David Rodrick

Biomechanical evaluation of nursing tasks in a hospital setting

A field study was conducted to investigate spinal kinematics and loading in the nursing profession using objective and subjective measurements of selected nursing tasks observed in a hospital setting. Spinal loading was estimated using trunk motion dynamics measured by the lumbar motion monitor (LMM) and lower back compressive and shear forces were estimated using the three-dimensional (3D) Static Strength Prediction Program. Subjective measures included the rate of perceived physical effort and the perceived risk of low back pain. A multiple logistic regression model, reported in the literature for predicting low back injury based on defined risk groups, was tested. The study results concluded that the major risk factors for low back injury in nurses were the weight of patients handled, trunk moment, and trunk axial rotation. The activities that required long time exposure to awkward postures were perceived by nurses as a high physical effort. This study also concluded that self-reported perceived exertion could be used as a tool to identify nursing activities with a high risk of low-back injury.

Is Chaos Present in Static Postures Observed at Work: A Nonlinear Dynamics-Based Analysis of Surface EMG Signals:

The primary objective of the study was to explore the nonlinear characteristics of surface electrical activity of the biceps muscle during two (job safety critical) static postures observed on the assembly line. The results showed that for each trial in both postures (posture 1: the MVC condition, and posture 2: the no-loading test posture) the positive Lyapunov exponents exist. However, the statistical test of significance showed that surface EMG of the biceps brachii was more chaotic under the maximum loading in simulated posture 1 than under the no-loading condition in simulated posture 2. At the same time it was observed that the recorded two types of time series (EMG data) were almost equally complex, indicating the same source of the data. The existence of chaos in the EMG measure of muscle activity may indicate that conventional analysis could bear little meaning in explaining muscular fatigue.

Nonlinear behavior of the center of pressure in simulated standing on elevated construction beams.

This study investigated the effects of width of construction beams and single-hand load holding task conditions on nonlinear behavior of the foot center of pressure (COP) exerted on the beam. The foot COP, defined as the point of application of the result of vertical forces acting on the surface of foot support, was measured in the lateral direction under simulated standing task conditions. Twelve healthy male subjects were asked to hold a load of 6.8 kg and 11.3 kg while standing on the elevated construction beams with widths of 10 and 22.5 cm (4 and 9 inches, respectively) under low and high foot separation (foot step). The results showed that both beam width and single-hand load carrying conditions had significant effects on the observed nonlinearity of the foot center of pressure exerted on the beam. Standing on the narrow beam resulted in higher level of chaotic behavior of COP compared to the wide beam condition. The nonlinearity of the COP exerted by the forward (left) foot was higher for the narrow beam condition. For both beams, the nonlinearity of the COP exerted by the forward (left) foot was consistently higher than the COP exerted by the backward (right) foot. Furthermore, for both beams, single-handed holding of the 11.3 kg load resulted in higher levels of COP nonlinearity than carrying 6.8 kg or no load at all. The study results indicate that nonlinear dynamics behavior of the forward foot under single-handed high load holding condition may be critical to preserving lateral stability during standing at the construction beams.

Nonlinear Behavior of Muscle Responses for Four Static Postures Observed at Work

The primary objective of the study was to explore the nonlinear characteristics of surface myoelectrical activity of the biceps muscle during four static postures observed on the assembly line. The results showed significant differences in the largest Lyapunov exponents between four postures. The surface EMG of the biceps brachii was more chaotic under the maximum loading in MVC posture with elbow fully extended (180 degrees) and static posture with 180 degrees shoulder flexion compared to two other static postures. Based on the Kaplan-Yorke dimension, it was found that dimensional complexity was higher for MVC posture than for posture with 135 degrees shoulder flexion, posture with 180 degrees shoulder flexion, and posture with 90 degrees shoulder flexion and abduction. Interaction effects of posture and trial with respect to the largest Lyapunov exponents and Kaplan-Yorke dimension characteristics of the EMG signals showed higher levels of chaos and complexity patterns in MVC postures compared to other static postures.