Hypotheses of peripheral and central mechanisms underlying occupational muscle pain and injury

Comparison of Physiological Effects Induced by Two Compression Stockings and Regular Socks During Prolonged Standing Work

OBJECTIVE

The goal of this study was to evaluate and compare lower-leg muscle fatigue, edema, and discomfort induced by the prolonged standing of security guards wearing regular socks and those wearing 15-20 or 20-30 mmHg compression stockings as intervention.

BACKGROUND

Compression stockings are sometimes used by individuals standing all day at work. However, quantitative evidence showing their potential benefits for lower-leg health issues in healthy individuals during real working conditions is lacking.

METHOD

Forty male security employees participated in the study. All were randomly assigned to the control or one of the two intervention groups (I15-20 or I20-30). Lower-leg muscle twitch force, volume, and discomfort ratings were measured before and after their regular 12-hr standing work shift.

RESULTS

Significant evidence of lower-leg long-lasting muscle fatigue, edema, and discomfort was observed after standing work for guards wearing regular socks. However, no significant changes were found for guards wearing either compression stockings.

CONCLUSION

In healthy individuals, compression stockings seem to attenuate efficiently the tested outcomes in the lower leg resulting from prolonged standing.

APPLICATION

Occupational activities requiring prolonged standing may benefit from 15-20 or 20-30 mmHg compression stockings. As similar benefits were observed for both levels of compression, the lower level may be sufficient.

Prolonged standing behaviour in people with joint hypermobility syndrome

Background

Joint Hypermobility Syndrome (JHS) is a rare Heritable Disorder of Connective tissue characterised by generalised joint laxity and chronic widespread pain. Joint Hypermobility Syndrome has a large impact on patients’ day to day activities, and many complain of symptoms when standing for prolonged periods. This study investigates whether people with JHS exhibit the same behaviours to deal with the effects of prolonged standing as people with equal hypermobility and no pain, and people with normal flexibility and no pain.

Methods

Twenty three people with JHS, 22 people with Generalised Joint Hypermobility (GJH), and 22 people with normal flexibility (NF) were asked to stand for a maximum of 15 min across two force-plates. Fidgets were counted and quantified using a cumulative sum algorithm and sway parameters of the quiet standing periods between fidgets were calculated.

Results

Average standing time for participants with JHS was 7.35 min and none stood for the full 15 min. All participants with GJH and NF completed 15 min of standing. There were no differences in fidgeting behaviour between any groups. There was a difference in anteroposterior sway (p = .029) during the quiet standing periods.

Conclusion

There is no evidence to suggest people with JHS exhibit different fidgeting behaviour. Increased anteroposterior-sway may suggest a muscle weakness and strengthening muscles around the ankle may reduce postural sway and potentially improve the ability to stand for prolonged periods.

Muscular and Vascular Issues Induced by Prolonged Standing With Different Work-Rest Cycles With Active or Passive Breaks

OBJECTIVE

The aim of this study was to evaluate the long-lasting motor, behavioral, physiological, and perceptual effects of prolonged standing work in three work-rest cycle conditions including passive or active rest breaks.

BACKGROUND

Muscle fatigue has been evidenced after prolonged standing work through physiological and neuromotor measures. It has been postulated that muscle fatigue induced by prolonged work could be attenuated by appropriate scheduling of work and rest periods. However, investigations in this domain remain limited.

METHOD

Thirty participants simulated standing work for 5 hr with work-rest cycles of short, medium, or long standing periods including passive or active breaks. Lower-leg muscle twitch force (MTF), muscle oxygenation, lower-leg volume, postural stability, force control, and discomfort perception were quantified on 2 days.

RESULTS

Prolonged standing induced significant changes in all measures immediately after 5 hr of work, indicating a detrimental effect in long-lasting muscle fatigue, performance, discomfort, and vascular aspects. Differences in the measures were not significant between work cycles and/or break type.

CONCLUSION

Similar physiological and motor alterations were induced by prolonged standing. The absence of difference in the effects induced by the tested work-rest cycles suggests that simply altering the work-rest cycle may not be sufficient to counteract the effects of mainly static standing work. Finally, standing for 3 hr or more shows clear detrimental effects.

APPLICATION

Prolonged standing is likely to contribute to musculoskeletal and vascular symptoms. A limitation to less than 3 hr of mostly static standing in occupational activities could avoid alterations leading to these symptoms.

Lower risk of musculoskeletal pain among patients with end-stage renal disease treated by hemodialysis: A frequency-matched retrospective cohort study

Musculoskeletal pain is experienced by 5%-14% of the general adult population, and it is highly common among patients with chronic kidney disease (CKD). Therefore, the purpose of the study was to decide the prevalent rate of musculoskeletal pain in end-stage renal disease (ESRD) patients and to analyze this relationship between myalgia and ESRD using clinical features and determinants.A total of 93,013 patients who received ESRD diagnoses during 2000 and 2010 and were followed up until December 31, 2011, were identified from the Longitudinal Health Insurance Database 2000 (LHID2000) of the National Health Research Institutes (NHRI); non-ESRD controls were also selected from the LHID2000.The results indicated that the risk of chronic musculoskeletal pain is significantly lower in the hemodialysis treated ESRD cohort (subhazard ratio = 0.52, P < .0001), despite of sex, age, or comorbidities. Older patients were discovered to be at lower risk of chronic musculoskeletal pain (subhazard ratio = 0.94, P = .0765), with those aged 40 to 64 years having the highest hazard ratios (subhazard ratio = 1.21, P < .0001), and the prevalence of chronic musculoskeletal pain in women was higher than that in men (vs female sex; subhazard ratio = 0.69, P < .0001). Kaplan-Meier analysis revealed a higher cumulative incidence of myalgia development in the non-ESRD cohort compared with the ESRD cohort (log-rank test, P < .001).Clinicians should assess the risk of chronic musculoskeletal pain in such patients and provide appropriate and timely support of hemodialysis.

