Association between occupational lifting and day-to-day change in low-back pain intensity based on company records and text messages.

Objective This study aimed to investigate the association between occupational lifting and day-to-day change in low-back pain (LBP) intensity. Methods Each day for three consecutive weeks, 95 full-time workers from 51 Danish supermarkets with frequent occupational lifting replied to daily text messages about LBP intensity (scale 0-10). Supervisors at the supermarkets provided information about daily working hours and load (number of different pallets handled) for each worker during the three weeks. Linear mixed models with repeated measures tested the association between variables controlled for LBP during the previous day and various confounders. Results Workers handled on average 1212 [standard deviation (SD) 861] kg and worked 8.5 (SD 1.8) hours per workday. LBP intensity was higher in the morning after work- compared with non-workdays [difference of 0.55, 95% confidence interval (95% CI) 0.39-0.71]. A cumulative effect of consecutive workdays existed, ie, pain intensity increased approximately 0.30 points per day for up to three days. For three consecutive work- compared with non-workdays, the difference was 0.92 (95% CI 0.50-1.34). Higher load resulted in higher pain intensity in the morning after workdays [0.16 (95% CI 0.02-0.31) per ton lifted], while no effect was found for number of daily working hours. Conclusion Among workers with frequent occupational lifting, workdays are associated, in a cumulative manner, with increased LBP intensity. Furthermore, an exposure-response association exists between workload and increased LBP intensity. However, the increase in pain intensity was small and future studies should assess whether long-term consequences exist.

Physical workload and risk of long-term sickness absence in the general working population and among blue-collar workers: prospective cohort study with register follow-up.

OBJECTIVE: To determine the prospective association between physical workload--in terms of specific physical exposures and the number of exposures--and long-term sickness absence (LTSA). METHODS: Using cox-regression analyses, we estimated the risk of register-based incident LTSA (at least 3 consecutive weeks) from self-reported exposure to different physical workloads among 11,908 wage earners from the general working population (Danish Work Environment Cohort Study year 2000 and 2005). RESULTS: The incidence of LTSA was 8.9% during two-year follow-up. Spending 25% or more of the total work time with a bent or twisted back (HR 1.59 (95% CI 1.39 to 1.83)), arms above shoulder height (HR 1.35 (95% CI 1.14 to 1.59)), squatting or kneeling (HR 1.30 (95% CI 1.09 to 1.54)), pushing/pulling or lifting/carrying (HR 1.40 (95% CI 1.22 to 1.62)) and standing in the same place for 50% or more of total work time (HR 1.19 (95% CI 1.00 to 1.42), were risk factors for LTSA when adjusted for baseline age, gender, psychosocial work environment, lifestyle, musculoskeletal and mental disorders, and socioeconomic status. HR increased from 1.25 (95% CI 1.04 to 1.51) for one to 1.94 (95% CI 1.56 to 2.41) for four combined physical workloads. Results largely remained stable in subgroup analyses including only blue-collar workers (n=5055). Population attributable risks for LTSA from one or more physical workloads were 26% and 40% in the general working population and among blue-collar workers, respectively. CONCLUSIONS: Several of the investigated types of physical workload were risk factors for LTSA when exceeding 25% of the work time. A higher number of combined physical workloads was associated with progressively increased risk. Our study underscores the importance of physical workload as risk factors for LTSA in the general working population as well as among blue-collar workers.

Straight ladder inclined angle in a field environment: the relationship among actual angle, method of set-up and knowledge.

Ladder inclined angle is a critical factor that could lead to a slip at the base of portable straight ladders, a major cause of falls from heights. Despite several methods established to help workers achieve the recommended 75.5° angle for ladder set-up, it remains unclear if these methods are used in practice. This study explored ladder set-up behaviours in a field environment. Professional installers of a company in the cable and other pay TV industry were observed for ladder set-up at their worksites. The results showed that the actual angles of 265 ladder set-ups by 67 participants averaged 67.3° with a standard deviation of 3.22°. Although all the participants had training on recommended ladder set-up methods, only 3 out of 67 participants applied these methods in their daily work and even they failed to achieve the desired 75.5° angle. Therefore, ladder set-up remains problematic in real-world situations. Practitioner Summary: Professional installers of a cable company were observed for portable straight ladder set-up at their worksites. The ladder inclined angle averaged 67.3° with a standard deviation of 3.22°, while the recommended angle is 75.5°. Only a few participants used the methods that they learned during training in their daily work.

