Changed activation, oxygenation, and pain response of chronically painful muscles to repetitive work after training interventions: a randomized controlled trial.

The aim of this randomized controlled trial was to assess changes in myalgic trapezius activation, muscle oxygenation, and pain intensity during repetitive and stressful work tasks in response to 10 weeks of training. In total, 39 women with a clinical diagnosis of trapezius myalgia were randomly assigned to: (1) general fitness training performed as leg-bicycling (GFT); (2) specific strength training of the neck/shoulder muscles (SST) or (3) reference intervention without physical exercise. Electromyographic activity (EMG), tissue oxygenation (near infrared spectroscopy), and pain intensity were measured in trapezius during pegboard and stress tasks before and after the intervention period. During the pegboard task, GFT improved trapezius oxygenation from a relative decrease of -0.83 ± 1.48 µM to an increase of 0.05 ± 1.32 µM, and decreased pain development by 43%, but did not affect resting levels of pain. SST lowered the relative EMG amplitude by 36%, and decreased pain during resting and working conditions by 52 and 38%, respectively, without affecting trapezius oxygenation. In conclusion, GFT performed as leg-bicycling decreased pain development during repetitive work tasks, possibly due to improved oxygenation of the painful muscles. SST lowered the overall level of pain both during rest and work, possibly due to a lowered relative exposure as evidenced by a lowered relative EMG. The results demonstrate differential adaptive mechanisms of contrasting physical exercise interventions on chronic muscle pain at rest and during repetitive work tasks.

Effect of cycling on oxygenation of relaxed neck/shoulder muscles in women with and without chronic pain.

Work-related neck/shoulder muscle pain has been associated with increased anaerobic muscle metabolism. Thus, interventions to enhance oxygenation of painful muscles seem relevant. While cycling with relaxed shoulders has been shown to result in acute neck/shoulder muscle pain reduction, the effect on tissue oxygenation remains unknown. The aim of the present study was to investigate tissue oxygenation of the passive trapezius muscle during and after cycling in female workers with (MYA) and without (CON) trapezius myalgia. Eligible participants (n = 17 MYA, n = 8 CON) performed 20 min sub-maximal cycling in an upright position with relaxed shoulders. Near-infrared spectroscopy was used to measure trapezius muscle oxygenation during and 2 min after the cycling period. For both MYA and CON, oxygenation of the passive trapezius increased in a linear fashion over time, to values approximately 5 microM above baseline at the end of the cycling period, with no significant group difference (CON 5.2, MYA 4.9 microM). Two min after termination of exercise, oxygenation was increased further in both groups, but significantly more in CON (8.8 microM) than in MYA (7.0 microM) (P = 0.05). In conclusion, cycling increases oxygenation of resting neck/shoulder muscles in women with and without trapezius myalgia, indicating acute positive effects of either neural or humoral factors on vascular beds of distant relaxed muscles. Although this beneficial response was observed in both groups, the post-exercise response was lower in women with trapezius myalgia.

Effect of physical training on pain sensitivity and trapezius muscle morphology.

The objective of this study was to investigate morphological and physiological characteristics of painful muscles in women with (MYA, n= 42) and without (CON, n = 20) trapezius myalgia, and assess changes in response to a 10-week, randomized, controlled trial. MYA accomplished: (1) specific strength training (SST); (2) general fitness training (GFT); or (3) reference intervention (REF). Differences in muscle morphology could not be detected by ultrasound imaging. Significantly lower pressure pain threshold (PPT) and shoulder torque were observed for MYA, indicating pain-related lack of full activation. After 10 weeks, increased shoulder torque and PPT of the painful trapezius were observed in SST solely. The PPT of a pain-free reference muscle was increased in response to both SST and GFT, indicating a general effect of physical activity on pain perception. This study shows clinically relevant improvement in pain sensitivity and muscle strength capacity in response to SST.

Assessment of work-related muscle strain by using surface EMG during test contractions interposed between work periods of simulateted mushroom picking.

Surface electromyograms(EMG) during test contractions (TCs) were studied to assess the muscle strain in simulated mushroom picking. Additionally, the duration of the TC for the effective assessment was investigated. Nine female subjects performed standardized shoulder abduction and a stooped posture for one minute as TCs. Each experiment consisted of a 60-min rest, three work periods (W1-W3), a 30-min rest, and two work periods (W4 and W5) separated by a 30-min rest period. The duration of each work period was about 20 min. A total of 18 TCs was performed between the work periods and every 10 minutes in the rest periods. EMGs were recorded from the trapezius, infraspinatus, deltoid, and erector spinae muscles. The amplitude of EMG (AEMG) and mean power frequency (MPF) of EMG were calculated. Each TC was divided equally into three parts. Ratings of perceived exertion (RPE) in the neck, shoulder and low-back were reported during TCs. The work increased RPE of all the parts. AEMG and RPE were increased and MPF was decreased by W1, W2 and W3 in the neck and shoulder muscles. MPF of the erector spinae was increased by the work. The results were not affected by the duration of TCs and the parts during the TCs. AEMG and MPF fluctuated before W1 although the changes of RPE were small. Averaging several TCs was recommended to get stable results from TCs. EMG changes and appropriate TC conditions were discussed in relation to the adaptation in fatiguing contractions.

Stress reactions to cognitively demanding tasks and open-plan office noise.

