Gisela Sjøgaard

Muscle blood flow during isometric activity and its relation to muscle fatigue

SummaryThe effect of isometric exercise on blood flow, blood pressure, intramuscular pressure as well as lactate and potassium efflux from exercising muscle was examined. The contractions performed were continuous or intermittent (5 s on, 5 s off) and varied between 5% and 50% maximal voluntary contraction (MVC). A knee-extensor and a hand-grip protocol were used. Evidence is presented that blood flow through the muscle is sufficient during low-level sustained contractions (<10% MVC). Despite this muscle fatigue occurs during prolonged contractions. One mechanism for this fatigue may be the disturbance of the potassium homeostasis. Such changes may also play a role in the development of fatigue during intermittent isometric contractions and even more so in the recovery from such exercise. In addition the role of impaired transport of substances within the muscle, due to longlasting daily oedema formation, is discussed in relation to fatigue in highly repetitive, monotonous jobs.

The role of muscle activity and mental load in the development of pain and degenerative processes at the muscle cell level during computer work

The role of muscle activity and mental load in the development of pain and degenerative processes on the muscle cellular level during computer work : European Journal of Applied Physiology

Effect of two contrasting types of physical exercise on chronic neck muscle pain

OBJECTIVE The prevalence of neck muscle pain has steadily increased and especially pain from the descending part of the trapezius muscle has been associated with monotonous work tasks such as computer work. Physical exercise is generally recommended as treatment, but it is unclear which type of training is most effective. Our objective was to determine the effectiveness of specific strength training of the painful muscle versus general fitness training without direct involvement of the painful muscle (leg bicycling) on work-related neck muscle pain. METHODS We conducted a randomized controlled trial and recruited subjects from 7 workplaces characterized by monotonous jobs (e.g., computer-intensive work). Forty-eight employed women with chronic neck muscle pain (defined as a clinical diagnosis of trapezius myalgia) were randomly assigned to 10 weeks of specific strength training locally for the affected muscle, general fitness training performed as leg bicycling with relaxed shoulders, or a reference intervention without physical activity. The main outcome measure was an acute and prolonged change in intensity of neck muscle pain (100-mm visual analog scale [VAS]). RESULTS A decrease of 35 mm (approximately 79%; P<0.001) in the worst VAS pain score over a 10-week period was seen with specific strength training, whereas an acute and transient decrease in pain (5 mm; P<0.05) was found with general fitness training. CONCLUSION Specific strength training had high clinical relevance and led to marked prolonged relief in neck muscle pain. General fitness training showed only a small yet statistically significant acute pain reduction.

The effect of short‐term strength training on human skeletal muscle: the importance of physiologically elevated hormone levels

The effect of strength training and endogenously elevated hormone levels (plasma testosterone, growth hormone (GH) and cortisol) was studied in 16 young untrained males, divided into an arm only training group, A, and a leg plus arm training group, LA, in order to increase circulating levels of anabolic hormones. Both groups performed the same one‐sided arm training for 9 weeks, twice a week. Group A trained only one arm (AT), the contralateral arm serving as control (AC), whereas group LA additionally trained their legs following the training of the one arm (LAT), with the contralateral arm serving as control (LAC). In spite of the attempt to match the two groups, the initial isometric arm strength was 20–25% lower for group LA compared to group A (significant for the arm to be trained). Isometric strength increased significantly in LAT and LAC by 37% and 10%, respectively, while the 9% and 2% increases in AT and AC, respectively, remained insignificant. Isokinetic strength increased at one out of three velocities tested for the trained arm relative to the untrained arm in both group A and group LA (P<0.05). Functional strength increased significantly by 20% in LAT, 18% in LAC, 19% in AT, and 17% in AC. Hormonal responses were monitored during the first and last training sessions. Resting hormone levels remained unchanged for both groups. However, during the first training session plasma testosterone as well as plasma cortisol increased significantly in group LA but not in group A. Plasma GH rose in all exercise tests, except during the last test in group LA, but was significantly higher in group LA than in group A in the first training session. In conclusion, a larger relative increase in isometric strength was found in the group having the highest hormonal response. However, due to the initial difference in isometric strength caution must be taken with the interpretation of this finding, which may only indicate a possible link between anabolic hormones and muscle strength with training.