A narrative review of musculoskeletal problems of the lower extremity and back associated with the interface between occupational tasks, feet, footwear and flooring

At least 50% of workers are exposed to the risk of musculoskeletal disorders (MSD) due to spending prolonged hours standing at work. There is a lack of information regarding issues with the feet, solutions to the problem, and links between MSD, feet, footwear and flooring. The present article provides a narrative review of the research in this area, based on 31 papers. Workers who stand for large proportions of the working day had a level of MSD considerably greater than a normal population. Muscle co-activation, blood pooling, muscle fatigue and individual characteristics are all associated with MSD. Altering flooring provided mixed results, while footwear appeared to have the potential to affect MSD, although the dearth of literature limited the conclusions that could be drawn. Despite their inextricable link, literature regarding the relationship between occupational tasks, MSD, footwear and flooring remains limited and future studies will benefit from rigorously designed protocols.

Le rôle joué par les fibres afférentes métabosensibles dans les mécanismes adaptatifs neuromusculaires

Les adaptations de l'organisme à l'exercice sont permises par l'ajustement de l'activité des neurones centraux qui est en partie régulée par l'activité des afférences I et II (mécanosensibles), par la mise en jeu des afférences III et IV (métabosensibles) et par les modifications du métabolisme musculaire au cours de l'exercice. Le rôle des afférences métabosensibles apparaît comme fondamental dans les mécanismes adaptatifs à l'exercice et dans la tolérance à la fatigue. Néanmoins, de nombreuses interrogations demeurent. Cette revue fait le bilan des connaissances concernant l'implication de ces afférences dans les boucles de rétrocontrôle sensori-motrices et les mécanismes d'adaptation neuromusculaire. Il semble désormais établi que l'activation des afférences métabosensibles soit à l'origine de l'adaptation cardiovasculaire et respiratoire à l'exercice. De plus, ces afférences seraient à l'origine d'un mécanisme de protection du muscle contre la fatigue en modulant la commande motrice centrale au niveau spinal et supraspinal.

Long-Term Muscle Fatigue After Standing Work

OBJECTIVE

The aims of this study were to determine long-term fatigue effects in the lower limbs associated with standing work and to estimate possible age and gender influences.

BACKGROUND

The progressive accumulation of muscle fatigue effects is assumed to lead to musculoskeletal disorders, as fatigue generated by sustained low-level exertions exhibits long-lasting effects. However, these effects have received little attention in the lower limbs.

METHOD

Fourteen men and 12 women from two different age groups simulated standing work for 5 hr including 5-min seated rest breaks and a 30-min lunch. The younger group was also tested in a control day. Muscle fatigue was quantified by electrically induced muscle twitches (muscle twitch force [MTF]), postural stability, and subjective evaluation of discomfort.

RESULTS

MTF showed a significant fatigue effect after standing work that persisted beyond 30 min after the end of the workday. MTF was not affected on the control day. The center of pressure displacement speed increased significantly over time after standing work but was also affected on the control day. Subjective evaluations of discomfort indicated a significant increase in perception of fatigue immediately after the end of standing work; however, this perception did not persist 30 min after. Age and gender did not influence fatigue.

CONCLUSION

Objective measures show the long-term effects of muscle fatigue after 5 hr of standing work; however, this fatigue is no longer perceived after 30 min of rest postwork.

APPLICATION

The present results suggest that occupational activities requiring prolonged standing are likely to contribute to lower-extremity and/or back disorders.

Neuromuscular responses to mild-muscle damaging eccentric exercise in a low glycogen state

The aim of this study was to examine the effect of low muscle glycogen on the neuromuscular responses to maximal eccentric contractions. Fourteen healthy men (22 ± 3 years) performed single-leg cycling (20 min at ~75% maximal oxygen uptake (V̇O2 max); eight 90 s sprints at a 1:1 work-to-rest ratio (5% decrements from 90% to 55% V̇O2 max until exhaustion) the evening before 100 eccentric (1.57 rads(-1)) with reduced (RED) and normal glycogen (NORM). Neuromuscular responses were measured during and up to 48 h after with maximal voluntary and involuntary (twitch, 20 Hz and 50 Hz) isometric contractions. During eccentric contractions, peak torque decreased (RED: -16.1 ± 2.5%; NORM: -6.2 ± 5.1%) and EMG frequency increased according to muscle length. EMG activity decreased for RED only. After eccentric contractions, maximal isometric force was reduced up to 24h for NORM (-13.5 ± 5.8%) and 48 h for RED (-7.4 ± 10.9%). Twelve hours after eccentric contractions, twitch force and the 20:50 Hz ratio were decreased for RED but not for NORM. Immediate involuntary with prolonged voluntary force loss suggests that reduced glycogen is associated with increased susceptibility to mild muscle-damaging eccentric exercise with contributions of peripheral and central mechanisms to be different during recovery.

Myofascial pain syndrome treatments

Myofascial pain syndrome (MPS) is a regional pain disorder caused by taut bands of muscle fibers in skeletal muscles called myofascial trigger points. MPS is a common disorder, often diagnosed and treated by physiatrists. Treatment strategies for MPS include exercises, patient education, and trigger point injection. Pharmacologic interventions are also common, and a variety of analgesics, antiinflammatories, antidepressants, and other medications are used in clinical practice. This review explores the various treatment options for MPS, including those therapies that target myofascial trigger points and common secondary symptoms.

Protein differences between human trapezius and vastus lateralis muscles determined with a proteomic approach

Background

The trapezius muscle is a neck muscle that is susceptible to chronic pain conditions associated with repetitive tasks, commonly referred to as chronic work-related myalgia, hence making the trapezius a muscle of clinical interest. To provide a basis for further investigations of the proteomic traits of the trapezius muscle in disease, two-dimensional difference gel electrophoresis (2D-DIGE) was performed on the healthy trapezius using vastus lateralis as a reference. To obtain as much information as possible from the vast proteomic data set, both one-way ANOVA, with and without false discovery rate (FDR) correlation, and partial least square projection to latent structures with discriminant analysis (PLS-DA) were combined to compare the outcome of the analysis.

Results

The trapezius and vastus lateralis showed significant differences in metabolic, contractile and regulatory proteins, with different results depending on choice of statistical approach and pre-processing technique. Using the standard method, FDR correlated one-way ANOVA, 42 protein spots differed significantly in abundance between the two muscles. Complementary analysis using immunohistochemistry and western blot confirmed the results from the 2D-DIGE analysis.