OBJECTIVES: To investigate the effects of cognitively demanding work tasks and office noise on heart rate variability (HRV), cardiovascular responses and electromyography (EMG) activity in the trapezius muscles. METHODS: Ten female volunteers were exposed to simulated open-plan office noise for 35 min (Leq 65 dBA), while engaged in cognitively demanding tasks. Task performance, self-rated stress and energy, affective state, perceived exertion in the shoulders and in the head, EMG in the left and right trapezius muscle, blood pressure, heart period length, HRV, and salivary cortisol were measured. RESULTS: Cognitively demanding work tasks were associated with changes in HRV, systolic blood pressure and EMG that reflects increased sympathetic activity in the autonomic nervous system. No effect of noise was observed, except for a higher rating of perceived exertion in the head and, contrary to expectations, a 4% lower diastolic blood pressure in the noise conditions. CONCLUSIONS: Psychophysiological measures reflected the mental load imposed by cognitive work tasks. Short-term exposure to office noise resulted in increased ratings of perceived exertion in the head, but not in physiological stress reactions.

Ocular surface area and human eye blink frequency during VDU work: the effect of monitor position and task.

The purpose of this study was to investigate how the ocular surface area (OSA) and the eye blink frequency (BF) are affected by a high versus a low-monitor position during visual display unit (VDU) work with varying cognitive demands. In a balanced randomized (2 x 2) design ten healthy subjects (five males, five females) completed two different tasks on the VDU in a simulated office environment (23 degrees C and 30-35% relative humidity); an active task with demands on vision and hand-eye coordination, and a passive task. Two monitor positions were used: high (the monitors' upper edge at the same height as the subjects' eyes) and low (lowered by 25 degrees and perpendicular to gaze angle). Each task lasted 10 min. An OSA-proxy was measured from video recordings, and BF was sampled by electrooculography. The effect of lowering the gaze angle by 25 degrees decreased the OSA-proxy significantly (P < 0.01) during the active task, indicating that a low position of the monitor may be preferable even though the BF also decreased. Overall, the OSA-proxy was 6% higher during the active task compared to the passive while BF during the active task was 69% lower than during the passive task. The low BF during the active task was succeded by a burst with high BF after cessation of the active task, indicating a compensatory blinking process. This stresses that interchange of work tasks with different cognitive load is as important as the monitor position in the prevention of visual and musculoskeletal disorders.

The assessment of muscle strain with surface electromyograms during simulated mushroom picking.

Muscle strain was assessed with surface EMG during simulated mushroom picking. Nine female subjects performed five periods of work (W1-W5). The duration of each period was about 20 min. W1, W2 and W3 were separated by a short break of several minutes. W3, W4 and W5 were separated by a rest period of about 43 min. EMGs were recorded from the muscles of trapezius, infraspinatus, deltoid and erector spinae muscles. Amplitude of EMG (AEMG) and mean power frequency (MPF) of EMG were calculated every minute. Ratings of perceived exertion (RPE) were recorded for every 5 min. RPE increased during each work period and with the advance of W1-3. AEMG increased during some of the work periods in the trapezius and infraspinatus. AEMG decreased in a few of the work periods in the other muscles. MPF decreased during some of the work periods in the infraspinatus, deltoid and erector spinae. The increase of AEMG in the trapezius was interpreted as spare capacity for the work. The infraspinatus and deltoid were assessed to be more fatigued than the trapezius. The fatigue level of the erector spinae was low.

The effects of shoulder load and pinch force on electromyographic activity and blood flow in the forearm during a pinch task.

The object of the current study was to determine whether static contraction of proximal musculature has an effect on the blood flow more distally in the upper extremity. Static contractions of muscles in the neck shoulder region at three levels (relaxed, shoulders elevated and shoulders elevated loaded with 4.95 kg each) were combined with intermittent pinch forces at 0, 10 and 25% of the maximum voluntary contraction (MVC). Blood flow to the forearm was measured with Doppler ultrasound. Myoelectric activity of the forearm and neck-shoulder muscles was recorded to check for the workload levels. Across all levels of shoulder load, blood flow increased significantly with increasing pinch force (21% at 10% MVC and by 44% at 25% MVC). Blood flow was significantly affected by shoulder load, with the lowest blood flow at the highest shoulder load. Interactions of pinch force and shoulder load were not significant. The myoelectric activity of forearm muscles increased with increasing pinch force. The activation of the trapezius muscle decreased with increasing pinch force and increased with increasing shoulder load. The precise mechanisms accounting for the influence of shoulder load remains unclear. The results of this study indicate that shoulder load might influence blood flow to the forearm.

Quantitative ultrasound tissue characterization in shoulder and thigh muscles--a new approach.

BACKGROUND: The echogenicity patterns of ultrasound scans contain information of tissue composition in muscles. The aim was: (1) to develop a quantitative ultrasound image analysis to characterize tissue composition in terms of intensity and structure of the ultrasound images, and (2) to use the method for characterization of ultrasound images of the supraspinatus muscle, and the vastus lateralis muscle. METHODS: Computerized texture analyses employing first-order and higher-order grey-scale statistics were developed to objectively characterize ultrasound images of m. supraspinatus and m. vastus lateralis from 9 healthy participants. RESULTS: The mean grey-scale intensity was higher in the vastus lateralis muscle (p < 0.05) than in the supraspinatus muscle (average value of middle measuring site 51.4 compared to 35.0). Furthermore, the number of spatially connected and homogeneous regions (blobs) was higher in the vastus lateralis (p < 0.05) than in the supraspinatus (average for m. vastus lateralis: 0.092 mm(-2) and for m. supraspinatus: 0.016 mm(-2)). CONCLUSION: The higher intensity and the higher number of blobs in the vastus lateralis muscle indicates that the thigh muscle contained more non-contractile components than the supraspinatus muscle, and that the muscle was coarser. The image analyses supplemented each other and gave a more complete description of the tissue composition in the muscle than the mean grey-scale value alone.