEMG), the underlying mechanism. Thirty patients, aged between 40 and 65 years, and clinically diagnosed with knee OA were included in this randomized, controlled, single-blinded pilot study. Participants were randomly assigned to two groups: a study group treated with LMV, specifically set for muscle strengthening (150 Hz), by means of a commercial device VIBRA, and a control group treated with neuromuscular electrical stimulation. Clinical outcome was measured using the Western Ontario and McMaster Universities Osteoarthritis Index, Visual Analogue Scale, knee range of motion, Timed Up and Go test, and Stair climbing test. To assess changes in muscle activation and fatigue a subgroup of 20 patients was studied with the use of sEMG during a sustained isometric contraction. The LMV group showed a significant change in Western Ontario and McMaster Universities Osteoarthritis Index score, Visual Analogue Scale score, Timed Up and Go test, Stair Climbing Test, and knee flexion. These improvements were not significant in patients treated with neuromuscular electrical stimulation. sEMG analysis suggested an increased involvement of type II muscle fibers in the group treated with LMV. In conclusion, the present study supports the effectiveness of local vibration in muscle function and clinical improvement of patients with knee OA.

Fatigue and fibromyalgia syndrome: clinical and neurophysiologic pattern

The concept of 'fatigue' is strictly related to parameters of the setting in which fatigue is measured. Therefore, it is mandatory to provide a definition of fatigue and the modalities of its use. This is of pivotal importance with regard to the fibromyalgia (FM) syndrome, where fatigue is the most invalidating symptom and where, paradoxically, no clear and widely accepted definition of fatigue is available in the literature as yet. In the clinical setting, fatigue can be measured by different methods of various complexity. The simplest technique to assess fatigue involves the use of a visual analogue scale (VAS); however, a number of scales with differing levels of complexity are available for use. It is, often, difficult to detach the term 'fatigue' from tiredness and task failure, which correspond to two completely distinguished forms of fatigue: one with central origin (tiredness) and another which is localised within the muscle (peripheral muscle fatigue). The former is related to changes in motor-unit-recruitment strategies, whereas the latter is attributed to changes in membrane properties. To extensively assess fatigue and, partially, to avoid confusion among the types of fatigue described above, a number of laboratory tests have been developed; among these, there are multichannel surface electromyography (EMG) recordings. Using this type of an approach, it is possible the estimation of motor unit location within the muscle, the decomposition of the surface EMG (sEMG) interference signal into constituent trains of motor unit action potentials (MUAPs) and the analysis of single unit properties.

Prevention of falling risk in elderly people: the relevance of muscular strength and symmetry of lower limbs in postural stability

Falls are one of the major health problems affecting the quality of life among older adults. The aging process is associated with decreasing muscle strength and an increasing risk of falling. The variables and techniques adopted to quantify muscular strength and postural stability were different in each protocol; a great number of reports analyzed the risk factors and predictors of falls, but the results appear still uncertain. To date, there is no clear, definitive statement or review that has examined the effect of the quadriceps strength on static balance performances in different sensory conditions. This contribution aims to provide an overview of experimental works to increase the comprehension and prevention of falls and fall-related injuries in the elderly. Based on a review of the literature, this work was designed to explore the relationship among risk of falls, postural stability, and muscular strength of lower limbs in older adults.

Consequences of lower extremity and trunk muscle fatigue on balance and functional tasks in older people: a systematic literature review

Background

Muscle fatigue reduces muscle strength and balance control in young people. It is not clear whether fatigue resistance seen in older persons leads to different effects. In order to understand whether muscle fatigue may increase fall risk in older persons, a systematic literature review aimed to summarize knowledge on the effects of lower extremity and trunk muscle fatigue on balance and functional tasks in older people was performed.

Methods

Studies were identified with searches of the PUBMED and SCOPUS data bases.

Papers describing effects of lower extremity or trunk muscle fatigue protocols on balance or functional tasks in older people were included. Studies were compared with regards to study population characteristics, fatigue protocol, and balance and functional task outcomes.

Results

Seven out of 266 studies met the inclusion criteria. Primary findings were: fatigue via resistance exercises to lower limb and trunk muscles induces postural instability during quiet standing; induced hip, knee and ankle muscle fatigue impairs functional reach, reduces the speed and power of sit-to-stand repetitions, and produces less stable and more variable walking patterns; effects of age on degree of fatigue and rate of recovery from fatigue are inconsistent across studies, with these disparities likely due to differences in the fatigue protocols, study populations and outcome measures.