Does rare use of assistive devices during patient handling increase the risk of low back pain? A prospective cohort study among female healthcare workers.

PURPOSE: To investigate whether rare use of assistive devices during patient handling increases the respective risk for infrequent and frequent low back pain (LBP) among female healthcare workers reporting to be free of LBP at baseline. METHOD: Female healthcare workers replied to questionnaires about use of assistive devices during patient handling activities (rarely, occasionally and often) and LBP in both 2005 and 2006. Among those reporting to be free of LBP (0 days the past 12 months) in 2005 (n = 1,478), the multi-adjusted odds ratio for developing infrequent LBP (1-30 days the past 12 months) and frequent LBP (>30 days the past 12 months) in 2006 depending on use of assistive devices was prospectively investigated. RESULTS: The multi-adjusted odds ratio for developing infrequent LBP was 1.21 (95 % CI 0.90-1.62) for those occasionally using assistive devices, and 1.78 (95 % CI 1.19-2.66) for those rarely using assistive devices, referencing healthcare workers often using assistive devices during patient handling (p < 0.01 for trend). No associations between use of assistive devices during patient handling and risk of frequent LBP were found. CONCLUSION: The study indicates that rare use of assistive devices can increase the risk for developing infrequent LBP in female healthcare workers reporting to be free from LBP at baseline.

Effect of grip type, wrist motion, and resistance level on pressures within the carpal tunnel of normal wrists.

Elevated carpal tunnel pressure (CTP) has been associated with carpal tunnel syndrome. This study systematically evaluated the effect of wrist motion resistance and grip type on CTP during wrist motion typical of occupational tasks. CTP during four wrist motion patterns, with and without resistance, and with and without gripping, was measured in vivo in 14 healthy individuals. CTP measured during compound motions fell between that measured in the cardinal planes of wrist flexion/extension and radial/ulnar deviation. Generally, with no active gripping there was little pressure change due to wrist angular displacement or resistance level. However, concurrent active pinch or power grip increased CTP particularly in motions including extension. CTP typically did not increase during wrist flexion, and in fact often decreased. Extension motions against resistance when employing a pinch or power grip increase CTP more than motions with flexion. Results could help inform design or modification of wrist motion intensive occupational tasks. © 2014 The Authors.

Patient transfers and assistive devices: prospective cohort study on the risk for occupational back injury among healthcare workers.

OBJECTIVES: This prospective cohort study investigates work-related risk factors for occupational back injury among healthcare workers. METHODS: The study comprised 5017 female healthcare workers in eldercare from 36 municipalities in Denmark who responded to a baseline and follow-up questionnaire in 2005 and 2006, respectively. Using logistic regression, the odds for occupational back injury (ie, sudden onset episodes) in 2006 from patient transfers in 2005 was modeled. RESULTS: In the total study population, 3.9% experienced back injury during follow-up, of which 0.5% were recurrent events. When adjusting for lifestyle (body mass index, leisure-time physical activity, smoking), work-related characteristics (seniority and perceived influence at work), and history of back pain and injury, daily patient transfers increased the risk for back injury (trend, P=0.03): odds ratio (OR) 1.75 [95% confidence interval (95% CI) 1.05-2.93] for 1-2 transfers per day, OR 1.81 (95% CI 1.14-2.85) for 3-10 transfers per day, and OR 1.56 (95% CI 0.96-2.54) for >10 transfers per day, referencing those with <1 patient transfer on average per day. The population attributable fraction of daily patient transfer for back injury was estimated to be 36%. Among those with daily patient transfer (N=3820), using an assistive device decreased the risk for back injury for "often" and "very often" use [OR 0.59 (95% CI 0.36-0.98) and OR 0.62 (95% CI 0.38-1.00), respectively] referencing those who "seldom" use assistive devices. CONCLUSION: Daily patient transfer was associated with increased risk for back injury among healthcare workers. Persistent use of an assistive device was associated with reduced risk for back injury among healthcare workers with daily patient transfers.