Conclusions

The proteomic approach used in the present study combining 2D-DIGE and multivariate modelling provided a more comprehensive comparison of the protein profiles of the human trapezius and vastus lateralis muscle, than previously possible to obtain with immunohistochemistry or SDS-PAGE alone. Although 2D-DIGE has inherent limitations it is particularly useful to comprehensively screen for important structural and metabolic proteins, and appears to be a promising tool for future studies of patients suffering from chronic work related myalgia or other muscle diseases.

On functional motor adaptations: from the quantification of motor strategies to the prevention of musculoskeletal disorders in the neck-shoulder region

BACKGROUND

Occupations characterized by a static low load and by repetitive actions show a high prevalence of work-related musculoskeletal disorders (WMSD) in the neck-shoulder region. Moreover, muscle fatigue and discomfort are reported to play a relevant initiating role in WMSD.

AIMS

To investigate relationships between altered sensory information, i.e. localized muscle fatigue, discomfort and pain and their associations to changes in motor control patterns.

MATERIALS & METHODS

In total 101 subjects participated. Questionnaires, subjective assessments of perceived exertion and pain intensity as well as surface electromyography (SEMG), mechanomyography (MMG), force and kinematics recordings were performed.

RESULTS

Multi-channel SEMG and MMG revealed that the degree of heterogeneity of the trapezius muscle activation increased with fatigue. Further, the spatial organization of trapezius muscle activity changed in a dynamic manner during sustained contraction with acute experimental pain. A graduation of the motor changes in relation to the pain stage (acute, subchronic and chronic) and work experience were also found. The duration of the work task was shorter in presence of acute and chronic pain. Acute pain resulted in decreased activity of the painful muscle while in subchronic and chronic pain, a more static muscle activation was found. Posture and movement changed in the presence of neck-shoulder pain. Larger and smaller sizes of arm and trunk movement variability were respectively found in acute pain and subchronic/chronic pain. The size and structure of kinematics variability decreased also in the region of discomfort. Motor variability was higher in workers with high experience. Moreover, the pattern of activation of the upper trapezius muscle changed when receiving SEMG/MMG biofeedback during computer work.

DISCUSSION

SEMG and MMG changes underlie functional mechanisms for the maintenance of force during fatiguing contraction and acute pain that may lead to the widespread pain seen in WMSD. A lack of harmonious muscle recruitment/derecruitment may play a role in pain transition. Motor behavior changed in shoulder pain conditions underlining that motor variability may play a role in the WMSD development as corroborated by the changes in kinematics variability seen with discomfort. This prognostic hypothesis was further, supported by the increased motor variability among workers with high experience.

CONCLUSION

Quantitative assessments of the functional motor adaptations can be a way to benchmark the pain status and help to indentify signs indicating WMSD development. Motor variability is an important characteristic in ergonomic situations. Future studies will investigate the potential benefit of inducing motor variability in occupational settings.

Effects of graduated compression stockings with different pressure profiles on lower-limb venous structures and haemodynamics

INTRODUCTION

Graduated compression stockings (GCS) are one of the essential mechanical therapeutic approaches used in prevention and treatment of venous diseases. Pressure levels and gradient distribution are the two determined parameters influencing the performance of GCS products. However, the effects of GCS with different pressure profiles on venous function remain controversial in practical use.

OBJECTIVE

To determine the physiological effects of GCS with different pressure levels and gradient distribution profiles on the venous function of the lower extremities.

METHODS

At specific testing points along the long and short saphenous veins (LSV, SSV) and popliteal veins (PV) of the lower extremities, Doppler ultrasound techniques were used to examine venous cross-sectional areas (VA, cm(2)), the venous peak blood flow (PVpeak, cm/sec) and venous mean blood flow (PVmean, cm/sec) velocities in twelve female subjects wearing GCS with varying pressure profiles in a controlled laboratory environment. The Doppler examination was conducted three times during the 4-hour period (after wearing GCS for 1 minute, 70 minutes, and 170 minutes) in each subject.

RESULTS

The pressure levels of GCS and duration of wear had statistically significant influences on the venous anatomy and venous haemodynamics. GCS with light, mild, moderate and strong pressures increased the popliteal PVpeak by 9.64%, 25.74%, 29.91% and 26.47%, respectively, and significantly decreased the VA. The GCS maintained these venous haemodynamics over time. No significant differences in blood flow were found between the mild, moderate and strong pressure GCS.

CONCLUSION

The application of GCS with light and mild compression profiles appear to be effective in achieving a reduction in venous dilation and venous pooling, and improving venous return in the lower extremities. GCS with lighter pressures may be more suitable for subjects whose daily work requires long-term inactive standing or sitting, and GCS with mild pressure appear to be sufficient for most clinical applications.

Society, mind and body in chronic fatigue syndrome: an anthropological view

An anthropological view of chronic fatigue syndrome places the study of illness in social context. Data from an interview study of 50 chronically fatigued patients demonstrate the relation of local social worlds--families, workplaces, communities--to the meaning and experience of illness. Negative life events and difficulties, multiple commitments, and a hectic pace are among prominent themes in the subjects' local worlds. These themes are reflected in: (1) attributions of illness onset to social sources, (2) the symbolism of the core complaint of fatigue, and (3) an illness-induced, positively valued lifestyle transformation suggesting the rejection of culturally prescribed 'busyness'. Dichotomous definitions of the relation of mind and body are shown to be part of culture, not Nature, in the paper's second section. The 'mind-body dichotomy' and the differing values attached to physical and psychological disorders by a naturalistic scientific paradigm explain the delegitimizing experiences of sufferers, who find their illness dismissed as psychosomatic and therefore 'not real'. A conceptualization of chronic fatigue syndrome which links local social worlds to psychological distress, felt bodily sensation and biological changes is proposed. Collaborative teams of social scientists and medical researchers might fruitfully pursue aspects of social context in relation to psychiatric, immunological and viral dimensions of the illness.

