Effectiveness of job rotation for preventing work-related musculoskeletal diseases: a cluster randomised controlled trial.

OBJECTIVE: Job rotation is an organisational strategy widely used on assembly lines in manufacturing industries to mitigate workers' exposure so as to prevent musculoskeletal disorders. This study aimed to evaluate the effectiveness of job rotation for reducing working hours lost due to sick leave resulting from musculoskeletal diseases. METHODS: The design consisted of a 1-year cluster randomised controlled trial with a blinded assessor. Production sectors of the textile industry were randomised to intervention and control groups. Both groups received ergonomic training. The intervention group performed a job rotation programme. The primary outcome measure was number of working hours lost due to sick leave as a result of musculoskeletal disease (ICD-10). The secondary outcome measures were musculoskeletal symptoms (Yes/No), risk factors for musculoskeletal diseases (0-10), psychosocial factors and fatigue (0-100), general health (0-100), and productivity (0-10). All secondary outcomes were measured at baseline and 12-month follow-up. RESULTS: At the 12-month follow-up, both groups showed an increase in the number of working hours lost due to sick leave for musculoskeletal disease. There was no significant difference between the job rotation intervention group (mean deviation -5.6 hours, 95% CI -25.0 to 13.8) at the 12-month follow-up and the control group. There were no significant differences between groups for the secondary outcomes (p>0.05). CONCLUSIONS: The job rotation programme was not effective in reducing the number of working hours lost due to sick leave, decreasing the prevalence of musculoskeletal symptoms, or improving perception of musculoskeletal pain and workplace risk factors, psychosocial risk factors and productivity. TRIAL REGISTRATION NUMBER: NCT01979731.

Occupational injuries for consecutive and cumulative shifts among hospital registered nurses and patient care associates: a case-control study.

Nontraditional work shifts for hospital registered nurses and patient care associates and associated injuries were examined through a case-control study. Inpatient care requires that many staff work nontraditional shifts, including nights and 12-hour shifts, but some characteristics remain unexplored, especially consecutive shifts. A total of 502 cases (injured workers) were matched to single controls based on their hospital, unit type, job type, gender, and age (± 5 years). Conditional logistic regression was used for the analysis, controlling for weekly hours scheduled. For both, consecutive shifts of 2 or more days and some various cumulative shifts over a week and month period, especially night shifts, were associated with increased odds of injury. More investigations on the phenomenon of consecutive shifts are recommended. Additionally, the assessment of shift policy and subsequent injury outcomes is necessary before implementing intervention strategies.

Musculoskeletal disorders and ergonomic hazards among Iranian physicians.

BACKGROUND: The aim of this study was to determine the prevalence of musculoskeletal disorders (MSDs) and ergonomic hazards and their relationship among Iranian physicians who work in teaching hospitals. METHODS: A self-administered questionnaire was provided to 405 physicians in four teaching hospitals. The questionnaire had three major parts: the first part gathered individual and work-related data, the second was a modified version of the Standardized Nordic questionnaire for musculoskeletal symptoms, and the last part evaluated the duration of exposure to ergonomic hazards at work. RESULTS: Knee pain (19.8%) was the most common complaint among physicians, followed by low back (15.1%) and neck pain (9.8%). A total of 169 physicians (41.7%) reported symptoms in at least one part of their bodies. Prolonged sitting, standing, and neck flexion were the most common reported ergonomic hazards among participants. Multiple logistic regression analysis reported statistically significant associations for the outcomes of knee pain and symptoms in any part of the body with the work-related factors of years of employment and work hours per shift. CONCLUSION: The prevalence of musculoskeletal complaints among physicians was low, less than other health care workers, but similar to those reported in the general population. These musculoskeletal complaints were, however, associated with traditional work-related and ergonomic factors.

Daily computer usage correlated with undergraduate students' musculoskeletal symptoms.

BACKGROUND: A pilot prospective study was performed to examine the relationships between daily computer usage time and musculoskeletal symptoms on undergraduate students. METHODS: For three separate 1-week study periods distributed over a semester, 27 students reported body part-specific musculoskeletal symptoms three to five times daily. Daily computer usage time for the 24-hr period preceding each symptom report was calculated from computer input device activities measured directly by software loaded on each participant's primary computer. General Estimating Equation models tested the relationships between daily computer usage and symptom reporting. RESULTS: Daily computer usage longer than 3 hr was significantly associated with an odds ratio 1.50 (1.01-2.25) of reporting symptoms. Odds of reporting symptoms also increased with quartiles of daily exposure. CONCLUSIONS: These data suggest a potential dose-response relationship between daily computer usage time and musculoskeletal symptoms.

