Objective. To quantify the relative contribution of work-related physical and psychosocial factors, individual factors, and health-related factors to the development of more severe musculoskeletal pain in the neck and upper limbs and the back and lower limbs.Methods. In this cohort study of 5,604 workers from industrial and service companies, we collected information on work-related physical and psychosocial exposures and on individual and health-related factors. Questionnaires were completed at baseline by 4,006 participants (71.5%) and after 24 months by 3,276 (82%). At followup, participants with no or minor pain were included in Cox regression analyses to determine which factors predicted more severe regional pain.Results. Of the 4,006 baseline respondents, only 7.7% were free of regional pain. A total of 1,513 participants were free of severe pain at baseline and completed the 24-month followup. Highly repetitive work predicted arm pain, heavy lifting and prolonged standing predicted low back pain, and heavy pushing or pulling predicted lower limb pain. Low job satisfaction predicted neck/shoulder pain and lower limb pain, whereas other psychosocial work place factors were only of marginal importance. High levels of fear avoidance were associated with arm pain and lower limb pain. A high body mass index was highly associated with lower limb pain.Conclusion. Very few workers are totally free of pain in musculoskeletal regions, and we question the concept of incidence of musculoskeletal pain. The transition from no or minor pain to more severe pain was influenced by physical and psychosocial work place factors together with individual and health-related factors.Regional musculoskeletal pain is common in working populations and in the general population (1-4). Within the last 30 years, much effort has been put into research to identify risk factors for primary prevention, first by focusing on physical hazards in the work place (e.g., heavy lifting, awkward postures, repetitive movements) and second by also introducing psychosocial work place factors (e.g., job demands, job control, social support, and job satisfaction). Many risk factors have been identified in various studies, but no great success has been seen in intervention studies (5,6). It looks as if regional musculoskeletal pain problems are here to stay, and are perhaps a ubiquitous part of modern working life (7,8).It has recently been proposed in a European guideline on back pain that the general nature and course of commonly experienced low back pain means that there is limited scope for preventing its incidence, and that prevention should be focused on reduction of the impact and consequences of back pain (ref. 9 and www.backpaineurope.org). This message could possibly be extended to other regional pain, such as arm pain, neck/shoulder pain, and lower limb pain.The aim of the present study was to examine the effect of work-related factors and individual and healthrelated factors on the onset of more severe musculoskelSupported by grants from the D...

Sensory feedback plays a major role in the regulation of the spinal neural locomotor circuitry in cats. The present study investigated whether sensory feedback also plays an important role during walking in 20 healthy human subjects, by arresting or unloading the ankle extensors 6 deg for 210 ms in the stance phase of gait. During the stance phase of walking, unloading of the ankle extensors significantly (P < 0·05) reduced the soleus activity by 50 % in early and mid‐stance at an average onset latency of 64 ms. The onset and amplitude of the decrease in soleus activity produced by the unloading were unchanged when the common peroneal nerve, which innervates the ankle dorsiflexors, was reversibly blocked by local injection of lidocaine (n= 3). This demonstrated that the effect could not be caused by a peripherally mediated reciprocal inhibition from afferents in the antagonist nerves. The onset and amplitude of the decrease in soleus activity produced by the unloading were also unchanged when ischaemia was induced in the leg by inflating a cuff placed around the thigh. At the same time, the group Ia‐mediated short latency stretch reflex was completely abolished. This demonstrated that group Ia afferents were probably not responsible for the decrease of soleus activity produced by the unloading. The findings demonstrate that afferent feedback from ankle extensors is of significant importance for the activation of these muscles in the stance phase of human walking. Group II and/or group Ib afferents are suggested to constitute an important part of this sensory feedback.

Aims: To quantify the relative contribution of work related physical factors, psychosocial workplace factors, and individual factors and aspects of somatisation to the onset of neck/shoulder pain. Methods: Four year prospective cohort study of workers from industrial and service companies in Denmark. Participants were 3123 workers, previously enrolled in a cross sectional study, where objective measurement of physical workplace factors was used. Eligible participants were followed on three subsequent occasions with approximately one year intervals. Outcomes of interest were: new onset of neck/shoulder pain (symptom cases); and neck/shoulder pain with pressure tenderness in the muscles of the neck/shoulder region (clinical cases). Results: During follow up, 636 (14.1%) participants reported neck/shoulder pain of new onset; among these, 82 (1.7%) also had clinical signs of substantial muscle tenderness. High shoulder repetition was related to being a future symptom case, and a future clinical case. Repetition was strongly intercorrelated with other physical measures. High job demands were associated with future status as a symptom case, and as a clinical case. A high level of distress predicted subsequent neck/shoulder pain, and neck/shoulder pain with pressure tenderness. Conclusions: High levels of distress, and physical and psychosocial workplace factors are predictors of onset of pain in the neck and/or shoulders, particularly pain with pressure tenderness in the muscles. N eck/shoulder pain is frequently reported among workers with repetitive manual tasks as well as among some service workers. The aetiology is largely unknown, and most studies so far are cross sectional. 3 Prospective studies have been conducted, and physical and psychosocial workplace factors such as neck flexion, sitting, quantitative job demands, and coworker support have been found to be risk factors for neck pain in a recent study.4 Physical work with a heavy load, awkward postures, and mental stress were related to one-year incidence of shoulder pain. 5The multifactorial and multidimensional nature of musculoskeletal pain has been the subject of several studies, which have found that psychological distress and other somatic symptoms are related to unspecific pain complaints from the neck and upper extremity. We aimed to determine the contribution of: (a) physical workplace factors, (b) psychosocial workplace factors, and (c) individual factors and symptom reporting to the onset of new neck/shoulder pain and neck/shoulder pain with pressure tenderness. METHODSThe study was conducted as a four year prospective cohort study, with yearly assessment of exposures in the workplace and simultaneous questionnaire screening and clinical examinations; fig 1 illustrates the total flow in the study. RecruitmentThe study population comprised 3123 workers from industrial and service sector settings, enrolled in 1994 and 1995.