The health paradox of occupational and leisure-time physical activity

Background Occupational and leisure-time physical activity are considered to provide similar health benefits. The authors tested this hypothesis. Methods A representative sample of Danish employees (n=7144, 52% females) reported levels of occupational and leisure-time physical activity in 2005. Long-term sickness absence (LTSA) spells of ≥3 consecutive weeks were retrieved from a social-transfer payment register from 2005 to 2007. Results 341 men and 620 females experienced a spell of LTSA during the period. Cox analyses adjusted for age, gender, smoking, alcohol, body mass index, chronic disease, social support from immediate superior, emotional demands, social class and occupational or leisure-time physical activity showed a decreased risk for LTSA among workers with moderate (HR 0.85, CI 0.72 to 1.01) and high (HR 0.77, CI 0.62 to 0.95) leisure-time physical activity in reference to those with low leisure-time physical activity. In contrast, an increased risk for LTSA was shown among workers with moderate (HR 1.59, CI 1.35 to 1.88) and high (HR 1.84, CI 1.55 to 2.18) occupational physical activity referencing those with low occupational physical activity. Conclusion The hypothesis was rejected. In a dose–response manner, occupational physical activity increased the risk for LTSA, while leisure-time physical activity decreased the risk for LTSA. The findings indicate opposing effects of occupational and leisure-time physical activity on global health.

A model predicting individual shoulder muscle forces based on relationship between electromyographic and 3D external forces in static position

To study the potentiality for developing an EMG-based model for the human shoulder, mapping of relations between static hand forces and electromyographic (EMG) activity of 13 shoulder muscles, were performed. The procedure was to perform by the hands slowly varying isometric forces up to 20% maximum voluntary force in the three-dimensional space. By combining these data with literature values on muscle physiological cross-sectional area and moment arm data, an EMG-based model was developed for estimating muscle forces in the glenohumeral joint. The model was validated for one standardized position by comparing joint moment, calculated from EMG by using the model, with moments from the external force. The highest correlation between these moments was found assuming a linear EMG/force calibration at low force level (< 20% MVC), giving correlations from 0.65 to 0.95 for the abduction/adduction moment and from 0.70 to 0.93 for the flexion/extension moment, for the six subjects. Moments calculated from EMG were for most subjects somewhat lower than the moments from the external force; the mean residual error ranged from 1.6 to 9.9 Nm. Taking this into account, the results can be used for assessment of muscle forces based on recordings of external forces at the hands during submaximal static work tasks without substantially elevated arms.

Effect of physical exercise interventions on musculoskeletal pain in all body regions among office workers: A one-year randomized controlled trial

This study investigated effects of physical exercise on musculoskeletal pain symptoms in all regions of the body, as well as on other musculoskeletal pain in association with neck pain. A single blind randomized controlled trial testing a one-year exercise intervention was performed among 549 office workers; specific neck/shoulder resistance training, all-round physical exercise, or a reference intervention. Pain symptoms were determined by questionnaire screening of twelve selected body regions. Case individuals were identified for each body region as those reporting pain intensities at baseline of 3 or more (scale of 0-9) during the last three months. For neck cases specifically, the additional number of pain regions was counted. Intensity of pain decreased significantly more in the neck, low back, right elbow and right hand in cases of the two exercise groups compared with the reference group (P<0.0001-0.05). The additional number of pain regions in neck cases decreased in the two exercise groups only (P<0.01-0.05). In individuals with no or minor pain at baseline, development of pain was minor in all three groups. In conclusion, both specific resistance training and all-round physical exercise for office workers caused better effects than a reference intervention in relieving musculoskeletal pain symptoms in exposed regions of the upper body.