Therapie bei Schmerzen der Kaumuskulatur

Myalgias of the masticatory muscles are the most frequent noninfectious complaints in the orofacial region. After summarizing the current knowledge on the physiology, etiology, pathophysiology, diagnosis, and differential diagnosis of masticatory muscle pain, we specifically focus on management recommendations. Results of an extensive literature search show that for the majority of patients pain reduction or pain relief can be achieved with noninvasive reversible methods. Longitudinal short- and long-term studies have revealed that different therapeutic measures are similarly effective. In patients with chronic masticatory myalgias associated with psychosocial impairment, however, additional involvement of a psychotherapist is crucial.

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.

Factors contributing to officers' fatigue in high-speed maritime craft operations

The purpose of this study was to investigate the difference in the level of fatigue induced by high-speed maritime craft operation between the day- and night-shift officers. The demographic and work-related factors that contribute to fatigue were also explored. A total of 93 high-speed maritime craft officers participated in the survey, of whom 35 worked a day shift (Mean age=48.3 years) and 58 worked a night shift (Mean age=45.8 years). Fatigue experience was measured with the Chinese version of the Swedish Occupational Fatigue Inventory (SOFI-C) at the beginning, in the middle and at the end of the work shift. Information on age, work experience, perceived voyage difficulty and duty schedule was obtained. The study found that the night-shift officers seemed to manifest an overall higher level of perceived fatigue than the day-shift officers, while the day-shift officers demonstrated a fatigue carry-over effect across the two workdays. Besides the shift pattern, age, experience in operating high-speed maritime craft and perceived voyage difficulty were the significant factors contributing to the officers' fatigue experience. The finding that the fatigue experience associated with high-speed maritime craft operation has a rapid and accumulative nature suggests that different occupational safety and health guidelines should be devised for these two groups of officers.

Effect of low-level laser (Ga-Al-As 655 nm) on skeletal muscle fatigue induced by electrical stimulation in rats

We investigated whether low-level laser therapy (LLLT) can reduce muscular fatigue during tetanic contractions in rats. Thirty-two male Wistar rats were divided into four groups receiving either one of three different LLLT doses (0.5, 1.0, and 2.5 J/cm2) or a no-treatment control group. Electrical stimulation was used to induce six tetanic muscle contractions in the tibial anterior muscle. Contractions were stopped when the muscle force fell to 50% of the initial value for each contraction (T50%). There was no significant difference between the 2.5 J/cm2 laser-irradiated group and the control group in mean T50% values. Laser-irradiated groups (0.5 and 1.0 J/cm2) had significantly longer T50% values than the control group. The relative peak force for the sixth contraction in the laser-irradiated groups were significantly higher at 92.2% (SD 12.6) for 0.5 J/cm2, 83.2% (SD 20.5) for 1.0 J/cm2, and 82.9% (SD 18.3) for 2.5 J/cm2 than for the control group [50% (SD 15)]. Laser groups receiving 0.5 and 1.0 J/cm2 showed significant increases in mean performed work compared with both the control group and their first contraction values. Muscle damage was indirectly measured by creatine kinase levels in plasma. A distinct dose-response pattern was found in which 1.0 and 2.5 J/cm2 LLLT groups had significantly lower creatine kinase levels than the 0.5 J/cm2 LLLT group and the control group. We conclude that LLLT doses of 0.5 and 1.0 J/cm2 can prevent development of muscular fatigue in rats during repeated tetanic contractions.

Repeated static contractions increase mitochondrial vulnerability toward oxidative stress in human skeletal muscle

Repeated static contractions (RSC) induce large fluctuations in tissue oxygen tension and increase the generation of reactive oxygen species (ROS). This study investigated the effect of RSC on muscle contractility, mitochondrial respiratory function, and in vitro sarcoplasmic reticulum (SR) Ca(2+) kinetics in human muscle. Ten male subjects performed five bouts of static knee extension with 10-min rest in between. Each bout of RSC (target torque 66% of maximal voluntary contraction torque) was maintained to fatigue. Muscle biopsies were taken preexercise and 0.3 and 24 h postexercise from vastus lateralis. Mitochondria were isolated and respiratory function measured after incubation with H(2)O(2) (HPX) or control medium (Con). Mitochondrial function was not affected by RSC during Con. However, RSC exacerbated mitochondrial dysfunction during HPX, resulting in decreased respiratory control index, decreased mitochondrial efficiency (phosphorylated ADP-to-oxygen consumed ratio), and increased noncoupled respiration (HPX/Con post- vs. preexercise). SR Ca(2+) uptake rate was lower 0.3 vs. 24 h postexercise, whereas SR Ca(2+) release rate was unchanged. RSC resulted in long-lasting changes in muscle contractility, including reduced maximal torque, low-frequency fatigue, and faster torque relaxation. It is concluded that RSC increases mitochondrial vulnerability toward ROS, reduces SR Ca(2+) uptake rate, and causes low-frequency fatigue. Although conclusive evidence is lacking, we suggest that these changes are related to increased formation of ROS during RSC.

Treatment of Fibromyalgia, Myofascial Pain, and Related Disorders

Chronic muscle pain is a common complaint among patients who seek care for musculoskeletal disorders. A spectrum of clinical presentations exists, ranging from focal or regional complaints that usually represent myofascial pain syndromes to more wide spread pain that may meet criteria for a diagnosis of fibromyalgia. This article addresses the epidemiology, pathophysiology, and clinical management of myofascial pain syndrome and fibromyalgia. These conditions are challenging to treat and require physiatrists to be aware of the wide range of pharmacologic, rehabilitative,and psychosocial interventions that can be helpful.

Interaction of biomechanical and morphological factors on shoulder workload in industrial paint work

BACKGROUND

It is known that work-related musculoskeletal disorders are caused by multifactor operations of various risk factors. Among these, the association of these risk factors with pain symptoms and work-related musculoskeletal disorders have been reported in many studies in all typical manufacturing settings (Bernard, 1997). This study focuses on the automobile industry.

METHODS

Twenty-nine paint area production workers of an automobile industry plant took part (age 37.7+/-8.2 years; seniority 6.9+/-6.2 years). Musculoskeletal morbidity was assessed through a questionnaire-administered interview and a clinical exam. Each workplace exposure was assessed by the observational rapid upper limb assessment method. The quantification of the workload on shoulders and wrists during the actual work task accomplishment was obtained through surface EMG.

