Steffen Vangsgaard

Computer work and self-reported variables on anthropometrics, computer usage, work ability, productivity, pain, and physical activity

BackgroundComputer users often report musculoskeletal complaints and pain in the upper extremities and the neck-shoulder region. However, recent epidemiological studies do not report a relationship between the extent of computer use and work-related musculoskeletal disorders (WMSD).The aim of this study was to conduct an explorative analysis on short and long-term pain complaints and work-related variables in a cohort of Danish computer users.MethodsA structured web-based questionnaire including questions related to musculoskeletal pain, anthropometrics, work-related variables, work ability, productivity, health-related parameters, lifestyle variables as well as physical activity during leisure time was designed. Six hundred and ninety office workers completed the questionnaire responding to an announcement posted in a union magazine. The questionnaire outcomes, i.e., pain intensity, duration and locations as well as anthropometrics, work-related variables, work ability, productivity, and level of physical activity, were stratified by gender and correlations were obtained.ResultsWomen reported higher pain intensity, longer pain duration as well as more locations with pain than men (P < 0.05). In parallel, women scored poorer work ability and ability to fulfil the requirements on productivity than men (P < 0.05). Strong positive correlations were found between pain intensity and pain duration for the forearm, elbow, neck and shoulder (P < 0.001). Moderate negative correlations were seen between pain intensity and work ability/productivity (P < 0.001).ConclusionsThe present results provide new key information on pain characteristics in office workers. The differences in pain characteristics, i.e., higher intensity, longer duration and more pain locations as well as poorer work ability reported by women workers relate to their higher risk of contracting WMSD. Overall, this investigation confirmed the complex interplay between anthropometrics, work ability, productivity, and pain perception among computer users.

Changes in H reflex and neuromechanical properties of the trapezius muscle after 5 weeks of eccentric training: a randomized controlled trial

Trapezius muscle Hoffman (H) reflexes were obtained to investigate the neural adaptations induced by a 5-wk strength training regimen, based solely on eccentric contractions of the shoulder muscles. Twenty-nine healthy subjects were randomized into an eccentric training group (n = 15) and a reference group (n = 14). The eccentric training program consisted of nine training sessions of eccentric exercise performed over a 5-wk period. H-reflex recruitment curves, the maximal M wave (Mmax), maximal voluntary contraction (MVC) force, rate of force development (RFD), and electromyographic (EMG) voluntary activity were recorded before and after training. H reflexes were recorded from the middle part of the trapezius muscle by electrical stimulation of the C3/4 cervical nerves; Mmax was measured by electrical stimulation of the accessory nerve. Eccentric strength training resulted in significant increases in the maximal trapezius muscle H reflex (Hmax) (21.4% [5.5-37.3]; P = 0.01), MVC force (26.4% [15.0-37.7]; P < 0.01), and RFD (24.6% [3.2-46.0]; P = 0.025), while no significant changes were observed in the reference group. Mmax remained unchanged in both groups. A significant positive correlation was found between the change in MVC force and the change in EMG voluntary activity in the training group (r = 0.57; P = 0.03). These results indicate that the net excitability of the trapezius muscle H-reflex pathway increased after 5 wk of eccentric training. This is the first study to investigate and document changes in the trapezius muscle H reflex following eccentric strength training.

Mechanistic experimental pain assessment in computer users with and without chronic musculoskeletal pain

