Power grip strength as a function of tool handle orientation and location.

Thirty male volunteers participated in a study evaluating the effect of workspace envelope (work height and reach distance) and handle orientation on grip force capacity. Maximum voluntary power grip exertions were recorded using instrumented tool handles under three conditions: a pistol grip tool handle oriented horizontally and vertically and a right angle tool handle oriented horizontally. Significant main effects of handle height and reach location on normalized grip force capacity were observed with the horizontally oriented pistol grip and right angle handles, whereas only an interaction effect was observed with the vertically oriented pistol grip handle. Comparison of results to scores produced with a job assessment tool (RULA) is included as an appendix. The proposed methodology can provide information useful to job, workstation or tool design directed toward best accommodating the physical capacities of workers performing hand tool tasks.

Effects of user experience, working posture and joint hardness on powered nutrunner torque reactions.

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force and upper limb muscle activity (electromyography (EMG)) due to the effects of operator experience, working height and distance, type of tool and fastener joint hardness were measured in this study with 15 experienced and 15 novice nutrunner users. The results show that when pistol grip handles were used to work on a horizontal surface, experienced users allowed an average handle displacement of 7.9 degrees, while novice users allowed 11.5 degrees. Average EMG scaled by reference voluntary contraction (RVC) at forearm flexors, forearm extensors and biceps were greater for experienced users (318% RVC, 285% RVC, 143% RVC, respectively) than for novice users (246% RVC, 219% RVC, 113% RVC, respectively). Experienced users exerted more grip force than novice users when using right angle handles, but less force when using pistol grip handles. The results suggest that it is possible to minimize tool handle displacement by adapting the workplace layout to permit different working postures for each user group.

A system for the measurement of grip forces and applied moments during hand tool use.

Quantification of the forces applied with or by hand tools can be a difficult but important component of an ergonomic evaluation. This paper describes a device for measuring gripping forces and the moments generated by a hand tool. Laboratory characterization indicated that the device had good linearity (r2 = 0.999) with minimal hysteresis or creep. The working range exceeds 700N for gripping forces, and 28 and 16Nm for the two applied moment axes. The device, configured as a boning knife, was sensitive to differences in grip forces and applied moments in a simulated meat cutting task requiring distinct levels of precision. Significant individual variation in the "efficiency" of grip force was also observed. The system design is flexible, allowing for additional tool configurations.

Timing of activation of the erector spinae and hamstrings during a trunk flexion and extension task.

STUDY DESIGN: Timing of activation of the hamstrings and erector spinae was assessed using surface electromyography. OBJECTIVES: To investigate the influence of posture and movement speed during trunk flexion-extension on the flexion-relaxation response and trunk muscle activation patterns. SUMMARY OF BACKGROUND DATA: The literature contains numerous reports on coactivity and synergistic behavior of major muscle groups during trunk flexion-extension. There are few reports on the timing of muscle activation. METHODS: Six subjects were recruited for a training session and six biweekly test sessions. Ten surface electromyogram electrodes and a lordosimeter were used to record timing of lumbar motion and muscle recruitment in the hamstrings and at four sites in the thoracolumbar region. A 3 x 2 within-subject factorial design was used to test the effects of posture and speed on activation patterns. RESULTS: Patterns of muscle activation were found to be dependent on posture and the direction of movement. The flexion-relaxation response was pervasive in the lumbar region but was less consistent at the T9 and hamstring sites. Significant differences in the delay between electromyogram activation and lumbar motion were found for the standing postures at initiation of extension, in which activation progressed in the caudad-to-cephalad direction. CONCLUSIONS: The flexion-relaxation response is ubiquitous in the lumbar erector spinae and is present in the hamstrings and lower thoracic erector spinae, although not consistently in all subjects. In standing, timing of activation differed significantly by site in extension but not in flexion. Muscle activation patterns and flexion-relaxation were consistent over six biweekly test sessions.

A method for dynamic measurement of lumbar lordosis.

Trunk flexion-extension is accomplished with pelvic and thoracic rotation in the sagittal plane and a smooth coordination of lumbar vertebral translation and rotation. Several systems exist that measure gross trunk movements, but they typically do not track changes in lumbar arc length or curvature. A method for dynamic measurement of changes in lumbar arc length that uses a lordosimeter is presented. A static validation study of postures showed that the measurements are repeatable and compare favorably with a standard measure of lumbar curvature. In a dynamic validation study of a lifting task with a 23-kg load, the measurement method was highly correlated with thoracic and pelvic angular displacement. A discussion of the utility of this measure in biomechanical modeling is presented. A clinical or field version of the lordosimeter is also described.