The effect of handle design on upper extremity posture and muscle activity during a pouring task.

In this study, the effect of container handle parameters on shoulder and upper limb muscle activity and joint posture during a pouring task is investigated. Results indicated that a low handle position and a vertical handle slope minimised the loading of the shoulder muscles. A high and sloped handle minimised the muscle activity and wrist deviation of the lower arm. The effects of diameter were not significant for most dependent variables during the lifting phase of the task; however, beneficial effects were seen with the smallest handle diameter during the pouring phase. A trade-off existed between the shoulder and the hand/wrist posture with the different handles. The findings of significance with relatively small effect size suggest a high sensitivity of the system to any changes. In the real world, speed, space and work conditions are important factors that influence how a task is performed. This emphasises the importance of proper handle design. PRACTITIONER SUMMARY: In this study, the effect of container handle design on the muscle activity and postures of the upper extremity during a pouring task were analyzed using the experimental data collected from electromyography and motion tracking systems. The low handle height and vertical handle slope design yielded the lowest shoulder muscle activity.

Specificity of back muscle response to submaximal fatiguing contractions.

A fatigue-related decrease in quality and accuracy of the proprioceptive feedback from muscle spindles in the back (e.g. stretch reflexes) may lead to a deterioration of spinal stability, thereby making the spine more vulnerable to external perturbations. Endurance time, tissue oxygenation, reflex latency and blood pressure response were studied in twenty subjects during a submaximal endurance test of the back extensors (20 % MVC) performed as either a position task (supporting a weight stack while maintaining trunk position) or a force task (exerting a force against a dynamometer). Mean endurance time was 8.91 (± 2.79) min for the force task and 10.86 (± 6.93) min for the position task. This result is in striking contrast to what has previously been reported from limb muscles, and suggests that back muscles are especially well suited for postural tasks. An increased reflex latency found after the position task indicates that the disadvantage of the prolonged endurance time is a deterioration of the afferent input from the muscle spindles that may potentially hamper the protection of the spine.

Risk factors for neck and upper extremity disorders among computers users and the effect of interventions: an overview of systematic reviews.

BACKGROUND: To summarize systematic reviews that 1) assessed the evidence for causal relationships between computer work and the occurrence of carpal tunnel syndrome (CTS) or upper extremity musculoskeletal disorders (UEMSDs), or 2) reported on intervention studies among computer users/or office workers. METHODOLOGY/PRINCIPAL FINDINGS: PubMed, Embase, CINAHL and Web of Science were searched for reviews published between 1999 and 2010. Additional publications were provided by content area experts. The primary author extracted all data using a purpose-built form, while two of the authors evaluated the quality of the reviews using recommended standard criteria from AMSTAR; disagreements were resolved by discussion. The quality of evidence syntheses in the included reviews was assessed qualitatively for each outcome and for the interventions. Altogether, 1,349 review titles were identified, 47 reviews were retrieved for full text relevance assessment, and 17 reviews were finally included as being relevant and of sufficient quality. The degrees of focus and rigorousness of these 17 reviews were highly variable. Three reviews on risk factors for carpal tunnel syndrome were rated moderate to high quality, 8 reviews on risk factors for UEMSDs ranged from low to moderate/high quality, and 6 reviews on intervention studies were of moderate to high quality. The quality of the evidence for computer use as a risk factor for CTS was insufficient, while the evidence for computer use and UEMSDs was moderate regarding pain complaints and limited for specific musculoskeletal disorders. From the reviews on intervention studies no strong evidence based recommendations could be given. CONCLUSIONS/SIGNIFICANCE: Computer use is associated with pain complaints, but it is still not very clear if this association is causal. The evidence for specific disorders or diseases is limited. No effective interventions have yet been documented.

Comparison of two self-reported measures of physical work demands in hospital personnel: a cross-sectional study.

