Biomechanical, psychosocial and individual risk factors predicting low back functional impairment among furniture distribution employees.

BACKGROUND: Biomechanical, psychosocial and individual risk factors for low back disorder have been studied extensively however few researchers have examined all three risk factors. The objective of this was to develop a low back disorder risk model in furniture distribution workers using biomechanical, psychosocial and individual risk factors. METHODS: This was a prospective study with a six month follow-up time. There were 454 subjects at 9 furniture distribution facilities enrolled in the study. Biomechanical exposure was evaluated using the American Conference of Governmental Industrial Hygienists (2001) lifting threshold limit values for low back injury risk. Psychosocial and individual risk factors were evaluated via questionnaires. Low back health functional status was measured using the lumbar motion monitor. Low back disorder cases were defined as a loss of low back functional performance of -0.14 or more. FINDINGS: There were 92 cases of meaningful loss in low back functional performance and 185 non cases. A multivariate logistic regression model included baseline functional performance probability, facility, perceived workload, intermediated reach distance number of exertions above threshold limit values, job tenure manual material handling, and age combined to provide a model sensitivity of 68.5% and specificity of 71.9%. INTERPRETATION: The results of this study indicate which biomechanical, individual and psychosocial risk factors are important as well as how much of each risk factor is too much resulting in increased risk of low back disorder among furniture distribution workers.

Quantification of a meaningful change in low back functional impairment.

STUDY DESIGN: Repeated measures study design. OBJECTIVE: Determine a meaningful change in low back functional impairment as measured with the lumbar motion monitor. SUMMARY OF BACKGROUND DATA: A quantitative functional performance probability (P(n)) measure has been developed and is scored from 0.00 to 1.00. Previous research has shown that a 0.5 cut-off provides excellent sensitivity and specificity for identifying impaired and healthy low back function. However, a meaningful change in the P(n) measure has not been defined. METHODS: The lumbar motion monitor was used to repeatedly measure P(n) in 3 groups of subjects including (1) asymptomatic, (2) recovering low back pain (LBP) and, (3) nonrecovering LBP. The asymptomatic group had 20 subjects. The recovering and nonrecovering LBP had 18 and 8 subjects, respectively. The asymptomatic group was tested 5 times at 1-week intervals. The 2 LBP groups were tested every 2 weeks for 3 months (6 evaluations). RESULTS: The P(n) in the asymptomatic group did not significantly change over the observed period. On the basis of the variability in the asymptomatic group it was hypothesized that a meaningful change in P(n) was 0.14. The defined meaningful change was evaluated in 2 patient with LBP populations. The P(n) in the recovered LBP group significantly improved during the 3 month observation period and there was a corresponding reduction of symptoms. In the recovering LBP group the within subject standard deviation was 0.14 and all patients had at least 1 visit to visit change greater than 0.14. Furthermore, 11 of the 18 recovering patients with LBP had a meaningful change between the first 2 visits. In contrast, none of the nonrecovering LBP group had a meaningful change between the first 2 visits. CONCLUSION: A meaningful change in P(n) was defined as 0.14.

The effect of phone design on upper extremity discomfort and muscle fatigue.

OBJECTIVE: To compare a small cellular clamshell phone with a traditional office phone in the development of discomfort and muscle fatigue over time during phone use. BACKGROUND: Phone use involves low-level static exertions that may be influenced by phone design. Phone design and its interactions with anthropometry may change shoulder and hand postures assumed during use, which in turn may modify the length-strength relationship and moment arms of the muscles. METHOD: Ten adults participated in a study that simulated phone use using a small clamshell and a traditional office phone. Discomfort information and electromyographic (EMG) muscle activity were monitored on four upper extremity muscles. Discomfort and fatigue data (EMG median frequency shifts) were analyzed to assess differences between phones as well as differing effects attributable to anthropometry. RESULTS: Median frequency shifts supported discomfort claims and indicated muscle fatigue in the deltoid and thenar muscles. Biomechanical measures demonstrated that participants with short limb lengths developed more severe signs of thenar fatigue. Participants with longer arms developed greater discomfort in the neck, shoulder, and back. The deltoid confirmed this occurrence, showing signs of muscle fatigue. CONCLUSION: Phone design and anthropometry influenced the development of discomfort and fatigue during phone use. Phone design dictated grip style, resulting in differing discomfort and fatigue levels. Anthropometry influenced the severity of the discomfort and fatigue present in the shoulder and hand. APPLICATION: Use of small clamshell phones may contribute to a lack of rest and recovery from typical workday exposures. It should be explored from an ergonomic perspective.

Changes in spine loading patterns throughout the workday as a function of experience, lift frequency, and personality.

