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Biomedical subjects

B Gerdle

Publications and source records attributed to B Gerdle.

At least 55 records · Page 3Linked to original sources
PubMed1994

The mean frequency of the EMG of the knee extensors is torque dependent both in the unfatigued and the fatigued states.

The present study aimed to investigate the shift in the mean frequency (fmean) of the power density spectrum of the electromyogram (EMG) during endurance tests of the knee extensors at three different torque levels (70% MVC, 25% MVC and 10% MVC). Fourteen clinically healthy men performed the three endurance tests until exhaustion. Surface EMG(s) were obtained from the vastus medialis, the vastus lateralis and the rectus femoris muscles and fmean and signal amplitude (RMS) were computed. The subjects rated the perception of fatigue in the knee extensor muscles throughout the three tests using a 10-point graded scale. The endurance time increased with decreasing torque level. A significantly higher perception of fatigue was found at the low torque level (10% MVC) at the end of the endurance time. Individual time series analysis (using linear regression) was performed. It was found that linear models described well the behaviour of fmean throughout the endurance time at the three torque levels. When the endurance times were normalized significant differences in the rate of decrease in fmean were found for vastus lateralis and rectus femoris; the rate decreased with decreasing torque level. For these two muscles significant differences were also found in fmean in the unfatigued state; at 10% MVC significantly lower fmean was found. The present study demonstrated both that the unfatigued fmean and the rate of decrease in fmean (with normalized endurance time) were torque dependent. The latter finding, combined with our result that the subjective fatigue was highest at the lowest torque level, calls into question the use of fmean as a valid indicator of peripheral fatigue.

Adult↗
PubMed1994

Factors interacting with perceived work-related complaints in the musculoskeletal system among home care service personnel. An explorative multivariate study.

The interrelationships between reported complaints, certain sociodemographic data and ergonomic, physical and psychosocial aspects of the work-environment were investigated in a cross-sectional study of home care service personnel using a questionnaire. Ninety-seven out of 160 randomly selected women took part in pre-tests (presented here), post-tests and one year exercise program. Significant correlations existed between musculoskeletal complaints, other (somatic and psychosomatic) symptoms and anxiety/threat for differently, mainly work-related negative changes. The group of subjects could be divided into three subgroups. A "complaint group" was identified with a high prevalence of musculoskeletal and other somatic/psychosomatic symptoms. This group had the most negative ratings on the ergonomic and physical work-environment indices. A "young group" had the most negative perception of the psychosocial work-environment. The "healthy group" generally perceived the situation best. The present preliminary study could indicate that work-related interventions/rehabilitation programmes undertaken for the complaint group must be designed in another way and with other goals than those directed towards the other two identified groups.

Adult↗
PubMed1993

Fatigue in the shoulder muscles during static work at two different torque levels.

The present study aimed to investigate whether and when a shift in the mean power frequency (MPF) of the electromyogram (EMG) occurs at low torque levels during a maximum endurance test of three shoulder flexors. Twelve clinically healthy women performed two endurance tests of the shoulder flexors (at 50% MVC--the high torque level, and at approximately 18% MVC--the low torque level) until maximum exhaustion. Surface EMG were obtained and MPF and signal amplitude (RMS) were computed for the trapezius descendens, the anterior part of the deltoid and the infraspinatus. The subjects also rated the perception of fatigue in the shoulder muscles throughout the two tests using a 10-graded scale. A significantly higher degree of perceived fatigue was found at the low rather than at the high torque level. In contrast significantly lower MPF were found at the end of the endurance times in the three muscles at the high torque level when compared to the low torque level. At the low torque level MPF of the trapezius was constant throughout the test. In the deltoid the most prominent decrease occurred during the initial 30-40% of the endurance time at the low torque level. It is suggested that the MPF shift mainly reflects peripheral fatigue of the type-2 fibres. The results of the present study question the use of the MPF shift to monitor peripheral fatigue in the fibres active (mainly type-1) at low torque levels.

Adult↗
PubMed1992

Is the mean power frequency shift of the EMG a selective indicator of fatigue of the fast twitch motor units?