FINDINGS

Biomechanical exposure varied significantly between pain symptomatic and asymptomatic workers. It was the only estimator that could predict the risk of occurrence of musculoskeletal symptoms. Multifactor linear analysis showed that some linear and combined anthropometric characteristics could be associated to a higher workload on the shoulders and upper limbs.

INTERPRETATION

The rigid external working conditions for employees with different morphologic characteristics, combined with demanding force application associated with the adoption of awkward postures for long and continuous periods of work time, impose constraints in accomplishment of the paint tasks. Additionally our results suggest that the same work task could present different musculoskeletal mechanical load for people with different anthropometrics.

Age-related changes in human postural control of prolonged standing

The aim of this study was to characterize prolonged standing and its effect on postural control in elderly individuals in comparison to adults. It is unknown how elderly individuals behave during prolonged standing and how demanding such a task is for them. We recorded the center of pressure (COP) position of 14 elderly subjects and 14 adults while they performed prolonged standing (30 min) and quiet stance tasks (60s) on a force plate. The number and amplitude of the COP patterns, the root mean square (RMS), speed, and frequency of the COP sway were analyzed. The elderly subjects were able to stand for prolonged periods but they produced postural changes of lesser amplitude and a decreased sway during the prolonged standing task. Both the adults and the elderly subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS and COP speed in the quiet standing trial after the prolonged standing task, in comparison to the trial before. We suggest that the lack of mobility in elderly subjects may be responsible for the observed sub-optimal postural changes in this group. The inability of elderly individuals to generate similar responses to adults during prolonged standing may contribute to the increased risk of falls in the older population.

Pathophysiology of upper extremity muscle disorders

A review of the literature on the pathophysiology of upper extremity muscle disorders (UEMDs) was performed. An overview is given of clinical findings and hypotheses on the pathogenesis of UEMDs. The literature indicates that disorders of muscle cells and limitations of the local circulation underlie UEMDs. However, these disorders identified do not necessarily lead to symptoms. The following mechanisms have been proposed in the literature: (1) selective recruitment and overloading of type I (Cinderella) motor units; (2) intra-cellular Ca(2+) accumulation; (3) impaired blood flow; (3b) reperfusion injury; (3.3c) blood vessel-nociceptor interaction; (4a) myofascial force transmission; (4b) intramuscular shear forces; (5) trigger points; (6) impaired heat shock response. The results of the review indicate that there are multiple possible mechanisms, but none of the hypotheses forms a complete explanation and is sufficiently supported by empirical data. Overall, the literature indicates that: (1) sustained muscle activity, especially of type I motor units, may be a primary cause of UEMDs; (2) in UEMDs skeletal muscle may show changes in morphology, blood flow, and muscle activity; (3) accumulation of Ca(2+) in the sarcoplasm may be the cause of muscle cell damage; (4) it seems plausible that suboptimal blood flow plays a role in pathogenesis of UEMDs; (5) since the presence of fiber disorders is not a sufficient condition for the development of UEMSDs additional mechanisms, such as sensitization, are assumed to play a role.

Physical Exposures in Work Commonly Done by Women

The North American workforce is still highly sex-segregated, with most members of each sex in jobs composed primarily of workers of the same sex. This division is accentuated when jobs involve physical demands. Women have traditionally been assigned to tasks whose physical demands are considered to be light. Nevertheless, these tasks can have biological effects, sometimes serious. Phenomena related to physical demands of women's work can be considered in three categories: (a) musculoskeletal and cardiovascular demands of tasks often assigned to women in factories and service work; (b) sex- and gender-specific effects of toxic substances found in the workplace; and (c) interactions between work and the domestic responsibilities of many women. These phenomena are described, using examples recently gathered from workplaces. Effects of biological sex are distinguished, as far as possible, from effects of gender (social roles). Keywords: ergonomics, gender, occupation, anthropometry, toxicity, repetitive movements, static effort

Métabosensibilité musculaire et adaptations physiologiques au cours de l’exercice

The first role played by group III (thin myelinated) and group IV (unmyelinated) afferent fibres from skeletal muscle is to transmit nociceptive information from muscle to the central nervous system. The second role of these free endings located in the interstitium of the muscle is to induce cardiovascular and respiratory adjustments during muscular exercise. These respiratory and circulatory responses during muscular exercise may be reflexly induced via muscular afferents. Indeed, static contraction of hindlimb muscles in anaesthetised mammals has been shown to reflexly increase the ventilatory function, the myocardial contractility and heart rate. The mechanical muscle deformation and the accumulation of metabolites in its intersitium are the cause of raised activity in small nerve fibres which in turn induces the physiological responses. It is also admitted that the central locomotor areas on the medullary and spinal neuronal pools control ventilatory and cardiovascular function during exercise. This mechanism is called "central command". Furthermore, adjustments of the locomotor activity during exercise is mediated by the thinly myelinated and unmyelinated fibres with endings in the working muscle. These fibres, also called "metaboreceptor" may be responsible of the coupling between the ventilation and the locomotion. Thickly myelinated muscle afferents (i.e. group I and II) appear to play little role in causing the reflex autonomic responses to contraction.

L, Marcos RL, Lopes-Martins RAB. Avaliação do ácido láctico intramuscular através da espectroscopia Raman: novas perspectivas em medicina do esporte

O uso da espectroscopia Raman no infravermelho pode vir a constituir uma nova técnica para avaliação física, permitindo medidas da concentração de ácido láctico em sangue e em músculo esquelético, por um método não invasivo. A espectroscopia Raman é uma técnica que oferece grande riqueza de detalhes provida pela vibração de moléculas em diferentes níveis de energia. Em estudos prévios, foram obtidos espectros Raman de ácido láctico em plasma humano e em sangue de rato, onde os picos característicos foram observados claramente na matriz biológica. No presente estudo a espectroscopia Raman foi usada para a identificação de ácido láctico em músculo tibial de rato. Foi usado um laser de Ti:safira sintonizado em 830nm, um espectrômetro Kaiser f/l.8 e um detector de CCD refrigerado. O espectro Raman do ácido láctico apresenta oito picos bem distintos, entre 700 e 1.500cm-1, correspondendo aos diferentes modos de vibração da molécula do ácido láctico. O pico principal em 830cm-1 foi usado para caracterizar a presença do ácido láctico no músculo tibial de rato. Foram analisados espectros Raman de músculos tibiais in vivo e in vitro. Além disso, também foi monitorada a difusão do ácido láctico através do músculo, in vitro. Pode-se concluir, a partir dos resultados obtidos, que a espectroscopia Raman no infravermelho próximo apresenta grande potencial para, no futuro, com o aperfeiçoamento da técnica, ser utilizada em avaliações físicas com o intuito de permitir medições das concentrações de ácido láctico no músculo esquelético, através de metodologia não invasiva.