BACKGROUND: Low back pain (LBP) is a frequent health complaint among health care personnel. Several work tasks and working postures are associated with an increased risk of LBP. The aim of this study was to compare two self-reported measures of physical demands and their association with LBP (the daily number of patient handling tasks and Hollmann's physical load index). METHODS: A questionnaire was distributed to 535 hospital employees in a psychiatric and an orthopedic ward in a Danish hospital. Of these 411 (77%) filled in and returned the questionnaire. Only the 373 respondents who had non-missing values on both measures of physical demands were included in the analyses. The distribution of physical demands in different job groups and wards are presented, variance analysis models are employed, and logistic regression analysis is used to analyze the association between measures of physical demands and LBP. RESULTS: In combination, hospital ward and job category explained 56.6% and 23.3% of the variance in the self-reported physical demands measured as the daily number of patient handling tasks and as the score on the physical load index, respectively. When comparing the 6% with the highest exposure the prevalence odds ratio (POR) for LBP was 5.38 (95% CI 2.03-14.29) in the group performing more than 10 patient handling tasks per day and 2.29 (95% CI 0.93-5.66) in the group with the highest score on the physical load index. CONCLUSION: In specialized hospital wards the daily number of patient handling tasks seems to be a more feasible measure of exposure when assessing the risk of LBP compared to more advanced measures of physical load on the lower lumbar spine.

Back muscle response to sudden trunk loading can be modified by training among healthcare workers.

STUDY DESIGN: Experimental study of the effect of physical training on the reaction to sudden back loading. OBJECTIVE: To investigate the effect and sustainability of "on the job training" on the reaction to sudden back loading among employees at a geriatric ward. SUMMARY OF BACKGROUND DATA: Available data suggest that a delayed muscle reflex response to sudden trunk loading may increase the risk of low back injuries. We have previously shown that training may alter the response to sudden trunk loading in healthy subjects and decrease the time elapsed until stopping of the forward movement of the trunk (stopping time). Data on the possibilities of a training-induced improvement in the reflex response among workers exposed to sudden trunk loading on the job are, however, nonexistent, and there is no evidence of long-term benefits, i.e., the sustainability of a positive training effect. METHODS: The study included 23 participants and 14 controls. All were healthy without prior history of low back pain (LBP). The training group participated in a total of 18 training sessions during a 9-week period. The training focused on reactions to a variety of sudden trunk loadings. Before and after the training intervention and at a 1-year follow-up, all subjects were tested for their reaction to expected and unexpected sudden trunk loading by applying a horizontal force of 58 N to the upper back of the subjects and measuring the electromyographic (EMG) response from the erector spinae muscles. RESULTS: In the training group, the stopping time and the distance moved after unexpected sudden trunk loading decreased significantly (13%-19%, P = 0.02). The improved stopping time was associated with marked changes in the time-wise distribution of the EMG signal after training. In addition, the follow-up study showed a high sustainability of the training effect. CONCLUSIONS: The results demonstrated a training-induced improvement of the response to sudden trunk loading that may be beneficial in workers, such as nurses, who are exposed to sudden trunk perturbations during patient handling.

Lumbar position sense acuity during an electrical shock stressor.

BACKGROUND: Optimal motor control of the spine depends on proprioceptive input as a prerequisite for co-ordination and the stability of the spine. Muscle spindles are known to play an important role in proprioception. Animal experiments suggest that an increase in sympathetic outflow can depress muscle spindle sensitivity. As the muscle spindle may be influenced by sympathetic modulation, we hypothesized that a state of high sympathetic activity as during mental stress would affect the proprioceptive output from the muscle spindles in the back muscles leading to alterations in proprioception and position sense acuity. The aim was to investigate the effect of mental stress, in this study the response to an electrical shock stressor, on position sense acuity in the rotational axis of the lumbar spine. METHODS: Passive and active position sense acuity in the rotational plane of the lumbar spine was investigated in the presence and absence of an electrical shock stressor in 14 healthy participants. An electrical shock-threat stressor lasting for approximately 12 minutes was used as imposed stressor to build up a strong anticipatory arousal: The participants were told that they were going to receive 8 painful electrical shocks however the participants never received the shocks. To quantify the level of physiological arousal and the level of sympathetic outflow continuous beat-to-beat changes in heart rate (beats x min(-1)) and systolic, diastolic and mean arterial blood pressure (mmHg) were measured. To quantify position sense acuity absolute error (AE) expressed in degrees was measured. Two-way analysis of variance with repeated measurements (subjects as random factor and treatments as fixed factors) was used to compare the different treatments. RESULTS: Significant increases were observed in systolic blood pressure, diastolic blood pressure, and heart rate during the stress sessions indicating elevated sympathetic activity (15, 14 and 10%, respectively). Despite pronounced changes in the sympathetic activity and subjective experiences of stress no changes were found in position sense acuity in the rotational plane of the lumbar spine in the presence of the electrical shock stressor compared to the control period. CONCLUSION: The present findings indicate that position sense acuity in the rotational plane of the spine was unaffected by the electrical shock stressor.

