Jessica Elert

The influences of muscle fibre proportions and areas upon EMG during maximal dynamic knee extensions

Abstract This study is an investigation of the relationship between muscle morphology and surface electromyographic (EMG) parameters [mean frequency of the power spectrum (MNF), signal amplitude (root mean square, RMS) and the signal amplitude ratio (SAR; i.e. the ratio between the RMS level during the passive part of the contraction cycle and the RMS level during the active part of the contraction cycle)] during 100 maximal dynamic knee extensions at 90° · s−1. Each contraction cycle comprised of 1 s of active knee extension and 1 s of passive knee flexion. The surface EMG was recorded from the vastus lateralis muscle. Twenty clinically healthy subjects participated in the study, and muscle biopsy samples of the vastus lateralis were obtained from 19 of those subjects. The relationships between muscle morphology and EMG were investigated at three stages of the test: initially, during the fatigue phase (initial 40 contractions), and at the endurance level (the final 50 contractions). Major findings on correlations are that SAR and MNF tended to correlate positively with the proportion of type 1 fibres, and RMS correlated positively with the proportion of type 2 muscle fibres. The muscle fibre areas showed little correlation with the EMG variables under investigation. The results of the present study showed that the three EMG variables of a dynamic endurance test that were investigated (RMS, MNF and SAR) were clearly correlated with the proportions of the different fibre types, but only to a small extent with fibre areas. These findings contradict some of the theoretical models of the EMG, especially for parameters in the frequency domain.

Randomized Controlled Trial of Physiotherapy and Feldenkrais Interventions in Female Workers with Neck-Shoulder Complaints

The present study aimed to investigate whether physiotherapy or Feldenkrais interventions resulted in a reduction of complaints from the neck and shoulders (prevalence, pain intensity, sick leave, and disability in leisure and work roles) in 97 female industrial workers (not on long-term sick leave). Range of motion of neck and shoulders, VO2, endurance score (i.e., summation of pain intensity ratings during a static shoulder flexion), cortical control according to the Feldenkrais methodology, and physiological capacity according to a dynamic endurance test of the shoulder flexors with simultaneous surface EMG were also recorded. The workers were randomized to: (1) physiotherapy group (PT-group; treatment according to the ergonomic program of the PTs of the occupational health care service), (2) Feldenkrais group (F-group; education according to the Feldenkrais methodology), or (3) control group (C-group; no intervention). Pre- and post-tests were made at one-year intervals. The two interventions lasted 16 weeks during paid working time. The F-group showed significant decreases in complaints from neck and shoulders and in disability during leisure time. The two other groups showed no change (PT-group) or worsening of complaints (C-group). The present study showed significant positive changes in complaints after the Feldenkrais intervention but not after the physiotherapy intervention. Possible mechanisms behind the effects in the F-group are discussed.

Reproducibility of surface EMG variables and peak torque during three sets of ten dynamic contractions

The interpretation of the electromyogram (EMG) of dynamic contractions might be difficult because the movement per se introduces additional factors that could affect its characteristics. There is a lack of studies concerning the reproducibility of surface EMG registrations during dynamic contractions. The aim was to investigate the during-the-day reproducibility (using intra-class correlation; ICC) of the peak torque (PT) and the EMG variables (without removing the electrodes) of dynamic contractions. Ten healthy subjects performed three sets of 10 dynamic maximum right-knee extensions with a one-hour interval in between, using an isokinetic dynamometer and the PT was determined. EMG signals were recorded from the right vastus lateralis, rectus femoris and vastus medialis muscles using surface electrodes and the mean frequency of the power spectrum (MNF [Hz]) and the signal amplitude (RMS [microV]), were computed. The ability to relax in-between the maximum extensions was calculated as a ratio of the RMS during the passive flexion phase and the RMS during the active extension phase of each contraction cycle: the signal amplitude ratio (SAR). Both PT (ICC = 0.99) and RMS (ICC = 0.83-0.98) had good reproducibility. The reproducibility of MNF was good for all muscles when the mean of contraction nos.: 1-10 was used. Vastus lateralis had the highest ICC among the three muscles. The reproducibility of SAR was generally poor (ICC < 0.60). The present study showed good reproducibility for common EMG variables (MNF and RMS) obtained during maximum isokinetic contractions.