The relation between pain intensity, disability, and the episodic nature of chronic and recurrent low back pain.

STUDY DESIGN: An observational study on the course of chronic and recurrent low back pain and its relation to disability and medication use performed on the basis of daily diary recording. OBJECTIVES: To provide a description of daily pain reporting by individuals with self-reported chronic and recurrent low back pain, to study how the intensity and episodic nature of low back pain is related to disability and medication use, and to classify subjects according to Von Korff's categories of chronic low back pain. SUMMARY OF BACKGROUND DATA: The natural history of low back pain has been described, and some classification schemes have been proposed, but little has been reported on pain characteristics and their relation to self-report of disability. METHODS: Daily self-reports of pain intensity, social and work disability, and medication use were collected from 94 participants with self-reported chronic or recurrent low back pain over a 6-month period. A metric for describing the episodic nature of chronic low back pain was developed. RESULTS: A significant effect of pain intensity on disability was found. During an episode, participants had significantly greater disability and medication use. Work-related disability and medication use was significantly greater in the latter half of an episode. CONCLUSIONS: Pain intensity can affect disability, but the episodic nature of low back pain also affects the ability to function in both work and personal life. Intermittent increases in pain can markedly alter disability. Chronic low back pain should not be treated as a static phenomenon.

Development of a set of equations describing joint trajectories during para-sagittal lifting.

Given a lifting task with predetermined starting and ending positions, the angular trajectories are usually very consistent with a distinctive pattern. This paper derives a set of equations that can describe the joint trajectories during a para-sagittal lifting task. Three optimal motion patterns were also expressed by the polynomials: minimal hand jerk, minimal center of gravity (CG) jerk, and minimal muscle utilization rate (MUR). The variability of the joint movements were synthesized by overlapping the optimal patterns.

The effect of industrial back belts and breathing technique on trunk and pelvic coordination during a lifting task.

STUDY DESIGN: Relative phase angle was used to study segmental motion patterns during a lifting and lowering task. OBJECTIVES: To investigate the effect of back belts, breathing technique, and their interaction on lumbar and pelvic motion patterns. SUMMARY OF BACKGROUND DATA: Trunk and pelvic coordination has been investigated in healthy and low back pain populations. Back belts have been shown to alter range of motion and intra-abdominal pressure. Little has been reported about belts and coordination during lifting and lowering. Phase angle has been used for quantifying segmental coordination. METHODS: Six individuals performed lifting/lowering tasks with a 23-kg load under elastic, rigid, and no belt conditions. During a second session, individuals were trained in Valsalva's maneuver and repeated the protocol. Cinematography was used to track trunk and pelvis displacements. RESULTS: Segmental coordination during lowering generally was found to be the inverse of lifting. Significant differences in the relation between lumbar and pelvis phase angles were found during the initial stage of lifting because of the interaction of belt use and breathing. Lumbar range of motion decreased significantly with belt use during lifting and lowering. No significant change in pelvis range of motion was observed. CONCLUSIONS: Back belt use and breathing technique interacted during the initial stage of lifting to significantly alter the lumbar and pelvis phase angles. The change in segmental kinematics was similar to that previously reported for patients with a history of low back pain. Lumbar range of motion significantly decreased with belt use during both lifting and lowering.

Maximum acceptable forces of dynamic pushing: comparison of two techniques.

The purpose of this experiment was to investigate maximum acceptable initial and sustained forces while performing a push of 7.6 m, performed at a frequency of 1 push min-1 on a magnetic particle brake treadmill and a high-inertia push-cart. Eight male industrial workers performed a 40 min treadmill pushing task in the context of a larger experiment and two, 2 h push-cart tasks with a unique water loading system. A psychophysical methodology was employed, whereby the subjects were asked to select a workload they could sustain for 8 h without straining themselves or without becoming unusually tired, weakened, overheated or out of breath. The results revealed that maximum acceptable initial and sustained forces of pushing on the high inertia cart were significantly higher (28 and 23%, respectively) than pushing forces on the magnetic particle brake treadmill. It was concluded that adjustments to the pushing and pulling data bank by Snook and Ciriello (1991) may be appropriate if verification of this experiment yields similar results.

