Biomedical subjects

Terry G Richard

Publications and source records attributed to Terry G Richard.

4 recordsLinked to original sources

PubMed2004

Upper limb mechanical changes following short duration repetitive eccentric exertions.

BACKGROUND: Power hand tool use is considered a risk factor for upper extremity musculoskeletal disorders. It is unclear if submaximal eccentric activity inherent to power tool use adversely affects the mechanical properties of muscle. METHODS: This study investigated in vivo changes in human upper limb dynamic mechanical properties following exposure to short-term repetitive submaximal eccentric exertions that are similar to operating an industrial power hand tool. Eighteen subjects (12 males and 6 females) were assigned to one of three exercise groups (isometric, eccentric or control) and exercised 10 min for 60 repetitions at 50% of isometric forearm supination maximum voluntary contraction. Supination strength and dynamic mechanical properties (stiffness, effective mass, and damping) of forearm rotation, modeled as a single-degree-of-freedom system during maximal exertion, were ascertained prior to exercise, immediately following exercise and 24 h later. FINDINGS: Strength decreased for the isometric (17%) (P < 0.05) and eccentric (34%) (P < 0.01) groups following exercise. Only the eccentric exercise group had a reduction in mechanical stiffness (53%) (P < 0.01) and effective mass (58%) (P < 0.05). The other groups had no changes in mechanical properties. INTERPRETATION: The change in mechanical properties following repetitive submaximal eccentric activity could negatively impact the ability of the arm to react to rapid forceful loading during repetitive industrial work activities and may indicate mechanical strain on the upper limb.

Adaptation, Physiological↗

PubMed2003

Forces associated with pneumatic power screwdriver operation: statics and dynamics.

The statics and dynamics of pneumatic power screwdriver operation were investigated in the context of predicting forces acting against the human operator. A static force model is described in the paper, based on tool geometry, mass, orientation in space, feed force, torque build up, and stall torque. Three common power hand tool shapes are considered, including pistol grip, right angle, and in-line. The static model estimates handle force needed to support a power nutrunner when it acts against the tightened fastener with a constant torque. A system of equations for static force and moment equilibrium conditions are established, and the resultant handle force (resolved in orthogonal directions) is calculated in matrix form. A dynamic model is formulated to describe pneumatic motor torque build-up characteristics dependent on threaded fastener joint hardness. Six pneumatic tools were tested to validate the deterministic model. The average torque prediction error was 6.6% (SD = 5.4%) and the average handle force prediction error was 6.7% (SD = 6.4%) for a medium-soft threaded fastener joint. The average torque prediction error was 5.2% (SD = 5.3%) and the average handle force prediction error was 3.6% (SD = 3.2%) for a hard threaded fastener joint. Use of these equations for estimating handle forces based on passive mechanical elements representing the human operator is also described. These models together should be useful for considering tool handle force in the selection and design of power screwdrivers, particularly for minimizing handle forces in the prevention of injuries and work related musculoskeletal disorders.

Biomechanical Phenomena↗

PubMed2003

A single-degree-of-freedom dynamic model predicts the range of human responses to impulsive forces produced by power hand tools.

The human operator is modelled as a single-degree-of-freedom dynamic mechanical system for predicting the response to impulsive torque reaction forces produced by rotating spindle power hand tools such as nutrunners or screwdrivers. The model uses mass, spring and damping elements to represent the standing operator supporting the tool in the hand. It was hypothesized that these mechanical elements are affected by work location and vary among individuals. These elements were ascertained by measuring the resulting frequency and amplitude of a freely oscillating defined mechanical system when externally loaded using maximal effort to oppose its motion. Twenty-five subjects (13 female, 12 male) participated in the full factorial experiment that measured the effects of gender, vertical and horizontal work location for various tool shapes (in-line, pistol, right angle), and orientations (horizontal and vertical). The mean operator stiffness decreased from 1721 to 1195 N/m when the horizontal work location increased from 30 to 90 cm in front of the ankles for a pistol-grip handle used on a vertical surface. Males had greater mass moment of inertia of (0.0099 kg m2) than females (0.0072 kg m2) for an in-line handle used on a horizontal surface. Internal validation by independently measuring apparatus torque found that the model satisfactorily explained the measured operator dynamics with an average error of 2.86%. Group variance reflects the range of operator capacities to react against power hand tool generated forces for the sample group and therefore it may also be useful for understanding the range of capacities among a group of operators performing similar tasks.

Adult↗

PubMedDate not supplied

Handle dynamics predictions for selected power hand tool applications.

This study uses a previously developed single-degree-of-freedom mechanical model to predict the power hand tool operator handle kinematic response to impulsive reaction forces (Lin, 2001). The model considers the human operator as a lumped parameter passive mechanical system, consisting of stiffness, mass moment of inertia, and viscous damping elements. Six power nutrunners were operated by 9 volunteers (3 men, 6 women) in the laboratory, and corresponding handle kinematics were compared against model predictions. A full-factorial experiment considered torque buildup time and work location. Normalized forearm flexor EMG was measured to quantify muscle exertions and used to proportionally adjust the stiffness parameter. The measured handle displacement for actual tool operation strongly correlated to the model predictions (R = .98) for all handle configurations. The overall model prediction error was 3% for predicting tool handle responses to impulsive reaction forces for various tool and workstation parameters. This model should make it possible for designers to identify conditions that minimize the torque reaction experienced by power hand tool operators.

Arm↗