Mechanical performance and electromyography during repeated maximal isokinetic shoulder forward flexions in female cleaners with and without myalgia of the trapezius muscle and in healthy controls.

Abstract This cross-sectional study aimed at investigating the influence of occupational exposure to static and highly repetitive work involving the neck and shoulder muscles, myalgia of and tender point in the trapezius muscle on biomechanical output, and electromyogram (EMG) variables (mean frequency MNF, signal amplitude and ability to relax) during maximal forward flexions of the shoulder muscles. Groups of 25 cleaners suffering from chronic myalgia of the trapezius muscle, 25 cleaners free from myalgia of the trapezius muscle and 21 teachers performed 150 forward flexions using an isokinetic dynamometer. Perception of fatigue was reported and surface EMG was recorded from four muscles during the endurance test. The cleaners were stronger than the teachers. Myalgia was associated with lower levels of endurance and a high degree of perceived fatigue. The ability to relax the trapezius muscle decreased with age and was even lower in cleaners with and without myalgia. Higher MNF of the deltoid muscle but not of the trapezius muscle was found in the group suffering from myalgia compared to the groups free from myalgia. This cross-sectional study indicated that myalgia of the trapezius muscle did not influence the strength but did influence the endurance of the forward flexor muscles of cleaners. The observed decrease in the ability to relax the trapezius muscle in cleaners compared to healthy teachers might be indicative of a future insufficiency in the muscle. Prospective studies are needed to define the significance of the results presented here.

Effect of a general fitness program on musculoskeletal symptoms, clinical status, physiological capacity, and perceived work environment among home care service personnel

The aim of the present controlled study was to evaluate the effect of a general fitness program, performed by an occupational health service, using pre-post assessment for a number of different outcome measures. A total of 160 employees working in the central home care service district of Umeå, Sweden were asked to participate in a program of a 1-year long exercise program. Of the 160 selected, 54 subjects declined to participate and nine subjects were rejected after a medical check up. The remaining 97 subjects participated in a schedule consisting of pre-post medical and physiotherapy examinations, questionnaires concerning sociodemography, musculoskeletal and general health complaints and work environment, physiological tests of cardiovascular fitness, and of strength and endurance of shoulder flexors and knee extensors, and registration of sick leave. The subjects were randomly assigned to an exercise (treatment) or control group. The exercise group trained twice a week for 1 year using a mixed program including exercises for coordination, strength/endurance, and fitness. The test schedule was repeated for both groups after 1 year. The exercise intervention was associated with positive changes in prevalence and intensity of musculoskeletal and psychosomatic complaints, better physiotherapy status (less muscle tightness, better neck mobility, and less tender points), increased shoulder strength and increased coordination in thigh muscles. However, the exercise group reported worse situations post-exercise concerning aspects of their physical and psychosocial work-environment (i.e., concerning ergonomy, influence, appreciation and communication with work manager), which might have been due to stress associated with the exercise situation.

ARE PERCEIVED MUSCLE TENSION, ELECTROMYOGRAPHIC HYPERACTIVITY AND PERSONALITY TRAITS CORRELATED IN THE FIBROMYALGIA SYNDROME?

The study was performed to investigate the relationship between perceived muscle tension and electromyographic hyperactivity and to what extent electromyographic (EMG) hyperactivity relates to personality traits in fibromyalgics. Thirty-six females with fibromyalgia performed isokinetic maximal forward flexions of the shoulder combined with surface EMG recordings of the trapezius and infraspinatus muscles. Signal amplitude ratio and peak torque were calculated in the initial and endurance test phases. Pain intensity, perceived general and local shoulder muscle tension, and personality traits using the Karolinska Scales of Personality were assessed pre-test. Neither perceived muscle tension nor muscular tension personality trait correlated with EMG muscle hyperactivity. Perceived general muscle tension correlated with aspects of anxiety proneness (including muscle tension) of the Karolinska Scales of Personality. Pain intensity interacted with many of the variables. We propose that when patients with fibromyalgia report muscle tension that they may be expressing something other than physiological muscle tension.