Masseter thickness, endurance and exercise-induced pain in subjects with different vertical craniofacial morphology

The aim of the study was to compare neuromuscular features of the masseter muscle in subjects with different vertical craniofacial morphology. Fifteen short-faced (mandibular plane-Frankfurt plane angle < 15 degrees) and 15 normal- to long-faced (mandibular plane-Frankfurt plane angle > or = 23 degrees) male students participated. The thickness of the masseter was assessed by ultrasonography. Onset and endurance of exercise pain were recorded during sustained biting at a level of 15% of maximum voluntary contraction and 30 micro V electromyographic activity. Pain and fatigue was measured on visual analog scales before and after the biting, as well as before and after 10 min chewing. Statistical comparison showed that the masseter muscle was significantly thicker (+15%) in the short-faced than the normal- to long-faced subjects. The pain onset time and endurance time were also consistently shorter in short-faced subjects, whereas the intensity of pain and fatigue did not differ significantly between the two groups. Multiple stepwise regression showed positive influence from the mandibular plane inclination and the masseter thickness on the pain onset time and endurance time. The present findings support the concept that subjects with different craniofacial morphology show neuromuscular differences.

Muscle pain in athletes with locomotor disability

PURPOSE

Athletes with locomotor disabilities (LDA) participate in many competitive sport activities, yet little is known about sport-related muscle pain (SRMP). This study assessed the prevalence, determinants, and main characteristics of SRMP in LDA.

METHODS

A cross-disability epidemiological survey was used to investigate the occurrence of SRMP during the previous year by using a questionnaire administrated by medical doctors. SRMP was defined as any muscle pain experienced during the past 12 months that either occurred during sport activity (training or competition) and/or was reported as a consequence of physical exercise, causing discomfort for at least 1 d and not related to systemic disease. A total of 227 LDA were recruited randomly from the population (567 LDA) who participated in selected National sports events (including swimming, athletics, wheelchair basketball matches, and others) organized by the Italian Federation of Sports for Disabled. Collected data were statistically analyzed with univariate and multivariate logistic regression models to identify possible determinants of SRMP, through the estimate of the prevalence odds ratios.

RESULTS

The SRMP period prevalence rate was equal to 50.7% (95% confidence interval (44.0-57.4%)), ranging from 47.0% (swimmers) to 58.8% (basketball athletes). In 71.1% of cases, SRMP lasted less than 1 wk and only 8.7% experienced pain for more than 1 month. SRMP had a higher prevalence in amputees (75.0%) and spinal cord injured LDA (58.1%) than the other groups. There was increased prevalence rate of SRMP with increased training volume. The multivariate logistic regression model showed disorder type, body mass index, and training volume as determinants of SRMP.

CONCLUSIONS

Prospective studies could be devised to assess the role of anthropometric characteristics and training volume as risk factors of SRMP.

A comparison of the effects of floor mats and shoe in-soles on standing fatigue

In assembly line positions and other occupations, employees experience pain and discomfort associated with long periods of standing. Modifying flooring is a common intervention method used to alleviate problems associated with constrained standing. This study investigated the effects of four different standing conditions upon assembly workers' perception of general fatigue and discomfort associated with various body parts following 1 week of 8-h days of exposure to each condition. The four standing conditions were (1) on hard floor, (2) on a floor mat, (3) wearing shoe in-soles, and (4) wearing shoe in-soles while standing on a floor mat. Questions were asked regarding general fatigue and discomfort. In general, the mat, in-soles and combined conditions were more comfortable than standing on hard floor. Moderately strong correlations were found for the variables of height, age and job tenure. Shorter individuals experienced greater discomfort in the upper leg and low back when standing on a mat and when wearing in-soles. The older workers and those with more job seniority reported greater discomfort associated with body joints when standing on the hard floor and when standing on the floor mat. No significant differences in fatigue or discomfort were found when comparing the overall effects of using the floor mat to wearing the shoe in-soles or the combined condition.

Short-Term Effects of Workstation Exercises on Musculoskeletal Discomfort and Postural Changes in Seated Video Display Unit Workers

Background and Purpose. In recent years, a number of exercise programs have been developed for computer operators in order to promote movement and to reduce musculoskeletal discomfort. Tests of the effectiveness of these exercise programs, especially in field trials, are rare. The authors tested the hypothesis that doing regular, short-term (&lt;10 days) exercises while at a workstation would decrease musculoskeletal discomfort and increase in-chair movement (ICM). Subjects. Eleven directory assistance operators (8 female, 3 male) with no recent history of musculoskeletal problems volunteered. Methods. In-chair movement was measured by tracking the center of pressure at the buttock-chair interface as subjects sat on a pressure-sensitive mat. Musculoskeletal discomfort was rated through the use of the Body Part Discomfort Scale (BPDS) and a body map. We used a revised Dataspan exercise program. Operators were tested for 2 hours, on 2 occasions: before and after doing exercises for 3- to 5-day shifts. During each test, ICM was measured during three 15-minute periods at the start of the test and at the end of hours 1 and 2. Subjects rated musculoskeletal discomfort per body part using the BPDS at 30, 60, and 120 minutes of each test. The effects of exercises on ICM and BPDS ratings were examined with a two-way repeated-measures analysis of variance with day (2) × time (3) designs. Results. When subjects were doing their exercises, ICM was higher at the start and hour 1, and perceived discomfort was lower during each test period (start, hour 1, and hour 2). When not exercising, subjects' musculoskeletal discomfort increased over time and was higher during all test periods. Discussion and Conclusion. Exercises done by video display unit operators while at a workstation resulted in short-term decreases in both musculoskeletal discomfort and postural immobility. These results suggest that workstation exercises may be beneficial.