BackgroundMusculoskeletal pain from the upper extremity and shoulder region is commonly reported by computer users. However, the functional status of central pain mechanisms, i.e., central sensitization and conditioned pain modulation (CPM), has not been investigated in this population. The aim was to evaluate sensitization and CPM in computer users with and without chronic musculoskeletal pain.MethodsPressure pain threshold (PPT) mapping in the neck-shoulder (15 points) and the elbow (12 points) was assessed together with PPT measurement at mid-point in the tibialis anterior (TA) muscle among 47 computer users with chronic pain in the upper extremity and/or neck-shoulder pain (pain group) and 17 pain-free computer users (control group). Induced pain intensities and profiles over time were recorded using a 0-10 cm electronic visual analogue scale (VAS) in response to different levels of pressure stimuli on the forearm with a new technique of dynamic pressure algometry. The efficiency of CPM was assessed using cuff-induced pain as conditioning pain stimulus and PPT at TA as test stimulus.ResultsThe demographics, job seniority and number of working hours/week using a computer were similar between groups. The PPTs measured at all 15 points in the neck-shoulder region were not significantly different between groups. There were no significant differences between groups neither in PPTs nor pain intensity induced by dynamic pressure algometry. No significant difference in PPT was observed in TA between groups. During CPM, a significant increase in PPT at TA was observed in both groups (P < 0.05) without significant differences between groups. For the chronic pain group, higher clinical pain intensity, lower PPT values from the neck-shoulder and higher pain intensity evoked by the roller were all correlated with less efficient descending pain modulation (P < 0.05).ConclusionsThis suggests that the excitability of the central pain system is normal in a large group of computer users with low pain intensity chronic upper extremity and/or neck-shoulder pain and that increased excitability of the pain system cannot explain the reported pain. However, computer users with higher pain intensity and lower PPTs were found to have decreased efficiency in descending pain modulation.

Crossed responses found in human trapezius muscles are not H-reflexes.

Introduction: We sought to confirm the presence of crossed short‐latency reflexes in trapezius. Methods: Mmax and Hmax were measured in the ipsilateral trapezius in 10 subjects by percutaneous electrical stimulation of the accessory nerve and the cervical nerves of C3/4 respectively. Repeated stimulation of the C3/4 cervical nerves was performed during 3 different tasks (relaxation, contraction of ipsilateral side, contraction of contralateral side). Results: Ipsilaterally, responses increased significantly with an increase in the prestimulus electromyogram (EMG) and decreased significantly with a decrease in prestimulus EMG. Contralateral potentials increased significantly with contraction of the trapezius ipsilateral to the stimulus compared with contraction of the muscle in which they were recorded and decreased significantly with increasing distance from the ipsilateral side. Conclusions: We found ipsilateral and contralateral responses consistent with previous findings. However, we conclude that the contralateral response in trapezius is not a crossed reflex. Muscle Nerve 49:362–369, 2014

Between-day reliability of the trapezius muscle H-reflex and M-wave.

Introduction: The aim of this study was to investigate the between‐day reliability of the trapezius muscle H‐reflex and M‐wave. Methods: Sixteen healthy subjects were studied on 2 consecutive days. Trapezius muscle H‐reflexes were evoked by electrical stimulation of the C3/4 cervical nerves; M‐waves were evoked by electrical stimulation of the accessory nerve. Relative reliability was estimated by intraclass correlation coefficients (ICC2,1). Absolute reliability was estimated by computing the standard error of measurement (SEM) and the smallest real difference (SRD). Bland–Altman plots were constructed to detect any systematic bias. Results: Variables showed substantial to excellent relative reliability (ICC = 0.70–0.99). The relative SEM ranged from 1.4% to 34.8%; relative SRD ranged from 3.8% to 96.5%. No systematic bias was present in the data. Conclusions: The amplitude and latency of the trapezius muscle H‐reflex and M‐wave in healthy young subjects can be measured reliably across days. Muscle Nerve 52: 1066–1071, 2015

A new method to diagnose neuromuscular disorders in the neck-shoulder region

The H-reflex is often used in the clinic as a tool to test for cervical radiculopathy or other neurologic disorders. Additionally, it is often used experimentally to investigate neural changes at a segmental level following an intervention (e.g. strength training) (1). Methods for recording H-reflexes in the soleus and tibialis anterior muscles have been thoroughly tested. However, only few studies have assessed H-reflexes of the upper extremity (2).

Ergonomics in sports and at work

This paper addresses issues related to ergonomics in sports and at work. Ergonomics and sports science disciplines are interrelated. Workers and athletes operate in demanding environments requiring a high level of performance. Thus, a branch of ergonomics focuses on quantifying motor strategies in order to optimize human performance and prevent injuries. These goals can be pursued by (i) assessing human characteristics and capabilities in relation to certain motor tasks, (ii) achieving optimal efficiency and improving the overall level of performance, (iii) reducing discomfort level, and (iv) ensuring safety. This paper reviews recent studies and presents novel methods used to assess human performance.