Worsening of neck and shoulder complaints in humans are correlated with frequency parameters of electromyogram recorded 1-year earlier

Abstract The aim was to investigate whether output and electromyogram (EMG) variables obtained from an isokinetic endurance test of the shoulder flexor muscles of 23 women with neck and shoulder problems in a car and truck industry correlated with improvement or worsening of complaints 1 year later. Each subject performed 100 maximal isokinetic shoulder forward flexions at 60° · s−1. Surface EMG of the trapezius, deltoid, biceps brachii and infraspinatus muscles and mechanical output (peak torque) were determined for each contraction. The EMG was used to determine mean frequency fmean and the ratio between the signal amplitudes of the EMG of the passive relaxation and active flexion parts of each contraction cycle (SAR). The subjects also rated the degree of fatigue they experienced throughout the test. The magnitude of the shift in fmean was correlated with whether improvement or worsening occurred for complaints in the neck and or shoulders; a significant relationship (r2 = 0.44; P = 0.001) existed between the total frequency shift of the four muscles and the variables measuring improvement in complaints. In the multivariate predictions other fmean variables and perception of fatigue were also of significance. The present study would indicate that a high degree of fmean shift correlates with improvement in neck and shoulder complaints 1 year later. One possible reason could be that fmean reflects the muscle morphology and/or a pathological situation for the type-1 muscle fibres.

Lack of gender differences in the ability to relax between repetitive maximum isokinetic shoulder forward flexions : A population-based study among northern Swedes

Abstract The aim of the present study was to analyse the effects of gender and age in a population-based sample of clinically healthy subjects on: (1) strength, endurance and perception of fatigue, (2) mean frequency (MNF) of the electromyogram (EMG), and (3) the ability to relax between active contractions (signal amplitude ratio; SAR) of the surface EMG of an isokinetic shoulder forward flexion test. With this aim we have analysed aspects of the validity of MNF as an indicator of fatigue, using peak torque as a criterion variable. The subjects were 27 men and 28 women (age range: 20–60 years), who were obtained by random sample from the official census lists (participation rate: 66%). The peak torque and surface EMG of two portions of the trapezius, deltoid and infraspinatus muscles were recorded throughout 100 repetitive maximal isokinetic shoulder forward flexions. No significant differences in the perception of fatigue and relative endurance levels of peak torque and work were found between males and females. Males were significantly stronger than females and, on average, females produced approximately 60% of the output of the males; 76% after normalisation for body mass. The men had significantly lower MNF endurance levels for three of the investigated muscles. When controlled for age and body mass, the men had a significantly higher MNF of the deltoid muscle than did the females. These differences were only found for the deltoid muscle. Significant correlations existed between the MNF of the four muscles and biomechanical output, indicating criterion validity for the MNF variable with respect to fatigue. There were no significant effects of gender or age on the ability to relax between repetitive contractions (SAR). The higher prevalence of musculoskeletal complaints of the neck-shoulder region in females cannot be explained by a higher intrinsic muscle tension. Age, gender, body mass index and biomechanical output can have significant effects upon MNF. These effects are important considerations in the interpretation of MNF, for instance in ergonomic situations.

Aspects of Criterion Validity and Sensitivity of the BAS-Health Scale in Chronic Pain Patients - A Pilot Study of Patients at a Multidisciplinary Pain Centre

A new body awareness scale (the BAS-H) has been recently developed. The aims of the present study were to investigate structure among the individual items, correlate the BAS-H with different aspects of pain, depression and incapacity benefit and to investigate whether it is sensitive as an outcome evaluation tool after rehabilitation. Subjects and methods: Patients with chronic pain participated. There were 54 patients with whiplash-associated disorders (the WAD group), 42 patients with long periods of incapacity benefit (the mixed pain group) and a sub-population (n=25) that took part in a rehabilitation program (the rehabilitation group). All patients were rated using the observation part of the BAS-H and answered questionnaires concerning aspects of depression, pain and incapacity benefit. Results: It was not possible to confirm that the three indices of the BAS-H were valid. Aspects of depression, pain and incapacity benefit correlated with the BAS-H only in the WAD group. The rehabilitation group sho...