Focused review: myofascial pain

Myofascial pain is defined as pain that originates from myofascial trigger points in skeletal muscle. It is prevalent in regional musculoskeletal pain syndromes, either alone or in combination with other pain generators. The appropriate evaluation and management of myofascial pain is an important part of musculoskeletal rehabilitation of regional axial and limb pain syndromes. This article reviews the current hypotheses regarding the pathophysiology of myofascial trigger points and muscle pain. A critical evidence-based review of the pharmacologic, nonpharmacologic, alternative medicine, and exercise treatments of myofascial pain is provided, as well as future research directions. OVERALL LEARNING OBJECTIVE: To review critically the state of the art knowledge of myofascial pain, including pathophysiology and comprehensive management. Areas of future research are identified.

Effect of topical heat on electromyographic power density spectrum in subjects with myofascial pain and normal controls: a pilot study

OBJECTIVE

To investigate the influence of superficial heat on the fatigue cascade of the upper trapezius muscle in subjects with myofascial pain and matched normal controls.

DESIGN

In a prospective randomized block crossover pilot study, eight female subjects, ages 20-35 yr, with upper trapezius muscle trigger points and eight matched female control subjects without pain were studied. Subjects performed six 100-sec shoulder shrug contractions to fatigue, with subjects randomly chosen to receive heat during the first three or last three trials. The initial median frequency and the slope of the median frequency decline were calculated from the data.

RESULTS

In the subjects with pain, the slope of the median frequency was elevated in ambient room temperature as compared with controls. There was no difference in slope of the median frequency under heated conditions. Heat application in controls before fatiguing exercise caused an increase in initial median frequency, whereas exercise before heat treatment resulted in a significantly lower initial median frequency. Subjects with myofascial pain had no significant change in initial median frequency.

CONCLUSIONS

Heat seems to have a positive effect on muscle function in normal individuals when applied before exercise. Subjects with myofascial pain respond differently to exercise and heat challenge, which suggests a difference in their muscle physiology.

Colour Doppler sonographic analysis of blood-flow velocity in the human facial artery and changes in masseter muscle thickness during low-level static contraction

Muscle oedema, which can be seen as a thickness increment by ultrasonography, is important in provoking pain and fatigue during low-level contraction. Although oedema is related to the balance of inflow and outflow of blood, there are no data on the correlation between muscle thickness change and blood-flow. Blood-flow velocities in the facial artery and the muscle thickness changes were measured by colour Doppler ultrasonography in 30 healthy volunteers during 20 min contraction with 10% of maximum force. Thickness and velocity changes both reached a peak in the initial phase of contraction. The initial change of thickness did not correlate with the velocity in the facial artery, while those immediately after exercise showed a high correlation. The velocity changes in the facial artery might depend on both the general response to contraction and local metabolic or mechanical factors in the contracted masseters.

Ischemia causes muscle fatigue

The purpose of this investigation was to determine whether ischemia, which reduces oxygenation in the extensor carpi radialis (ECR) muscle, causes a reduction in muscle force production. In eight subjects, muscle oxygenation (TO2) of the right ECR was measured noninvasively and continuously using near infrared spectroscopy (NIRS) while muscle twitch force was elicited by transcutaneous electrical stimulation (1 Hz, 0.1 ms). Baseline measurements of blood volume, muscle oxygenation and twitch force were recorded continuously, then a tourniquet on the upper arm was inflated to one of five different pressure levels: 20, 40, 60 mm Hg (randomized order) and diastolic (69 +/- 9.8 mm Hg) and systolic (106 +/- 12.8 mm Hg) blood pressures. Each pressure level was maintained for 3-5 min, and was followed by a recovery period sufficient to allow measurements to return to baseline. For each respective tourniquet pressure level, mean TO2 decreased from resting baseline (100% TO2) to 99 +/- 1.2% (SEM), 96 +/- 1.9%, 93 +/- 2.8%, 90 +/- 2.5%, and 86 +/- 2.7%, and mean twitch force decreased from resting baseline (100% force) to 99 +/- 0.7% (SEM), 96 +/- 2.7%, 93 +/- 3.1%, 88 +/- 3.2%, and 86 +/- 2.6%. Muscle oxygenation and twitch force at 60 mm Hg tourniquet compression and above were significantly lower (P < 0.05) than baseline value. Reduced twitch force was correlated in a dose-dependent manner with reduced muscle oxygenation (r = 0.78, P < 0.001). Although the correlation does not prove causation, the results indicate that ischemia leading to a 7% or greater reduction in muscle oxygenation causes decreased muscle force production in the forearm extensor muscle. Thus, ischemia associated with a modest decline in TO2 causes muscle fatigue.

Standing and very slow walking: foot pain-pressure threshold, subjective pain experience and work activity

Prolonged standing is described as uncomfortable by exposed workers, but the discomfort has not been linked to precise descriptions of workplace activity. We observed 10 sales and kitchen workers ("group 1") who worked standing. We compared the plantar pain-pressure threshold (PPT) of "group 1" (10 standing workers) to that of "group 2" (11 researchers who could choose their posture freely). Group 1 spent an average time of 62% standing still compared to 5% for group 2. Despite the fact that group 1 were primarily confined to defined areas and stood for 62% of the time, their mean time standing still was only 7 s. They walked 35% of the time, but 57% of walking sequences were only one or two steps. Group 1 PPT declined by 23% over the work day compared to 5% among group 2 (p < 0.05, ANOVA). Foot PPT is a promising quantitative indicator of effects of standing work.

Influence of compression hosiery on physiological responses to standing fatigue in women

PURPOSE

The purpose of this investigation was to examine the influence of various designs of commercial hosiery, which use graduated compression, on the physiological and performance responses to standing fatigue.