1. The modulation of the short-latency stretch reflex during walking at different walking speeds was investigated and compared with the stretch reflex during standing in healthy human subjects. 2. Ankle joint stretches were applied by a system able to rotate the human ankle joint during treadmill walking in any phase of the step cycle. The system consisted of a mechanical joint attached to the subject's ankle joint and connected to a motor placed beside the treadmill by means of bowden wires. The weight of the total system attached to the leg of the subject was 900 g. 3. The short-latency soleus stretch reflex was modulated during a step. In the stance phase, the amplitude equaled that found during standing at matched soleus background electromyogram (EMG). In the transition from stance to swing, the amplitude was 0 in all subjects. In late swing, the stretch reflex amplitude increased to 45 +/- 27% (mean +/- SD) of the maximal amplitude in the stance phase (stretch amplitude 8 degrees, stretch velocity 250 degrees/s). 4. The onset (42 +/- 3.2 ms) and peak latencies (59 +/- 2.5 ms) of the stretch reflex did not depend on the phase in the step cycle at which the reflex was elicited. 5. When the ankle joint is rotated, a change in torque can be measured. The torque measured over the first 35 ms after stretch onset (nonreflex torque) was at a maximum during late stance, when the leg supported a large part of the body's weight, and at a minimum during the swing phase. At heel contact the nonreflex torque was 50% of its maximal value. 6. During the stance phase the maximal EMG stretch reflex had a phase lead of approximately 120 ms with respect to the maximal background EMG and a phase lead of approximately 250 ms with respect to the maximal nonreflex torque. 7. The constant latency of the stretch reflex during a step implied that the ankle extensor muscle spindles are always taut during walking. 8. The relatively high amplitude of the stretch reflex in late swing and at heel contact made it likely that the stretch reflex contributed to the activation of the ankle extensor muscles in early stance phase.

The central nervous system (CNS) takes advantage of a network of complex neural pathways and mechanisms in the control of normal human gait. One such mechanism is the use of afferent feedback from muscle, cutaneous and joint receptors. Our knowledge of the contribution of afferent information in human gait is still limited, although this has been an area of active research for many years (e.g. Dietz et al. 1985;Yang et al. 1991;Sinkjaer et al. 1996). Yang et al. (1991) and Sinkjaer et al. (1996) have shown that afferent-mediated feedback is used by the CNS in the control of gait when an unexpected stretch of the ankle extensors is imposed. More recently, Sinkjaer et al. (2000) provided evidence that during walking, up to 50 % of the background EMG from the soleus muscle can be attributed to afferent feedback. However, the relative importance of the separate afferent pathways may differ for the background locomotor EMG and the EMG that results from an imposed stretch.When the human soleus muscle is stretched in a seated subject, two distinct bursts, with average peak latencies of 59 and 86 ms are evident in the EMG (Toft et al. 1989). These bursts are often referred to as the short (SLR) and medium (MLR) reflex responses, respectively, and have also been labelled the M1 and M2 stretch reflex responses, respectively. The short latency response has an onset latency of approximately 40 ms and is attributed to monosynaptic excitation of spinal motoneurones from the large diameter group Ia afferent fibres (Taylor et al.Group II muscle afferents probably contribute to the medium latency soleus stretch reflex during walking in humans 1. The objective of this study was to determine which afferents contribute to the medium latency response of the soleus stretch reflex resulting from an unexpected perturbation during human walking.2. Fourteen healthy subjects walked on a treadmill at approximately 3.5 km h _1 with the left ankle attached to a portable stretching device. The soleus stretch reflex was elicited by applying small amplitude (~8 deg) dorsiflexion perturbations 200 ms after heel contact.3. Short and medium latency responses were observed with latencies of 55 ± 5 and 78 ± 6 ms, respectively. The short latency response was velocity sensitive (P < 0.001), while the medium latency response was not (P = 0.725).4. Nerve cooling increased the delay of the medium latency component to a greater extent than that of the short latency component (P < 0.005).5. Ischaemia strongly decreased the short latency component (P = 0.004), whereas the medium latency component was unchanged (P = 0.437).6. Two hours after the ingestion of tizanidine, an a 2 -adrenergic receptor agonist known to selectively depress the transmission in the group II afferent pathway, the medium latency reflex was strongly depressed (P = 0.007), whereas the short latency component was unchanged (P = 0.653).7. An ankle block with lidocaine hydrochloride was performed to suppress the cutaneous afferents of the foot and ankle. Neither the short (P = 0.453) nor m...