During repeated maximum isokinetic contractions parallel decreases in output and the mean power frequency (MPF) of the electromyogram (EMG) occur, followed by stable levels (the endurance level). This study aimed to investigate if hypoxia of the plantar flexors will result in a shift in MPF during the endurance level. Mechanical performance and simultaneous surface EMG activity of three plantar flexors (m. soleus, m. gastrocnemius medialis and m. gastrocnemius lateralis) were recorded during repeated isokinetic plantar flexions at 1.05 rad s-1 in 10 healthy women. The study consisted of two tests with 14 days in between: (1) a maximum test consisting of 125 maximum plantar flexions. After 100 contractions, using a tourniquet, a relative ischaemia (hypoxia) was induced. (2) a submaximum test performed at the level established between contractions 70-100 of the maximum test, consisting of 125 plantar flexions. During the maximum test mechanical performance output, the signal amplitude (RMS) of the EMG and the MPF decreased in parallel during the initial 50 contractions followed by stable levels during the subsequent 50 contractions. When hypoxia was induced decreases in mechanical performance and RMS appeared without significant decreases in MPF. The present study indicates that the MPF shift is mainly sensitive to biochemical changes in the type 2 fibres. Hypoxia mainly located to the type 1 fibres will not be detected using the MPF variable.

Adult↗
PubMed1992

Mechanical performance, level of continuous contraction and muscle pain symptoms in home care personnel.

The interrelationships between reported complaints, clinical status, mechanical performance and EMG pattern of the shoulder flexors and the knee extensors, respectively, during maximum dynamic contractions were investigated. A group of 97 randomly selected women employed in the home care service participated. Those who reported complaints had more clinical findings, such as reduced mobility, tender points and muscle tightness, than non-complainers. The level of muscle activity during the passive part of the contraction cycle was significantly higher in the shoulder flexors than in the knee extensors. Subjects without reported complaints who had been employed for more than ten years had a significantly lower activity level in the shoulder muscles than subjects without complaints who had been employed for a shorter time. We suggest that a high muscle tension level between contractions might precede muscle pain. A cluster analysis including sociodemographic, clinical and physiological variables revealed different subgroups, which points to the need to investigate the work situation in a multivariate way.

Adult↗
PubMed1991

Dependence of the mean power frequency of the electromyogram on muscle force and fibre type.

The aim of this study was to investigate whether the mean power frequency of the electromyogram of the knee extensors was force and/or muscle fibre-type dependent. Ten female subjects performed a gradually increasing static knee extension (5 seconds duration) using an isokinetic dynamometer. Electromyogram-signals were obtained from the vastus lateralis, vastus medialis and the rectus femoris muscles. The torque signal and the three electromyogram signals were recorded on a tape recorder. From the electromyogram recordings the mean power frequency and the signal amplitude were determined. Muscle biopsies were later obtained from the right vastus lateralis and stained for alkaline and acid mATPase for the determination of fibre-type proportion and areas. Both the mean power frequencies and the signal amplitudes of the three knee extensors were positively torque dependent. Furthermore it was found that the fibre type proportion and the regression coefficient of the torque (%)-mean power frequency relationship were positively correlated. Also a negative correlation existed between the type-1 (%) proportion and the intercept of the individual torque (%)-mean power frequency relationships. In contrast to proposed models of the electromyogram signal no correlation was found between the mean power frequency and the fibre area.

Action Potentials↗
PubMed1990

The behaviour of the mean power frequency of the surface electromyogram in biceps brachii with increasing force and during fatigue. With special regard to the electrode distance.