Seat inclination, use of lumbar support and low-back pain of taxi drivers.

OBJECTIVES: Epidemiologic evidence supporting optimal seating is limited and inconsistent. This cross-sectional study was conducted to examine the association between seat inclination, use of lumbar support, and the prevalence of clinically significant low-back pain among taxi drivers METHODS: A digital inclinometer was used to measure inclinations of seat surfaces (theta(seat)) and backrests (theta(back)), and calculate the back-to-thigh angle (theta(back-thigh)). Structured interviews were conducted to gather information on the use of lumbar support and the prevalence of low-back pain that had led to medical attention or absence from driving in the past month. A multiple logistic regression analysis was used to estimate the prevalence odds ratio (OR) with adjustment for age, body mass index, professional seniority, monthly driving hours, and the intensity of exposure to whole-body vibration. RESULTS: Among 224 drivers, the mean theta(seat), and theta(backrest) were 14.5 (SD 9.6) and 95.1 (SD 2.7) degrees, respectively, resulting in theta(back-thigh) of 80.6 (SD 9.3) degrees. Fifty-five percent used a lumbar support regularly, but 25% reportedly had significant low-back pain. The prevalence of low-back pain was 23% among those with theta(back-thigh) <86 degrees, 37% for those with a theta(back-thigh) of 86 approximately 91 degrees, and 9% for a theta(back-thigh) of >91 degrees. The adjusted OR comparing those with a theta(back-thigh) of < or = 91 degrees to those with a theta(back-thigh) of >91 degrees was 5.11 [95% confidence interval (95% CI) 1.07 approximately 24.4]. For regularly using drivers versus those not using lumbar support, the prevalence of low-back pain was 18% versus 34%, with an adjusted OR of 0.33 (95% CI 0.16 approximately 0.68). Neither theta(seat) nor theta(backrest) alone was significantly associated with low-back pain. CONCLUSIONS: The epidemiologic observation of this study was consistent with the results of prior biomechanical studies on appropriate seat inclinations and the use of lumbar support. Prospective studies are needed to confirm the true beneficial effects of these seating parameters.

Finger flexor tendon forces are a complex function of finger joint motions and fingertip forces.

In vivo tendon forces provide a view inside the musculoskeletal system revealing muscle function and potential injury etiologies. The studies presented here measured the in vivo tendon force of the flexor digitorum superficialis of the long finger during open carpal tunnel release surgery in ten adult patients. Forces were measured during passive movement of the finger, isometric pinch, and dynamic tapping of the finger. The tendon forces during passive movement of the finger were the largest with the finger fully extended. During isometric pinch, tendon force was linearly related to fingertip force, and was on average 3.3 times larger than the fingertip force. During dynamic activities, however, the relationship between tip and tendon force was nonlinear and often remained elevated when the finger was moving but with no applied force. Tendon forces were the highest with the isometric finger pinch. In conclusion, tendon force is a completed function of both fingertip load and motion of the joints that the tendons cross. A comparison of these results with others published in the literature indicated that rehabilitation processes need to incorporate a systems approach rather than rely on one specific physiologic relationship to minimize finger flexor tendon forces.

Fatigue in the forearm resulting from low-level repetitive ulnar deviation.

This study measured low-frequency fatigue (LFF) in the extensor carpi ulnaris (ECU) muscle while workers completed a repetitive ulnar deviation task. Using a repeated measures design, 10 healthy women participated in three conditions, each lasting 2 consecutive days: a control condition in which subjects remained inactive, and two repetitive work conditions involving repeated ulnar deviation of the wrist at 20 and 25 repetitions per minute at individual workloads deemed acceptable for 8 hours through a psychophysical protocol. LFF of the ECU muscle and self-reported levels of fatigue were recorded eight times throughout the control and workdays before (time 0), during (2, 4.25, 6.75, 8 hours), and after (9, 10, and 11 hours) exposure. The ratio of the isometric force produced by electrical stimulus at 20 pulses per second (pps) to the isometric force produced by 50 pps provided the measure of LFF. The ratios were lower on workdays compared with the control days, indicating the presence of LFF during repetitive work. During repetitive work the ratios decreased during the day, indicating the muscles fatigued as the day progressed. The psychophysically determined workloads, although not creating noticeable discomfort to the subjects, were high enough to create low levels of muscle fatigue.

Non-linear viscoelastic models predict fingertip pulp force-displacement characteristics during voluntary tapping.