METHODS

Twelve healthy women (age = 23.0+/-2.1 yr, height = 165.7+/-5.0 cm, percent body fat = 22.6+/-4.2%, body mass = 60.0+/-8.9 kg) volunteered to participate in this investigation. All subjects completed four identical standing fatigue protocols with different garment conditions each separated by 7 d. The standing fatigue protocol involved a total of 8 h of standing on hard floors during which subjects participated in various tasks and experimental testing procedures. In addition, all activity and dietary profiles of the subjects were carefully controlled 48 h before each experimental session. Before the standing fatigue protocol, subjects completed a battery of tests to establish morning baseline values. Experimental tests included determination of lower leg venous cross-sectional area, blood pressure, heart rate, perceived discomfort ratings, circumferences measurements, total body water, variation in center of pressure during "quiet" standing, vertical jump performance, and specific regional patterns of foot pressures.

RESULTS

This investigation demonstrated that commercial hosiery with various forms of graduated compression and construction were effective in mediating a reduction in edema in the ankles and legs while reducing the amount of venous pooling and discomfort in the lower body. Different constructions of garments may mediate these overall effects via different physiological mechanisms related to fluid shifts and muscle tissue damage.

CONCLUSION

Wearing various types of graduated compression hose during the day as it relates to women in standing professions may minimize edema and muscle tissue disruption, thereby increasing comfort in the legs.

The prevalences of cytochrome c oxidase negative and superpositive fibres and ragged-red fibres in the trapezius muscle of female cleaners with and without myalgia and of female healthy controls

The association of cytochrome c oxidase negative fibres (COX-negative) and ragged-red fibres (RR-fibres) with work related trapezius myalgia has been proposed. Hitherto studies have been small or without control groups. The aim of the present study was to investigate the prevalences of RR-fibres and COX-negative fibres in female cleaners with (n=25) and without (n=23) trapezius myalgia and in clinically healthy female teachers (n=21). The cleaners did mainly floor cleaning requiring monotonous loading on the trapezius muscle. A questionnaire covering background data and aspects of pain (prevalence, duration, intensity and influence on daily living) was answered. Biopsies were obtained from the trapezius muscle by an open surgical technique. The three groups did not differ in prevalence of COX-negative or COX-superpositive (i.e. type-I fibres with extremely strong brownish reaction in both the COX and SDH/COX stainings) fibres. The prevalence of COX-negative fibres was age dependent. Two subgroups of RR-fibres were present when stained for COX; COX-negative (73%) and COX-superpositive (26%) fibres. Forty-two percent of the COX-negative fibres were RR-fibres and 79% of the COX-superpositive were RR-fibres. A significantly (P=0.002) higher proportion of the COX-superpositive fibres in the cleaners were RR-fibres compared to the teachers. Multivariate regression analysis revealed that age, occupation as cleaner and a tender point in the trapezius were significantly associated with increased prevalences of RR-fibres; a cleaner with a tender point had a 4.35 higher prevalence of RR-fibres compared to a teacher without a tender point. No correlations between other pain related variables and prevalence of RR-fibres were noted. In conclusion, RR-fibres but not COX-negative or COX-superpositive fibres were correlated with cleaning work tasks and with a tender point in the trapezius.

Is fibromyalgia a distinct clinical entity? Pain mechanisms in fibromyalgia syndrome. A myologist's view

The cause of muscle pain and allodynia may not be the same in all persons fulfilling the American College of Rheumatology (ACR) criteria for fibromyalgia syndrome. In the majority of patients the generalized pain is preceded by localized or regional pain, usually in the musculoskeletal system. In many patients with fibromyalgia there are findings compatible with tissue injury pain with pain mechanisms involving both the primary afferent neuron and the nociceptive system in the central nervous system. Evidence for these mechanisms is described.

Hormonal pertubations in fibromyalgia syndrome

The symptomatology characterizing fibromyalgia (FM) comprises three systems: the musculoskeletal system with widespread muscular pain, neuroendocrine disorders, and psychological distress including depression. Though the most prominent symptom of FM is pain in defined points of the musculoskeletal system, the numerous other somatoform and psychological disorders suppose a common primary disturbance which we consider to originate within higher levels of the central nervous system. Recent studies of the entire endocrine profile of FM patients following a simultaneous challenge of the hypophysis with corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone, growth hormone-releasing hormone, and luteinizing hormone-releasing hormone support the hypothesis that an elevated activity of CRH neurons determines not only many symptoms of FM but may also cause the deviations observed in the other hormonal axes. Hypothalamic CRH neurons thus may play a key role not only in "resetting" the various endocrine loops but possibly also nociceptive and psychological mechanisms as well.

Mechanically corrected EMG for the continuous estimation of erector spinae muscle loading during repetitive lifting

Few studies have been carried out on the changes in biomechanical loading on low-back tissues during prolonged lifting. The purpose of this paper was to develop a model for continuously estimating erector spinae muscle loads during repetitive lifting and lowering tasks. The model was based on spine kinematics and bilateral lumbar and thoracic erector spinae electromyogram (EMG) signals and was developed with the data from eight male subjects. Each subject performed a series of isometric contractions to develop extensor moments about the low back. Maximum voluntary contractions (MVCs) were used to normalize all recorded EMG and moment time-histories. Ramp contractions were used to determine the non-linear relationship between extensor moments and EMG amplitudes. In addition, the most appropriate low-pass filter cut-off frequencies were calculated for matching the rectified EMG signals with the moment patterns. The mean low-pass cut-off frequency was 2.7 (0.4) Hz. The accuracy of the non-linear EMG-based estimates of isometric extensor moment were tested with data from a series of six rapid contractions by each subject. The mean error over the duration of these contractions was 9.2 (2.6)% MVC. During prolonged lifting sessions of 20 min and of 2 h, a model was used to calculate changes in muscle length based on monitored spine kinematics. EMG signals were first processed according to the parameters determined from the isometric contractions and then further processed to account for the effects of instantaneous muscle length and velocity. Simple EMG estimates were found to underestimate peak loading by 9.1 (4.0) and 25.7 (11.6)% MVC for eccentric and concentric phases of lifting respectively, when compared to load estimates based on the mechanically corrected EMG. To date, the model has been used to analyze over 5300 lifts.