The present study aims to investigate: a) the relationship between force and mean power frequency of the EMG, and b) how the distance between surface electrodes influences the mean power frequency. The study consisted of three parts: 1) a gradually increasing contraction upto 100% MVC, 2) contractions performed at 5 different levels from 20% upto 100% MVC with rest in between, and 3) an endurance test at 30% MVC. Nine healthy women participated. The elbow was flexed 90 degrees and EMG signals were obtained from the biceps brachii. The surface electrodes were placed so that electrode distances of 10 mm, 20 mm and 30 mm were obtained. The mean power frequency increased upto 60% MVC. Above 60% MVC no change in mean power frequency occurred. No differences in the mean power frequency with respect to the electrode distances existed at each force level. No significant differences were found at each contraction level between the gradually increasing contraction and the stepwise increasing contractions. The mean power frequency decreased linearly during the endurance test without any differences with respect to the electrode distances. It is concluded that the different electrode distances do not affect the mean power frequency-force relationship or the decrease in mean power frequency during fatigue. It is proposed that the increase in mean power frequency, on group level, can be used as an indicator of motor unit recruitment. However, this proposal was found to be complicated when individual analyses were made.

Adult↗
PubMed1989

Muscular fatigue during repeated isokinetic shoulder forward flexions in young females.

Peak torque, work, mean power and electromyographic (EMG) activity were recorded for each of 150 repeated isokinetic maximal shoulder flexions (45 degrees-90 degrees) in 23 healthy females. From the EMG signals of trapezius, deltoid, infraspinatus and biceps brachii the mean power frequency and the signal amplitude were determined in real time. The mechanical output showed a steep decrease during the first 40 contractions, followed by a plateau maintained until the end. In all muscles, except the biceps brachii, significant decreases in mean power frequency occurred during the first 40 contractions, showing a tendency to stabilize around the same absolute frequency value. Signal amplitude increased in the trapezius, the deltoid and the infraspinatus, but was constant in the biceps brachii. For some individuals rather high EMG activity was recorded in the muscles during the time the arm was supposed to be passively extended to the starting position, and this was found to be associated with lower strength and endurance levels. Longitudinal analyses showed that the mean power frequencies correlated better than the signal amplitudes with the three mechanical variables. The results suggest that the initial steep decrease in mechanical performance and mean power frequency is caused by fatiguing of type 2 motor units.

Adult↗
PubMed1989

The relationship between contraction and relaxation during fatiguing isokinetic shoulder flexions. An electromyographic study.

Knowledge of the strength, endurance and coordination of the shoulder muscles during dynamic contractions in healthy women would contribute to the understanding of symptoms in that part of the body in patients with myalgia. Twenty clinically healthy women performed single maximal forward shoulder flexions at four different angular velocities (0.57-3.14 rad.s-1). The same subjects also took part in two endurance tests (at angular velocities of 0.57 and 2.09 rad.s-1, respectively) consisting of 150 repeated maximal shoulder flexions. Electromyographic activity (EMG) was registered from four shoulder flexors using surface electrodes. Work was used as the mechanical variable. During the endurance tests subjects rated their perception of fatigue in the shoulder muscles. Work and the amplitude of the EMG signals decreaesd with angular velocity. The mean power frequency of the EMG was constant in the span of angular velocities investigated. During the endurance tests, work and the mean power frequency decreased during the initial 40-60 contractions followed by stable levels. The relative work level was higher at 2.09 than at 0.57 rad.s-1. Greater relative increases of the signal amplitudes of EMG occurred at 2.09 than at 0.57 rad.s-1. The EMG activity between the flexions (during the supposed passive extension) was higher at 2.09 than at 0.57 rad.s-1. Such a high activity was associated with a low mechanical performance at 2.09 rad.s-1. It is suggested that the initial sharp decreases in work and in mean power frequency reflect the fatiguing of the fast twitch motor units. Dynamic work consisting of continuous activity could predispose to muscle complaints.

Adult↗
PubMed1988

Changes in the surface electromyogram during increasing isometric shoulder forward flexions.