Conclusion

Taken together, the findings suggest that balance and functional task performance are impaired with fatigue. Future studies should assess whether fatigue is related to increased risk of falling and whether exercise interventions may decrease fatigue effects.

Physical work capacity in older adults: implications for the aging worker

BACKGROUND

In many developed countries, the workforce is rapidly aging. Occupational demands however, have not decreased despite the fact that workers see a decline in physical work capacity with age. The purpose of this review is to examine the physiological adaptations to aging, the impact of aging on performance and the benefits of physical fitness in improving functional work capacity in aging individuals.

METHODS

An extensive search of the scientific literature was performed, acquiring published articles which examined the physiological changes associated with age-related decrements in the physical work capacity of healthy aging adults. The databases accessed included AARP Ageline, AccessScience, Annual Reviews, CISTI, Cochrane Library, Clinical Evidence, Digital Dissertations (Proquest), Embase, HealthSTAR, Medline, PubMed, Scopus, and PASCAL and included relevant information sites obtained on the world wide web.

RESULTS

While a great deal of variation exists, an average decline of 20% in physical work capacity has been reported between the ages of 40 and 60 years, due to decreases in aerobic and musculoskeletal capacity. These declines can contribute to decreased work capacity, and consequential increases in work-related injuries and illness. However, differences in habitual physical activity will greatly influence the variability seen in individual physical work capacity and its components. Well-organized, management-supported, work-site health interventions encouraging physical activity during work hours could potentially decrease the incidence of age-related injury and illness.

CONCLUSIONS

Age-associated functional declines and the accompanying risk of work-related injury can be prevented or at least delayed by the practice of regular physical activity. Older workers could optimally pursue their careers until retirement if they continuously maintain their physical training.

Mechanical and EMG responses of the vastus lateralis and changes in biochemical variables to isokinetic exercise in endurance and power athletes

Twelve endurance athletes and six power athletes performed fatiguing isokinetic knee flexions/extensions. Isokinetic torque was recorded during the exercise. Isometric torque, cortisol and lactate responses, electromyographic (EMG) mean power frequency, average rectified value, and conduction velocity were analysed before and after the isokinetic exercise to determine correlations between electrophysiological variables and mechanical performances and/or blood concentrations of biomarkers in the two groups of athletes. The EMG variables were estimated from signals recorded from the vastus lateralis in both voluntary and electrically elicited isometric contractions. Power athletes recorded higher values than endurance athletes for the following variables: pre-exercise isometric maximal voluntary contraction (MVC), isokinetic MVC, rate of mechanical fatigue during isokinetic contractions, pre - post exercise variations and recovery times of conduction velocity and mean power frequency, and lactate concentrations. Moreover, conduction velocity overshooting was observed in endurance athletes during the recovery phase after exercise. The correlation analyses showed that the higher the rate of mechanical fatigue, the higher the lactate production and the reduction in conduction velocity due to the exercise.

A method for positioning electrodes during surface EMG recordings in lower limb muscles

PURPOSE

The aim of this work is to provide information about the degree of inter-subject uniformity of location of innervation zone (IZ) in 13 superficial muscles of the lower limb. The availability of such information will allow researchers to standardize and optimize their electrode positioning procedure and to obtain accurate and repeatable estimates of surface electromyography (sEMG) signal amplitude, spectral variables and muscle fiber conduction velocity.

METHODS

Surface EMG signals from gluteus maximus, gluteus medius, tensor faciae latae, biceps femoris, semitendinosus, vastus medialis obliquus, vastus lateralis, rectus femoris, tibialis anterior, peroneus longus, soleus, gastrocnemius medialis and lateralis muscles of ten healthy male subjects aged between 25 and 34 years (average = 29.2 years, S.D. = 2.5 years) were recorded to assess individual IZ location and signal quality.

RESULTS

Tensor faciae latae, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius medialis and lateralis showed a high level of both signal quality and IZ location uniformity. In contrast, rectus femoris, gluteus medius and peroneus longus were found to show poor results for both indexes. Gluteus maximus, vastus medialis obliquus and tibialis anterior were found to show high signal quality but low IZ location uniformity. Finally, soleus muscle was found to show low signal quality but high IZ location uniformity.

CONCLUSIONS

This study identifies optimal electrode sites for muscles in the lower extremity by providing a standard landmarking technique for the localization of the IZ of each muscle so that surface EMG electrodes can be properly positioned between the IZ and a tendon.