Sympathetic outflow enhances the stretch reflex response in the relaxed soleus muscle in humans.

Animal experiments suggest that an increase in sympathetic outflow can depress muscle spindle sensitivity and thus modulate the stretch reflex response. The results are, however, controversial, and human studies have failed to demonstrate a direct influence of the sympathetic nervous system on the sensitivity of muscle spindles. We studied the effect of increased sympathetic outflow on the short-latency stretch reflex in the soleus muscle evoked by tapping the Achilles tendon. Nine subjects performed three maneuvers causing a sustained activation of sympathetic outflow to the leg: 3 min of static handgrip exercise at 30% of maximal voluntary contraction, followed by 3 min of posthandgrip ischemia, and finally during a 3-min mental arithmetic task. Electromyography was measured from the soleus muscle with bipolar surface electrodes during the Achilles tendon tapping, and beat-to-beat changes in heart rate and mean arterial blood pressure were monitored continuously. Mean arterial pressure was significantly elevated during all three maneuvers, whereas heart rate was significantly elevated during static handgrip exercise and mental arithmetic but not during posthandgrip ischemia. The peak-to-peak amplitude of the short-latency stretch reflex was significantly increased during mental arithmetic (P < 0.05), static handgrip exercise (P < 0.001), and posthandgrip ischemia (P < 0.005). When expressed in percent change from rest, the mean peak-to-peak amplitude increased by 111 (SD 100)% during mental arithmetic, by 160 (SD 103)% during static handgrip exercise, and by 90 (SD 67)% during posthandgrip ischemia. The study clearly indicates a facilitation of the short-latency stretch reflex during increased sympathetic outflow. We note that the enhanced stretch reflex responses observed in relaxed muscles in the absence of skeletomotor activity support the idea that the sympathetic nervous system can exert a direct influence on the human muscle spindles.

The effect of mental stress on heart rate variability and blood pressure during computer work.

The aim was to evaluate the cardiovascular and subjective stress response to a combined physical and mental workload, and the effect of rest. Twelve females who had no prior experience of laboratory experiments participated in the study. Computer-work-related mental stressors were either added to or removed from a standardized computer work session in the laboratory. Beat-to-beat blood pressure and electrocardiogram (ECG) were recorded continuously during the experiment. The participants reported subjective experiences of stress in six categories using an 11-point scale before and at the end of the work. Heart rate variability (HRV) variables were calculated from the ECG recordings, and a reduction in the high-frequency component of HRV and an increase in the low- to high-frequency ratio were observed in the stress situation compared to the control session. No changes were seen in the low-frequency component of HRV. The stressors induced an increase in blood pressure compared to baseline that persisted, and for the diastolic pressure it even increased in the subsequent control session. No differences were observed for subjective experience of stress with the exception of a time trend in the exhaustion scale, i.e. a progression in reported exhaustion with time. The results-and the dissociation between HRV and blood pressure variables-indicate that HRV is a more sensitive and selective measure of mental stress. It could be speculated that heart rate-derived variables reflect a central pathway in cardiovascular control mechanisms ("central command"), while the blood pressure response is more influenced by local conditions in the working muscles that partly mask the effect of changes in mental workloads. In the rest period after each work session, HRV and blood pressure variables were partly normalized as expected. However, an 8-min period of rest was insufficient to restore blood pressure to resting values.

Training can modify back muscle response to sudden trunk loading.