When using electromyographic techniques in the evaluation of muscular load it is necessary to determine the mathematical relationship between the torque and the amplitude of the electromyographic signal. Isometric gradually increasing contractions up to 100% MVC can then be used. Often more than linear increases for the amplitude (RMS)--force regression have been reported. The present study was designed to test whether changes in power spectral density function take place during a gradually increasing isometric contraction (duration 10 s). Twenty-two clinically healthy females performed an increasing isometric shoulder forward flexion for 10 s using an isokinetic dynamometer. Electromyographic activity was measured in trapezius, deltoid, infraspinatus and biceps brachii using surface electrodes. Mean torque values were determined together with mean power frequency (MPF) and root mean square values (RMS) from the EMG signals for each 256 ms period. The RMS-torque regressions showed higher regression coefficients during the 6th to 9th sec than during the first 5 s. No significant correlation existed between MPF for the four muscles and the torque. A gradual decrease in MPF was generally found from the 6th s. It is concluded that this decrease in power spectral density function might have contributed to the significantly higher regression coefficient for the RMS torque regression at the high output part of the gradually increasing isometric contraction.

Adult↗
PubMed1988

Surface EMG recordings during maximum static shoulder forward flexion in different positions.

This study investigated how position in the range of motion influences the power spectral density function during static shoulder forward flexion. 23 healthy females (20-30 years) volunteered as subjects. They performed maximum static shoulder forward flexions in three positions: 45, 65 and 90 degrees of shoulder flexion. An isokinetic dynamometer was used and the subjects were seated in a specially constructed chair to enable adequate fixation. The elbow was extended and the hand pronated. Electromyographic (EMG) signals (using surface electrodes) were obtained from the descending part of the right trapezius, the anterior portion of the right deltoid, the right infraspinatus and the common belly of the right biceps brachii. The four EMG-signals and the torque and shoulder angle were analyzed by computer. For each 256 ms, mean power frequency, root mean square value and mean torque were calculated. At each of the three positions four 256 ms periods were analyzed and the data are presented as their means. In the trapezius and the biceps brachii the mean power frequency did not change between the three positions. Deltoid and infraspinatus had significantly higher mean power frequencies at 90 degrees than at 45 degrees of flexion. Different factors behind the change in mean power frequency are discussed. The need to standardize the range of motion when studying dynamic fatiguing contractions is emphasised.

Adult↗
PubMed1988

Relationship between work and electromyographic activity during repeated leg muscle contractions in orienteers.

Contraction work (CW) was recorded for each of 200 repetitive isokinetic plantar flexions (1.05 rad.s-1) and knee extensions (1.57 rad.s-1) in 14 elite male orienteers. Simultaneous recordings of integrated electromyograms (iEMG) were obtained from the 3 parts of triceps surae and from 3 superficial portions of quadriceps femoris. CW in both muscle groups decreased significantly during the first 30 contractions (the fatigue phase), followed by a steady state level. The relative steady state level was higher for the plantar flexors (70 +/- 17%) than for the knee extensors (56 +/- 12%). For quadriceps a significant increase in iEMG occurred during the first 10 contractions followed by a decrease, whereas the iEMG of the plantar flexors showed a gradual decrease to the steady state level, which was similar for the two muscle groups (71-72%). The chosen expression of output/input balance (CW/iEMG) was constant throughout the plantarflexion test but decreased during the initial 20 knee extensions down to 82%. Thus, the fatigue phase of the knee extensions appeared to be divided into two; the first part had decreases in both CW and CW/iEMG and the second part with a decrease in CW alone. In contrast the plantar flexors only showed the characteristics of the second part.

Adult↗
PubMed1988

Mechanical output and iEMG of single and repeated isokinetic plantar flexions: a study of untrained and endurance-trained women.

Isokinetic plantar flexion peak torque (PT), contractional work (CW), and integrated electromyographic activity (iEMG) were analyzed in a group of untrained females and a group of female elite orienteers. Similar levels of PT, CW, and iEMG were observed in both groups during single maximum maneuvers (30-180 degrees s1). During repetitive (200) maximum plantar flexions, the untrained females showed a steeper and more pronounced decline in CW during the first 50 contractions than the orienteers. After this fatigue phase, all subjects could maintain a steady-state level of CW throughout the test. This level of CW was significantly (20%) higher in the orienteers than in the untrained females. The iEMGs of the gastrocnemii and soleus muscles decreased to significantly (10%) lower levels in the untrained women than in the orienteers. For both groups, the soleus muscle showed a significantly higher steady-state level of iEMG (10%) than mm. gastrocnemii. In the untrained group, CW/iEMG of m. triceps surae decreased to a plateau level significantly lower than in the orienteerers who could virtually maintain the initial CW/iEMG throughout the test. The differences observed could be explained by adaptations to performed endurance training in the orienteers.

