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The shoulder region is a common site of work-related musculoskeletal disorders. Biomechanical models may reveal the relative importance of force, joint-moments, and angular velocity for predicting muscle activity, thereby contributing to identify risk factors.The aim of the present study was to predict muscle activity patterns from joint kinetics during cleaning work and to identify the most important variables requesting muscle activity.Design. A comparative study of six cleaners performing five different floor cleaning tasks (combinations of tool and working method) in a laboratory setting.Net forces and moments at the glenohumeral joint were estimated using a video-based 3D link segment model together with 3D force-transducers at each hand, separately. Angular velocities of the upper arm were calculated, and electromyographic activity was recorded bilaterally from the muscles trapezius, deltoideus, and infraspinatus.The biomechanical model revealed abduction moment in the glenohumeral joint to be the most important factor for development of muscle activity in m. deltoideus and m. infraspinatus, while for m. trapezius vertical force was most important.Muscle specific determinants for shoulder muscle activity could be identified from glenohumeral joint kinetics.This study documents that mechanical work requirements in terms of joint forces, moments of force and angular velocities can predict major fractions of muscle activity patterns in the upper extremities. The biomechanical model used for this prediction revealed different factors of importance for individual muscles. This knowledge is fundamental for work place interventions aiming at minimizing overloading of specific muscles to prevent or rehabilitate muscle disorders.

The purpose of the study was to characterize the sarcoplasmic reticulum (SR) function and contractile properties before and during recovery from fatigue in the rat extensor digitorum longus muscle. Fatiguing contractions (60 Hz, 150 ms/s for 4 min) induced a reduction of the SR Ca2+release rate to 66% that persisted for 1 h, followed by a gradual recovery to 87% of prefatigue release rate at 3 h recovery. Tetanic force and rate of force development (+dF/d t) and relaxation (−dF/d t) were depressed by ∼80% after stimulation. Recovery occurred in two phases: an initial phase, in which during the first 0.5–1 h the metabolic state recovered to resting levels, and a slow phase from 1–3 h characterized by a rather slow recovery of the mechanical properties. The recovery of SR Ca2+release rate was closely correlated to +dF/d t during the slow phase of recovery ( r2= 0.51; P < 0.05). Despite a slowing of the relaxation rate, we did not find any significant alterations in the SR Ca2+uptake function. These data demonstrate that the Ca2+release mechanism of SR is sensitive to repetitive in vitro muscle contraction. Moreover, the results indicate that +dF/d t to some extent depends on the rate of Ca2+release during the slow phase of recovery.

BACKGROUND: Flight-related neck/shoulder pain is frequent among military helicopter pilots and crew members. With a lifetime prevalence of 81 % for pilots and 84 % for crew members, the prevalence of neck pain is considered high compared to the general population. The aim of this study was to investigate whether a specifically tailored exercise intervention would reduce the prevalence and incidence rate of neck/shoulder pain among helicopter pilots and crew members.METHOD: This study used a prospective, parallel group, single blinded, randomized controlled design. Participants were military helicopter pilots and crew members recruited from the Royal Danish Air Force. Inclusion criteria were: 1) employed within the Royal Danish Air Force as a helicopter pilot or onboard crew member (technician, systems-operator, tactical helicopter observer and/or navigator), 2) maintaining operational flight status at enrollment, and 3) operational flying within the previous 6 months. Primary outcome was change in neck and shoulder pain assessed by 1) a modified version of the "Standardized Nordic questionnaire for the analysis of musculoskeletal symptoms" and by 2) pressure pain threshold measurements. Secondary outcomes included: postural balance, strength, stability, and rate of force development for neck and shoulder muscles. Measurements at baseline and follow-up were conducted at four air force bases in Denmark. Sixty-nine participants were individually randomized to either a training group (TG) or a reference group (RG). Participants in the TG performed 20-weeks of physical exercise training divided into sessions of 3 × 20 min per week. Training was completed within working hours and consisted of specific exercise training for the neck and shoulder muscles based on the principles of "Intelligent Physical Exercise Training". The RG received no training.DISCUSSION: In spite of the high prevalence of flight related neck/shoulder pain among military helicopter pilots and crew members there are currently no evidence based guidelines for the prevention or clinical handling of neck pain among these occupational groups. Results from this study may therefore be beneficial for future establishment of such guidelines.TRIAL REGISTRATION: Ethical committee of Southern Denmark (S-20120121) 29 August, 2012. Clinical Trail Registration ( NCT01926262 ) 16 August, 2013.

