Shoulder muscular activity in individuals with low back pain and spinal cord injury during seated manual load transfer tasks.

This study aimed to compare the activity of four shoulder muscles in individuals with low back pain (LBP), spinal cord injuries (SCI) and a control group, during one-handed load transfer trials. Nine individuals with minimum one-year of LBP, eleven with thoracic/lumbar SCI and nine healthy controls participated in this study. The activations of anterior deltoid, upper trapezius, infraspinatus and pectoralis major were recorded by surface EMG during one-handed transferring of a cylinder from a home shelve to six spatially distributed target shelves.

The effect of bracing availability on one-hand isometric force exertion capability.

Unlabelled: Environmental obstructions that workers encounter can kinematically limit the postures that they can achieve. However, such obstructions can also provide an opportunity for additional support by bracing with the hand, thigh or other body part. The reaction forces on bracing surfaces, which are in addition to those acting at the feet and task hand, are hypothesised to improve force exertion capability, and become required inputs to biomechanical analysis of tasks with bracing.

A study of the difference between nominal and actual hand forces in two-handed sagittal plane whole-body exertions.

Given a task posture, changes in hand force magnitude and direction with regard to joint locations result in variations in joint loads. Previous work has quantified considerable vertical force components during push/pull exertions. The objective of this work was to quantify and statistically model actual hand forces in two-hand, standing exertions relative to the required nominal horizontal and vertical hand forces for a population of widely varying stature and strength.

The development of a model to predict the effects of worker and task factors on foot placements in manual material handling tasks.

Accurate prediction of foot placements in relation to hand locations during manual materials handling tasks is critical for prospective biomechanical analysis. To address this need, the effects of lifting task conditions and anthropometric variables on foot placements were studied in a laboratory experiment. In total, 20 men and women performed two-handed object transfers that required them to walk to a shelf, lift an object from the shelf at waist height and carry the object to a variety of locations.

The effects of insertion method and force on hand clearance envelopes for rubber hose insertion tasks.

Objective: The aim of this study was to determine how hand space for manual insertion of flexible hoses is affected by insertion method and force.

Background: Adequate space is needed during assembly tasks in which workers join parts together with their hands. Hose installations are an example of such a task.

The evolving role of biomechanics in prevention of overexertion injuries.

This paper describes occupational biomechanics as an evolving body of knowledge that has required not only a sophisticated development of fundamental biomechanical principles and human failure data, but also has required epidemiological information to enable a more complete understanding of how certain types of musculoskeletal injuries can be caused by specific physical work requirements. It also is argued that even with adequate biomechanical and epidemiological information, the ability to change working conditions and manual task requirements in companies required management and workers to become organised into formal ergonomics teams that could be trained and empowered to reduce the known biomechanical risk factors present in various jobs. It is demonstrated that in the last 35 years occupational biomechanics research continues to provide the intellectual machine that is driving the development of important ergonomics guidelines.

Wrist strength is dependent on simultaneous power grip intensity.

The effect of grip activities on wrist flexion/extension strength was examined. Twelve healthy subjects performed maximum wrist flexion/extension exertions with one of five levels of simultaneous grip effort: minimum effort; preferred effort; 30%, 60% and 100% maximum voluntary contraction. As grip force increased from the minimum to the maximum effort, average wrist flexion strength increased 34% and average wrist extension strength decreased 10%.

The effect of handle friction and inward or outward torque on maximum axial push force.

Objective: To investigate the relationship among friction, applied torque, and axial push force on cylindrical handles.

Background: We have earlier demonstrated that participants can exert greater contact force and torque in an "inward" movement of the hand about the long axis of a gripped cylinder (wrist flexion/forearm supination) than they can in an "outward" hand movement.

Method: Twelve healthy participants exerted anteriorly directed maximum push forces along the long axis of aluminum and rubber handles while applying deliberate inward or outward torques, no torque (straight), and an unspecified (preferred) torque.

Experimental evaluation of a computational shoulder musculoskeletal model.

Background: Many evaluations of shoulder biomechanical models have focused on static exertions in constrained postures, but few have considered tasks that are more complex. This study examines model performance in load delivery tasks for a range of target locations.

Methods: The study evaluated an optimization-based muscle force prediction model used to assess dynamic load transfer tasks.

Inward torque and high-friction handles can reduce required muscle efforts for torque generation.

Objective: The effects of handle friction and torque direction on muscle activity and torque are empirically investigated using cylindrical handles.

Background: A torque biomechanical model that considers contact force, friction, and torque direction was evaluated using different friction handles.

Methods: Twelve adults exerted hand torque in opposite directions about the long axis of a cylinder covered with aluminum or rubber while grip force, torque, and finger flexor electromyography (EMG) were recorded.

A mathematical musculoskeletal shoulder model for proactive ergonomic analysis.

Occupational shoulder musculoskeletal injuries and disorders are common. Generally available shoulder work analysis tools do not offer insight into specific muscle load magnitudes that may indicate increased risk, nor do they address many concerns germane to job analysis. To address these issues, a biomechanical model of the shoulder was developed to include several critical components: the systematic inclusion of kinematic and kinetic effects, population scalability, geometric realism, an empirical glenohumeral constraint, and integration with digital ergonomics analysis software tools.

The effect of torque direction and cylindrical handle diameter on the coupling between the hand and a cylindrical handle.

Pheasant and O'Neill's torque model (1975) was modified to account for grip force distributions. The modified model suggests that skin friction produced by twisting an object in the direction of fingertips causes flexion of the distal phalanges and increases grip force and, thus, torque. Twelve subjects grasped a cylindrical object with diameters of 45.

Kinematics of heelstrike during walking and carrying: implications for slip resistance testing.

Slip resistance measurements of shoes and floors are used to evaluate the potential for slip and fall injuries. These measurements are believed to have increased validity when they more closely reflect actual heelstrike biomechanics during locomotion. The purpose of this study was to describe heelstrike kinematics during load carrying to provide data towards improved slip resistance testing.

The relationship between shoulder torques and the perception of muscular effort in loaded reaches.

The objective of this study was to define the quantitative relationship between external dynamic shoulder torques and calibrated perceived muscular effort levels for load delivery tasks, for application in job analyses. Subjects performed a series of loaded reaches and, following each exertion, rated their perceived shoulder muscular effort. Motion and task physical requirements data were processed with a biomechanical upper extremity model to calculate external dynamic shoulder torques.

A computer algorithm for representing spatial-temporal structure of human motion and a motion generalization method.

Inspired by the generalized motor program (GMP) theory, this study presents a symbolic motion structure representation (SMSR) algorithm that identifies a basic spatial-temporal structure of a human motion. The algorithm resolves each joint angle-time trajectory of a multi-joint motion into a sequence of elemental motion segments and labels each motion segment with a symbol representing its shape ("U": monotonically increasing; "D": monotonically decreasing; "S": stationary). By concatenating symbols according to their order in time, the spatial-temporal structure of a joint angle-time trajectory is represented as a symbolic string.

Primary prevention of low back pain through the application of biomechanics in manual materials handling tasks.

Biomechanical models of the torso have become quite sophisticated in recent years. This paper describes how injurious stresses on the low back can be predicted by such models during the early phases of designing materials handling tasks in industry. It is shown that these biomechanical models can be used to simulate novel materials handling tasks, and thus be used to guide the design of such tasks to reduce various low back stresses.

Representing and identifying alternative movement techniques for goal-directed manual tasks.

Differences in motion patterns subserving the same movement goal can be identified qualitatively. These alternatives, which may characterize 'movement techniques' (e.g.