We evaluated whether lumped-parameter non-linear viscoelastic models of human fingertip tissue can describe fingertip force-displacement characteristics during a range of rapid, dynamic tapping tasks. Eight human subjects tapped with their index finger on the surface of a rigid load cell while an optical system tracked fingertip position using an infra-red LED attached to the fingernail. Four different tapping conditions were tested: normal and high-speed taps with a relaxed hand, and normal and high-speed taps with the other fingers co-contracted. A non-linear viscoelastic model comprised of an instantaneous stiffness function and viscous relaxation function was capable of predicting fingertip tissue force response due to measured pulp compression under these four different loading conditions. The model could successfully reconstruct very rapid (less than 5 ms) force transients, and forces occurring over time periods greater than 100 ms, with errors of 10%. Model parameters varied by less than 20% over the four conditions, despite almost 3-fold differences in average forces and 38% differences in fingertip velocities. Energy dissipation by the fingertip averaged 81%, and varied little (<3%) across conditions, despite a 1. 5-fold range of energy input. The ability of a lumped-parameter model to describe fingertip force-displacement characteristics during a range of conditions contributes both to understanding the transmission of force through the fingertip to the musculoskeletal system and to predicting the stimulation of mechano-receptors located within the fingertip.

Electromyographic activity of the human extensor carpi ulnaris muscle changes with exposure to repetitive ulnar deviation.

With little known about the changes in muscle physiology due to repetitive work during an 8 h workday, our objective was to quantify the changes in muscle activity due to this type of work. Using a repeated measurements design, 13 healthy women participated in three conditions, each lasting 2 days: a control condition where they remained inactive, and two repetitive work conditions involving repeated ulnar deviation of the wrist at 20 and 25 repetitions a minute at workloads which they themselves had deemed acceptable for 8 h through a psychophysical protocol. Electromyographic (EMG) activity of the extensor carpi ulnaris muscle was recorded during voluntary isometric contractions (20% and 60% maximal voluntary contraction) eight times throughout the work and control days at 0, 2, 4.25, 6.75, 8, 9, 10, and 11 h. The amplitude of the EMG signal was lower on workdays compared to the control days. Although power was significantly reduced in all spectrum bands of the EMG power spectra, the reductions were not uniform across the entire frequency range, giving rise to different shapes of the EMG power spectra. Initial median frequency of the EMG signal showed no change between the control and workdays (P = 0.51); however, the decline of the median frequency with respect to time over the course of each isometric contraction was steeper during workdays compared to control days (P = 0.003). These changes suggest that the muscles are in an early stage of fatigue when working for an 8 h day.

Occupational injuries among Boston bicycle messengers.

BACKGROUND: Urban bicycle couriers may have a high incidence of injuries. Most messengers work as contractors and hence their injuries are not well documented. METHODS: To quantify injury rates and severity among urban bicycle couriers a convenience sample of 113 couriers in the city of Boston completed a two-page self-administered survey. RESULTS: Most working couriers have suffered at least one injury resulting either in days lost from work (70%) and in visits to a health-care professional or hospital (55%). The annual incidence rate for injuries resulting in days away from work was 47/100-bike couriers. Bone fractures accounted for the most days lost from work, followed by dislocations, sprains, and strains. Collisions and avoiding collisions with motor vehicles, including being "doored," and collisions with pedestrians accounted for the majority (66%) of events leading to injury. Twenty-four percent of messengers reported wearing a helmet on a regular basis, and 32% have health insurance. CONCLUSIONS: Urban bicycle messengers are a poorly documented, largely unstudied workforce who suffer a very high rate of occupational injury.

Longer distal motor latency predicts better outcomes of carpal tunnel release.

The association of preoperative median nerve distal latencies with surgical outcomes of carpal tunnel release is unclear. A total of 109 surgically treated workers with carpal tunnel syndrome across the state of Maine completed questionnaires assessing preoperative levels of symptom and functional limitations and general physical health (SF-12). A second questionnaire assessed the 6-month postoperative outcomes of symptom severity, functional limitations, and satisfaction with surgery. Univariate analyses indicated that longer preoperative distal motor and sensory latencies were associated with less postoperative levels of symptom, less postoperative functional limitations, and more satisfaction with surgery. The associations persisted in multiple linear regression analysis; however, better general health preoperatively was a better predictor of favorable outcomes. The results suggest that workers with prolonged preoperative distal motor latencies and who are in good general health preoperatively have a higher rate of successful carpal tunnel release surgery.