PHYSICAL WORKLOAD ON NECK AND SHOULDER MUSCLES DURING MILITARY HELICOPTER FLIGHTMurray M, 1, Lange B, 2, Olsen H.B, 1, Søgaard K, 1, Sjøgaard G, 11Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, DK2Department of Anesthesia and Intensive Care Medicine, Odense University Hospital, DKE-mail: mmurray@health.sdu.dkAIM: Flight-related neck/shoulder pain is common among military helicopter pilots and crew members. During flight, the flight helmet and additional Night Vision Goggles (NVG) pose a considerable load on the cervical spine. The aim of this study was to quantify the physical workload on the cervical muscles during flight with and without NVG. METHODS: Nine pilots and nine crew members participated in this study. Before a flight, one pilot and one crew member were equipped with 6 wireless electromyography sensors, positioned bilaterally above trapezius m. (TRA), the upper neck extensors (UNE) and sternocleido-mastoid m. (SCM). Nine repetitive flights were completed, encompassing: Patient-Transport (PT), Patient-Transport with NVG (PT+NVG) and Search And Rescue with NVG (SAR+NVG). A standard helmet (1.85 kg) and NVG (1.1 kg) were used. The EMG signal was normalized using Maximal Voluntary Contractions (MVC) and analyzed for changes in amplitude and distribution of muscle activity by an Amplitude Probability Distribution Function (APDF). RESULTS: MVC for shoulder elevation (right/left) was: 136.8±41.3 / 120.6±47.0 Nm, and for cervical-flexion and extension: 32.2±14.0 and 42.5±10.2 Nm. EMG sampling time was: 16.9±5.1 min for PT, 22.7±10.8 min for PT+NVG and 21.3±11.1 min for SAR+NVG. Mean muscle activity (%MVE) in UNE was significantly higher than TRA and SCM during all flights, except for crew members during PT. UNE showed significantly higher %MVE during SAR+NVG compared to PT or PT+NVG for pilots. An APDF analysis showed that UNE during SAR+NVG was significantly higher than TRA and SCM, during 10% (APDF 0.1), 50% (APDF 0.5) and 90% (APDF 0.9) of total flight time.CONCLUSION: Muscle activity in the upper neck muscles was high with an overall level of 10% MVE or above for half of total flight-time. This high level of sustained muscle activity may indicate a risk for developing neck disorders among helicopter crew and pilots.

Background: Previous studies have shown positive effects of physical exercise at the workplace on musculoskeletal disorders. However, long-term adherence remains a challenge. The present study evaluates long-term adherence and effects of a workplace strength training intervention on back, neck and upper extremity pain among laboratory technicians. Methods. Cluster-randomized controlled trial involving 537 industrial laboratory technicians. Subjects were randomized at the cluster level to one of two groups: training group 1 (TG1, n = 282) performing supervised strength training from February to June 2009 (round one) or training group 2 (TG2, n = 255) performing supervised strength training from August to December 2009 (round two). The outcome measures were changes in self-reported pain intensity (0-9) in the back, neck and upper extremity as well as Disability of the Arm, Shoulder and Hand (DASH, 0-100). Results: Regular adherence, defined as at least one training session per week, was achieved by around 85% in both groups in the supervised training periods. In the intention-to-treat analyses there were significant group by time effects for pain in the neck, right shoulder, right hand and lower back and DASH - resulting in significant reductions in pain (mean 0.3 to 0.5) and DASH (mean 3.9) in the scheduled training group compared to the reference group. For TG1 there were no significant changes in pain in round two, i.e. they maintained the pain reduction achieved in round one. Subgroup analyses among those with severe pain (> = 3 on a scale of 0-9) showed a significant group by time effect for pain in the neck, right shoulder, upper back and lower back. For these subgroups the pain reduction in response to training ranged from 1.1 to 1.8. Conclusions: Specific strength training at the workplace can lead to significant long-term reductions in spinal and upper extremity pain and DASH. The pain reductions achieved during the intensive training phase with supervision appears to be maintained a half year later.