Worksite interventions for preventing physical deterioration among employees in job-groups with high physical work demands: Background, design and conceptual model of FINALE

BackgroundA mismatch between individual physical capacities and physical work demands enhance the risk for musculoskeletal disorders, poor work ability and sickness absence, termed physical deterioration. However, effective intervention strategies for preventing physical deterioration in job groups with high physical demands remains to be established. This paper describes the background, design and conceptual model of the FINALE programme, a framework for health promoting interventions at 4 Danish job groups (i.e. cleaners, health-care workers, construction workers and industrial workers) characterized by high physical work demands, musculoskeletal disorders, poor work ability and sickness absence.Methods/DesignA novel approach of the FINALE programme is that the interventions, i.e. 3 randomized controlled trials (RCT) and 1 exploratory case-control study are tailored to the physical work demands, physical capacities and health profile of workers in each job-group. The RCT among cleaners, characterized by repetitive work tasks and musculoskeletal disorders, aims at making the cleaners less susceptible to musculoskeletal disorders by physical coordination training or cognitive behavioral theory based training (CBTr). Because health-care workers are reported to have high prevalence of overweight and heavy lifts, the aim of the RCT is long-term weight-loss by combined physical exercise training, CBTr and diet. Construction work, characterized by heavy lifting, pushing and pulling, the RCT aims at improving physical capacity and promoting musculoskeletal and cardiovascular health. At the industrial work-place characterized by repetitive work tasks, the intervention aims at reducing physical exertion and musculoskeletal disorders by combined physical exercise training, CBTr and participatory ergonomics. The overall aim of the FINALE programme is to improve the safety margin between individual resources (i.e. physical capacities, and cognitive and behavioral skills) and physical work demands, and thereby reduce the physical deterioration in a long term perspective by interventions tailored for each respective job-group.DiscussionThe FINALE programme has the potential to provide evidence-based knowledge of significant importance for public health policy and health promotion strategies for employees at high risk for physical deterioration.Trial registrationsISRCTN96241850, NCT01015716 and NCT01007669

A Randomized Controlled Intervention Trial to Relieve and Prevent Neck/Shoulder Pain.

PURPOSE The objective of this study is to investigate the effect of three different workplace interventions on long-term compliance, muscle strength gains, and neck/shoulder pain in office workers. METHODS A 1-yr randomized controlled intervention trial was done with three groups: specific resistance training (SRT, n = 180), all-round physical exercise (APE, n = 187), and reference intervention (REF, n = 182) with general health counseling. Physical tests were performed and questionnaires answered at pre-, mid-, and postintervention. The main outcome measures were compliance, changes in maximal muscle strength, and changes in intensity of neck/shoulder pain (scale 0-9) in those with and without pain at baseline. RESULTS Regular participation was achieved by 54%, 31%, and 16% of those of the participants who answered the questionnaire in SRT (78%), APE (81%), and REF (80%), respectively, during the first half of the intervention period, and decreased to 35%, 28% and 9%, respectively, during the second half. Shoulder elevation strength increased 9-11% in SRT and APE (P < 0.0001). Participants with neck pain at baseline decreased the intensity of neck pain through SRT, from 5.0 +/- 0.2 to 3.4 +/- 0.2 (P < 0.0001), and through APE, from 5.0 +/- 0.2 to 3.6 +/- 0.2 (P < 0.001), whereas REF caused no change. For participants without shoulder pain at baseline, there was a significantly greater increase in pain over the 1-yr period in REF compared with SRT and APE (P < 0.01). CONCLUSION Compliance was highest in SRT but generally decreased over time. SRT and APE caused increased shoulder elevation strength, were more effective than REF to decrease neck pain among those with symptoms at baseline, and prevent development of shoulder pain in those without symptoms at baseline.

Effect of speed and precision demands on human shoulder muscle electromyography during a repetitive task

Abstract Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied during a hand movement task where five points were marked repeatedly with a pencil. Six female subjects performed with three precision demands and at four speeds. Three of the speeds were predefined, while the last speed was performed as fast as possible. The EMG were recorded from 13 shoulder muscles or parts of muscles. Elbow velocity, acceleration and rectified EMG were calculated for each task. The mean elbow velocity and acceleration increased with speed and precision demands. There was an increase in EMG as the speed demand increased for all three precision demands (P < 0.001), and as the precision demand increased for the two highest predefined speed demands (P < 0.05). The combination of a high speed and a high precision demand resulted in the highest EMG. Different EMG levels were attained for the 13 muscles and the supraspinatus muscle always showed the highest normalized EMG. However, analysis of variance showed the same relative increase for all muscles with speed and precision demands. The EMG changes in response to precision demand can only be explained in part by the differences in movement velocity and acceleration, and other factors such as increased co-contraction must also be taken into account.