Sudden, unexpected loading to the trunk has been reported in the literature as a potential cause of low-back disorders. This study's aim was to investigate the effect of "readiness training" on the response to sudden back loading among untrained healthy individuals. The study included 19 participants and 19 matched controls. All were employees at the National Institute of Occupational Health. The participants received ten 45-min training sessions during a 4-week period. The training focused on reactions to a variety of expected and unexpected sudden trunk loadings, including balance and coordination exercises. Before and after the training, all subjects were tested for reaction to sudden trunk loading (SL). This entailed applying a horizontal force of 58 N to the subject's upper back. Elapsed time--measured between SL and stopping--decreased significantly in the training group (from 337 to 311 ms) compared with the control group. The improved stopping time was associated with a changed EMG signal, characterized by an increase in the early parts of the response (up to 225 ms) and a subsequent decrease. EMG onset latency was unaffected by training. This study is apparently one of the first to demonstrate that the response to sudden trunk loading can be improved in healthy subjects without an increase in pre-activation and associated trunk stiffness. In perspective, the results indicate a possibility for a training-induced reduction of the risk of low-back injuries, e.g., in nurses exposed to sudden trunk perturbations during patient handling.

Physical, psychosocial, and individual risk factors for neck/shoulder pain with pressure tenderness in the muscles among workers performing monotonous, repetitive work.

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To evaluate the effect of individual characteristics and physical and psychosocial workplace factors on neck/shoulder pain with pressure tenderness in the muscles. SUMMARY OF BACKGROUND DATA: Controversy prevails about the importance of workplace factors versus individual factors in the etiology of pain in the neck and/or shoulders. METHODS: Study participants were 3123 workers from 19 plants. Physical risk factors were evaluated via video observations, and psychosocial risk factors were assessed with the job content questionnaire. Other procedures included symptom survey, clinical examination, and assessment of health-related quality of life (SF-36). The main outcome variable, neck/shoulder pain with pressure tenderness, was defined on the basis of subjective pain score and pressure tenderness in muscles of the neck/shoulder region. RESULTS: The prevalence of neck/shoulder pain with pressure tenderness was 7.0% among participants performing repetitive work and 3.8% among the referents. We found an association with high repetitiveness (prevalence ratio 1.8, 95% confidence interval 1.1-2.9), high force (2.0, 1.2-3.3), and high repetitiveness and high force (2.3, 1.4-4.0). The strongest work-related psychosocial risk was high job demands (1.8, 1.2-2.7). Increased risk was also associated with neck/shoulder injury (2.6, 1.6-4.1), female gender (1.8, 1.2-2.8), and low pressure pain threshold (1.6, 1.1-2.3). Neck/shoulder pain was strongly associated with reduced health-related quality of life. CONCLUSIONS: Work-related physical and psychosocial factors, as well as several individual risk factors, are important in the understanding of neck/shoulder pain. The findings suggest that neck/shoulder pain has a multifactorial nature. Reduced health-related quality of life is associated with subjective pain and clinical signs from the neck and shoulders. The physical workplace factors were highly intercorrelated, and so the effect of individual physical exposures could only be disentangled to a minor degree.

Risk of shoulder tendinitis in relation to shoulder loads in monotonous repetitive work.

BACKGROUND: Few studies relate the occurrence of shoulder disorders to quantified ergonomic exposures. This study evaluates the hypothesis that shoulder loads in repetitive work might contribute to the occurrence of shoulder tendinitis. METHODS: This is a cross-sectional study of 1961 workers in repetitive work and 782 referents. Shoulder loads were quantified at task level and measures of exposures were assigned based on task distribution. Symptoms in combination with clinical criteria defined shoulder tendinitis. RESULTS: The prevalence of shoulder tendinitis was higher among exposed workers (adjusted OR 3.1, 95% CI 1.3-3). Neither frequency of movements (ranging 1-36/min) nor lack of micro-pauses in shoulder flexion (ranging 0-100% of cyclus time) was related to disease prevalence. Increasing force requirements (categorized as light = 1, somewhat hard = 2, hard = 3 or very hard = 4) increased risk slightly (OR 1.6, 95% CI 1.0-2.6 per unit). CONCLUSIONS: The results indicate that workers with repetitive tasks have increased risk of shoulder tendinitis, which partially can be attributed to force requirements.