Udgivelsesdato: 2010-Feb PURPOSE: The aim of the present study is to examine the association between physical activity and perceived job demand, job control, perceived stress and energy, and physiological arousal reflected by morning and evening concentrations of cortisol in saliva among white-collar workers. METHODS: Physical activity during the last week was assessed during work and leisure time by a Danish version of the International Physical Activity Questionnaire and saliva samples were collected. The study group comprised 389 white-collar workers, aged 25-67 years, and of which 257 were women. RESULTS: We found that physical activity during leisure time was associated with higher perceived energy, and for men also with lower perceived stress. Further, we found that physical activity at leisure time affected the association between salivary cortisol and perceived stress and energy so that respondents being physically active at leisure time and perceiving higher energy showed higher evening saliva cortisol. CONCLUSION: Physically active employees perceive less stress and more energy. The association between stress-energy and salivary cortisol was affected by vigorous physical activity. No association between job control-demand and the degree of physical activity was found. Based on the present data, we recommend office workers-exposed to high job strain and inactivity at the job-to perform physical activity, preferably of high intensity, in order to reduce stress and increase energy.

Sodium, potassium, and magnesium were analyzed in human slow-twitch (ST) and fast-twitch (FT) skeletal muscles. In contrast to other species, no relation was found between fiber composition and electrolyte distribution. In soleus (S), vastus lateralis (VL), and triceps brachii (TB) the overall mean values for 6 men and 6 women were 44 mmol K/100 g dry wt and 11 mmol Na/100 g dry wt; the intracellular concentrations were 161 mmol K/l and 26 mmol Na/l with no differences between the muscles. Analysis of fragments of single ST and FT fibers from each of the muscles also showed no difference between the fiber types in Na and K content. Small differences were seen between the muscles with regard to Mg, but these were not related to fiber composition compared with other species. During exercise to exhaustion (3 bouts of bicycling for 3 min at 325-395 W, 6 men) the extracellular electrolyte concentrations for Na, K, and Mg increased from 134 to 140, 4.5 to 5.8, and 0.75 to 0.87 mmol/l, respectively (P less than 0.05). In VL Na content increased from 9.8 to 16.5 mmol/100 g dry wt, while intracellular [Na] remained constant. In contrast, intracellular [K] decreased from 161 to 141 mmol/l (P less than 0.05). No such changes occurred in TB. In concert with other studies the present changes in electrolytes in the working muscles indicate that muscle fatigue may be related to changes at the muscle fiber membrane.

BACKGROUND: Health promotion at the work site in terms of physical activity has proven positive effects but optimization of relevant exercise training protocols and implementation for high adherence are still scanty.METHODS/DESIGN: The aim of this paper is to present a study protocol with a conceptual model for planning the optimal individually tailored physical exercise training for each worker based on individual health check, existing guidelines and state of the art sports science training recommendations in the broad categories of cardiorespiratory fitness, muscle strength in specific body parts, and functional training including balance training. The hypotheses of this research are that individually tailored worksite-based intelligent physical exercise training, IPET, among workers with inactive job categories will: 1) Improve cardiorespiratory fitness and/or individual health risk indicators, 2) Improve muscle strength and decrease musculoskeletal disorders, 3) Succeed in regular adherence to worksite and leisure physical activity training, and 3) Reduce sickness absence and productivity losses (presenteeism) in office workers. The present RCT study enrolled almost 400 employees with sedentary jobs in the private as well as public sectors. The training interventions last 2 years with measures at baseline as well as one and two years follow-up.DISCUSSION: If proven effective, the intelligent physical exercise training scheduled as well as the information for its practical implementation can provide meaningful scientifically based information for public health policy.TRIAL REGISTRATION: ClinicalTrials.gov, number: NCT01366950.