Adult↗
PubMed1988

Do the fibre-type proportion and the angular velocity influence the mean power frequency of the electromyogram?

The dependence of the mean-power frequency and the signal amplitude of the electromyogram (EMG) on the angular velocity and the fiber-type proportion were investigated in nine female volunteers. The subjects were required to perform maximum knee extensions using an isokinetic dynamometer at different angular velocities; 0.57, 1.05, 1.57, 2.09 and 3.14 rad s-1. Electromyographic signals were obtained from the vastus lateralis, vastus medialis and the rectus femoris muscles. The angle and the torque signals were recorded simultaneously with the three EMG signals on a tape-recorder. From the EMG recordings the mean power frequency (MPF) and the signal amplitude were determined. Muscle biopsies were later obtained from the right vastus lateralis and stained for alkaline and acid mATPase for the determination of fibre-type proportions and areas. Neither the signal amplitude nor the MPF of the EMG of the three muscles were dependent on the angular velocity. The MPF of the vastus lateralis correlated significantly (r = -0.93) with the type 1 fibre proportion at 1.57 rad s-1. However, there was no significant correlation between the areas of the fibre types, alone or together, and the MPF. In conclusion the fibre-type proportion was the major factor behind the MPF irrespective of angular velocity.

Adenosine Triphosphatases↗
PubMed1988

Rank order of peak amplitude of EMG between the three muscles of triceps surae during maximum isokinetic contractions.

Peak torque (PT) of maximum isokinetic plantar flexions was measured at 4 angular velocities (30, 60, 120 and 180 degrees/s) in 88 subjects. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the three heads of m. triceps surae. Subjects were clinically healthy subjects randomly chosen in age-groups 40-44, 50-54 and 60-64 years. The delays (in degrees) in range of motion (from maximum dorsiflexed position) of PT and of peak value of the low-pass filtered EMG-amplitudes (pEMG) were determined and ranked. pEMG of gastrocnemius medialis was reached before m. gastrocnemius lateralis which reached pEMG before m. soleus. At 30 degrees/s PT coincided with the pEMG of m. soleus, while at 120 and 180 degrees/s PT coincided with pEMGs of mm. gastrocnemii. The fixed rank order of pEMGs in the three muscles might be a reflexion of differences in the motor unit populations in the mm. gastrocnemii and m. soleus. The findings indicate that the relative roles of the three muscles, when torque-production is concerned, is dependent on angular velocity.

Adult↗
PubMed1987

Repeated isokinetic plantar flexions at different angular velocities.

Peak torque (PT), contraction work (CW) and mean power (CP) were measured for each of 200 repetitive isokinetic (maximum effort) plantar flexions. Simultaneous recording of integrated electromyograms (iEMG) were obtained from the three parts of the triceps surae muscle. Four tests at different angular velocities (30, 60, 120 and 180 degrees s-1 (degrees X s-1] were performed with at least 2 weeks between each test. The subjects were eight clinically healthy females (24-36 years). At all four angular velocities CW, CP and PT decreased steeply during the first approximately 70 contractions, followed by a steady-state level with no further significant decreases. The relative decreases of PT and CP were significantly smaller than for CW at all velocities. The relative CW decline increased with angular velocity; the relative PT and CP decreases were not velocity dependent. Also iEMG activity decreased in two phases during the 200 contractions and were on a significantly lower relative level at 180 degrees X s-1. However the reduction of range of motion was significantly greater at 180 degrees X s-1 and when the iEMG activity was compensated for this decrease the relative decreases in electromyographic activity were similar at the four angular velocities. The results indicated that CW was more sensitive to fatigue than PT and CP and that CW fatigue was dependent on angular velocity.

Adult↗