BACKGROUND CONTEXT: Psychosocial stressors have been associated with low back pain reporting. However, response to psychosocial risk factors may be dependent on the individual's personality type that, in turn, can affect muscle recruitment and spine loading. This study explores how personality might be associated with spine loading during repetitive lifting performed throughout an entire work shift. PURPOSE: Assess spine loading as a function of an individual's personality type during repetitive, long-term exposure to a materials handling tasks. STUDY DESIGN: Laboratory experiment where experienced and inexperienced participants performed repetitive, asymmetric lifts at various load and lift frequency levels throughout a series of 8-hour exposure periods. Spine loads were monitored throughout the work period. PATIENT SAMPLE: Twelve novice and 12 experienced materials handlers who were asymptomatic for back pain. OUTCOME MEASURES: Spine compression, anterior-posterior (A/P) shear, and lateral shear at the L5-S1 level. METHODS: Participants were categorized into personality types based upon the Myers-Briggs personality type indicator. An electromyography-assisted biomechanical model was used to assess spine compression, A/P shear, and lateral shear throughout the exposure period. RESULTS: The results indicate that intuitors had higher shear spinal loading regardless of moment exposure, lift frequency, and time through the work period, compared with the sensor personality type. In addition, higher spine compressive and shear forces occurred in the perceiver personality compared with the judgers' personality trait, regardless of moment and, often, lift frequency. Novice lifters typically experienced greater spine loading. CONCLUSIONS: The results suggest that when there exists a personality-job environment mismatch, spinal loading increases via an increase in antagonistic co-contraction. The trends suggest that inherent personality characteristics may play a role in one's motor control strategies when performing a repetitive lifting task.

Differences among outcome measures in occupational low back pain.

The rate of recurrence in low back pain patients has been reported as high as 70%; therefore, it is believed that researchers have a poor understanding of low back pain recovery. To enhance our understanding of recovery, a large cross-sectional study was conducted to compare outcome measures of return to work, impairment of activities of daily living, pain symptoms, and functional performance probability. A total of 208 workers were examined. The percentage of workers recovered based on return to work criteria was 99% compared to 25% for impairment of activities of daily living, 17% for symptoms, and 12.5% for functional performance probability. Single functional performance measures of range of motion, velocity, and acceleration had recovery rates of 59, 13, and 10%, respectively. It appears that all these criteria are measuring very different parameters of low back pain recovery. The residual loss in functional performance may indicate a decreased tolerance to physical demand providing potential insight for why recurrent low back pain rates are high.

Differences in motor recruitment and resulting kinematics between low back pain patients and asymptomatic participants during lifting exertions.

BACKGROUND: Low back disorders are a prevalent problem in society today and may lead to chronic debilitating low back pain. Developing our understanding of temporal muscle and kinematic patterns during manual material handling tasks may provide insight for preventing the cascading series of events leading to chronic low back pain. METHODS: Sixty-two low back pain patients and 61 asymptomatic participants performed a variety of lifting exertions that varied in lift origin horizontal and vertical distance, lift asymmetry, and weight. Electromyographic activity of 10 trunk muscles as well as trunk and pelvic kinematics was recorded during each exertion. Differences in muscle activation and kinematic parameters were compared between low back pain patients and asymptomatic participants as a function of experimental conditions. FINDINGS: Both the left and right erector spinae activated significantly earlier and were on significantly longer in low back pain patients compared to asymptomatic participants. The horizontal and vertical location of the lift influenced the EMG and kinematic differences between the low back pain patients and asymptomatic participants. INTERPRETATION: These finding indicate that low back pain patients would be exposed to increase muscle activity resulting in higher spine loads for a greater length of time compared to asymptomatic participants. The longer exposure time to increased spine load may lead to greater risk of future low back injury and cascading events leading to debilitating low back pain. The longer muscle activation time suggests that low back pain patients have changed their motor program from an open to a closed loop system.

The influence of individual low back health status on workplace trunk kinematics and risk of low back disorder.

A case-control study was conducted to determine whether or not kinematic-based low back disorder risk measurement (Marras et al. 1993) of the job was significantly different for those workers suffering from recent low back injuries compared to asymptomatic controls. Two hundred low back injured workers returning to full duty work and 200 asymptomatic controls were evaluated while performing the same job. There were no statistically significant differences between the two groups on any trunk motion measures or workplace measures. Therefore, job design is dictating the kinematic motions of the torso and not the worker's low back health. In addition, there was not a significant difference in job risk estimates using the lumbar motion monitor risk model. The mean risk (and standard deviation) for the low back injured group and the asymptomatic controls was 0.502 (0.178) and 0.501 (0.193), respectively. This study suggests that trunk kinematics and subsequent risk estimates are dictated primarily by job design and not influenced by the low back health status of the worker.