Upper limb disorders (ULDs) are common, and so are the difficulties in specific diagnoses of these disorders. Prior studies have shed light on the nerves in the diagnostic approach beside disorders related to muscles, tendons and joints (MCDs).The study aimed to compare the distribution of upper limb disorders, and the vibration perception threshold (VPT) in different diagnostic groups according to 1) A-criteria: the SALTSA consensus criteria, including MCDs and four peripheral neuropathies, and 2) B-criteria: including MCDs and 10 different neuropathy diagnoses--re-defined in an attempt to refine diagnostic criteria of peripheral neuropathy in respect of different MCDs; and further to discuss the impact of the presented criteria.161 patients--recruited from 21 general practitioners--were examined by the same examiner according to the two sets of diagnostic criteria. VPT measurements were conducted in all patients.Three patients did not fulfill the criteria of any ULD diagnosis. A/B criteria were fulfilled for 181/183 upper limbs, respectively, out of which 29.3%/163.3% were neuropathy diagnoses alone, 23.8%/10.9% MCD alone, and 46.9%/25.7% were categorized as neuropathy in combination with MCD diagnoses. The overall agreement on presence of neuropathy was high (75%), but on focal level there was a large discrepancy. According to the A-criteria, patients with symptoms located at wrist and shoulder were primarily defined with wrist diagnoses, and only few had concomitant shoulder diagnoses. In contrast, the B-criteria primarily defined neuropathy located at the shoulder, often concomitantly with neuropathy of the radial and the median nerve at the elbow, but seldom at the wrist level. In MCDs defined by both sets of criteria--Rotator cuff syndrome and medial/lateral epicondylitis--the A-criteria defined more MCDs than the B-criteria, the B diagnoses typically constituted only a part of the A diagnoses and additionally defined neuropathy. The B-criteria showed more significant VPT findings than the A-criteria concerning the discrimination between limbs with and contralateral limbs without diagnoses as well as between diagnostic groups with and without neuropathy.The VPT findings suggest the B-criteria to be superior to A-criteria for differentiating between patients with and without neuropathy. This study shows that neuropathy is extensive in ULDs when specific diagnostic criteria are used. Additionally it suggests the importance of a critical revision of the current diagnostic criteria of upper limb neuropathy, and the differential diagnoses concerning the MCDs. Management and prevention is highly dependent on correct diagnoses.