The reduction of chronic nonspecific low back pain through the control of early morning lumbar flexion. A randomized controlled trial.

STUDY DESIGN: Eighteen-month, randomized controlled trial with partial crossover. OBJECTIVES: To test the hypothesis that the control of lumbar flexion in the early morning will significantly reduce chronic, nonspecific low back pain. SUMMARY OF BACKGROUND DATA: Previous studies have indicated an increased risk of low back pain with bending forward in the early morning, primarily because of increased fluid content in the intervertebral discs at that time. METHODS: After 6 months of recording baseline data, 85 subjects with persistent or recurring low back pain were randomly assigned to treatment and control groups. The treatment group received instruction in the control of early morning lumbar flexion. The control group received a sham treatment of six exercises shown to be ineffective in reducing low back pain. Six months later, the control group received the experimental treatment, Diaries were used to record daily levels of pain intensity, disability, impairment, and medication usage. RESULTS: Significant reductions in pain intensity (P < 0.01) were recorded for the treatment group, but not for the control group (point estimate, 33%; 95% confidence interval, 11-55%). After receiving the experimental treatment, the control group responded with similar reductions (P < 0.05). Significant reductions also were observed in total days in pain, disability, impairment, and medication usage. CONCLUSIONS: Controlling lumbar flexion in the early morning is a form of self-care with potential for reducing pain and costs associated with chronic, nonspecific low back pain.

Meteorological conditions and self-report of low back pain.

STUDY DESIGN: Six months of daily low back pain ratings for 94 individuals were tested for the influence of prevailing weather conditions during the spring, summer, and fall seasons. Intergroup differences were tested for study participants who reported weather sensitivity and for those who did not. OBJECTIVES: To investigate the relation between pain ratings and prevailing weather conditions in a population with chronic or recurrent low back pain. SUMMARY OF BACKGROUND DATA: Weather conditions have been reported to influence pain perception in some disease states, including low back pain. Investigations of this relation in chronic or recurrent low back pain have involved varied methodologies, and conflicting results have been reported. METHODS: The effects of eight weather variables reported to influence musculoskeletal pain were tested on daily pain ratings. A post hoc weather sensitivity questionnaire was used to disperse 73 individuals into groups based on perceived weather sensitivity, and group differences were tested. RESULTS: Significant effects on pain scores were found, most notably for temperature and vapor pressure. The magnitude of the effects were small compared with autocorrelation of an individual's own pain scores. Significant differences were found between the group of individuals who were insensitive to weather conditions and that of individuals with perceived sensitivity to cold temperatures. No significant intergroup differences were found for damp, rainy conditions or changes in barometric pressure. CONCLUSIONS: Weather conditions may influence subjective reporting of low back pain significantly. Although the effects are small in magnitude, they should be considered in clinical treatment of the patient with chronic, nonspecific low back pain. Pain scores may demonstrate greater interaction with certain weather conditions in individuals perceiving sensitivity to those conditions.

Three different lifting strategies for controlling the motion patterns of the external load.

Co-ordination of various components of the human body during the course of lifting are very complex and difficult to control. This study hypothesized that strategies used to control the motion patterns of the external load may be applied to control co-ordination and also to control the level of compressive force on the lumbosacral joint. A simulation of lifting based on the optimization approach was introduced to generate three classes of unique dynamic motion patterns of the external load directed by three different objective functions. The first objective function was to maximize the smoothness of the motion pattern of the external load. The second objective function was to minimize the sudden change of the centre of gravity of the body-load system. The third objective was to minimize the integration over time of the sum of the square of the ratio of the predicted joint moments to the corresponding joint strength during the course of lifting. Eight subjects were recruited to perform 40 lifts using each of the three optimal motion patterns of the load. Compressive forces on the lumbosacral joint were computed and compared. The data showed with statistical significance that subjects using the motion patterns of the external load suggested by the first objective function had the lowest compressive force peaks. Thus, this study satisfied two goals: (1) it indexed and synthesized three motion patterns of the external load by three biomechanically unique objective functions, and (2) it established the association between the spinal loading and the control of the motion patterns of the external load during lifting.