IntroductionNeck and shoulder pain is a common complaint among fighter pilots and a growing aero-medical concern. Unfortunately, previous intervention studies have been unsuccessful in relieving such pain within this occupational group. The aim of this study was to investigate if an exercise intervention could reduce the high prevalence of neck pain among fighter pilots.MethodsF-16 pilots were randomized in a controlled intervention trial, to either an exercise-training-group (ET, n=27) or reference-group (REF, n=28). ET underwent 24 weeks of strength, endurance, and coordination training, 3 times a week, targeting deep and superficial neck muscles (see: www.sdu.dk/f16pilots). REF received no training but was scheduled for corresponding training 6 months later. Main outcome: Three months prevalence of neck pain assessed on a ten point visual analog scale, VAS (0 corresponded to “no pain” and 10 to “pain at worst”). Compliance was evaluated by training diary as mean training sessions completed per week, and by questionnaire on a six-step scale, 1) regular, 2-3 times a week, 2) less regular, 1-2 times a week, 3) irregular, but > 4 times a month, 4) very irregular, 2-3 times a month, 5) seldom, trained but stopped, 6) no participation at all. Maximal Voluntary Isometric Contraction (MVC) and Rate of Force Development (RFD) for cervical flexion and extension were measured by strain-gauge transducers. ResultsPrevalence of neck pain was significantly reduced in ET from baseline (mean ± SD) 2.0 ± 0.4 to follow-up 1.0 ± 0.2, change -1.0 ± 0.4 (P = 0.01), but not in REF from 2.1 ± 0.4 to 2.3 ± 0.4 (P = 0.80). Comparison between groups found the reduction significant (P = 0.01). Compliance for ET according to the training diary was 1.9 ± 0.6 times per week, and according to questionnaire 58% participated more that once a week (scale 1+2). Compliance according to the questionnaire correlated with registrations in the training diary (r = -0.745, P = < 0.000). MVC measures for cervical flexion and extension at baseline in ET were 183.6 N ± 47.1 and 286.5 N ± 48.0, and in REF 160.7 N ± 51.4 and 265.2 N ± 60.8, respectively. No significant differences were found between groups at follow-up for cervical flexion or extension. RFD for cervical-flexion increased significantly in ET from 866.6 N/s ± 263.5 at baseline to 968.9 N/s ± 295.9 at follow-up (P = 0.04), but not in the REF group, from 807.0 N/s ± 286.2 to 867.8 N/s ± 274.3 (P = 0.33). No difference was found between groups at follow-up. DiscussionThe exercise intervention reduced neck pain among F-16 pilots with a modest effect size. Compliance according to the questionnaire correlated well with participation based on the training diary, but only 58% of the training group trained regularly once or more a week. Higher compliance may be requested to attain strength gain and larger effect size. The intervention incorporated deep neck muscle training, which may be an important factor in the success of the training regime.

Muscle fatigue - defined as impaired contractility - coincided in rat skeletal muscle during in vitro experiments with a decrease in intracellular potassium concentration, [K], and a decrease in resting membrane potential, RMP. In man changes in intra- and extracellular electrolyte concentrations and RMP were calculated from muscle biopsies and blood samples during voluntary contractions. At exhaustion in maximal exercise the intracellular [K] decreased by 20-40 mM from a resting value of 165 mM. Simultaneously extracellular [K] increased by 1-2 mM, and also the intra- as well as extracellular [Na] tended to increase. The calculated RMP therefore decreased from a resting value of -89 mV to -75 mV. During prolonged submaximal exercise similar changes occurred although the rate of these changes was slower. The K lost from the exercising muscles was being taken up by other tissues, and during recovery the fatigued muscles regain the previously lost K.the K-gradient across the muscle membrane decreased significantly during maximal as well as submaximal exercise. At exhaustion this change is of an order of magnitude, which may well impair the excitability of the muscle membrane and thereby the contractility of the muscle fibres.

Interstitial potassium concentration, [K+], is modulated during muscle activity due to a number of different mechanisms: diffusion and active transport of K+ in combination with water fluxes. The relative significance of the various mechanisms for muscle function is quantified. The effect of interstitial [K+] locally on the single muscle fiber is discussed along with its effect on the cardiovascular and respiratory systems and its role in motor control. It is concluded that K+ may play a significant role in the prevention as well as the development of fatigue.

Work-related musculoskeletal disorders cause chronic pain and functional impairment, impose heavy costs on society, and reduce productivity. In this position paper from the Scientific Committee for Musculoskeletal Disorders of the ICOH, the most important risk factors at work are described. Work-related musculoskeletal disorders have high incidences and prevalences among workers who are exposed to manual handling, repetitive and static work, vibrations, and poor psychological and social conditions. The application of ergonomic principles in the workplace is the best method for prevention. International organizations should develop standards, common classifications, and terminologies. Surveillance systems should be further developed nationally and in workplaces, and more effort should be directed to information dissemination, education, and training.