Biomedical subjects

Joan M Stevenson

Publications and source records attributed to Joan M Stevenson.

6 recordsLinked to original sources

PubMed2006

Principal component analysis of lifting waveforms.

BACKGROUND: One limiting factor in lifting research design has been the inability to effectively analyze waveform data, especially when differences in body mass, height, and load magnitude influence the derived kinetic variables. The purpose of this study was to demonstrate the sensitivity of principal component analysis to quantify clinically relevant differences in kinetic lifting waveforms over three load magnitudes and between two separate populations. METHODS: Principal component analysis was applied to five kinetic lifting waveforms. The derived principal component scores were used as the dependent measures in a two-way (clinical status x load magnitude) MANOVA. FINDINGS: Significant low back pain group differences (P<0.05) were found for three of the principal component scores on extension moment generation in the sacral and thoracic regions and for trunk compression. Significant differences were found for each variable with respect to the magnitude across the entire lift time between the three load conditions, as well as four significant differences related to inferred mechanical changes that resulted from lifting increasingly heavier loads. INTERPRETATION: Principal component analysis of kinetic lifting waveforms was shown to be insensitive to a confounding factor of different load magnitudes when attempting to identify previously determined clinically relevant differences in the waveform trajectories. The analysis was able to partition the variability attributed to the direct influence of different external load magnitudes, versus those differences in spinal loading that arose from the variations in the lifting mechanics of increasing loads. The technique could be beneficial for other kinetic analyses where confounding magnitude modifiers like body size are present.

Adult↗

PubMed2006

An on-body personal lift augmentation device (PLAD) reduces EMG amplitude of erector spinae during lifting tasks.

BACKGROUND: A new on-body personal lift augmentation device was developed to support the back muscles during the repetitive lifting task. METHODS: Nine male subjects participated in the study. Three Fastrak units were used to record positions and rotations of the segments. Trunk muscle normalized and integrated electromyography of the left and right thoracic erector spinae, lumbar erector spinae, external obliques, and rectus abdominis, as well as the kinematic variables of peak lumbar angle, peak pelvis angle, peak trunk acceleration, peak load acceleration were compared in symmetrical lifting for three different loads (5 kg, 15 kg, 25 kg) with three different styles (stooped, squat, free) under two conditions of with and without personal lift assist device. FINDINGS: The lift assist device significantly reduced the required muscular effort of the lumbar (p = 0.001) and thoracic erector spinae with no significant differences in the level of abdominal muscle activity. The amount of integrated electromyography reduction ranged from 14.4% to 27.6% for the lumbar and thoracic erector spinae respectively. Simple measures of trunk posture and accelerations confirmed that there were no differences in lifting technique that would cause the integrated electromyography activity to be reduced. No major kinematic differences were found when the lift assist device was worn indicating that it did not alter these specific technique variables. INTERPRETATION: The lift assist device did reduce the required muscular effort of the lumbar and thoracic erector spinae without adversely affecting the level of abdominal muscle activity. This reduction may help reduce the risk of recurring back injuries or assist in the return to work phase, especially in repetitive tasks.

Adult↗

PubMed2005

Differentiating lifting technique between those who develop low back pain and those who do not.

BACKGROUND: No research to date has been able to discriminate differences in lifting technique for healthy individuals who eventually develop low back pain compared to those that do not while employed in a manual materials handling industry. The purpose of this study was to demonstrate the ability of principal component analysis to identify differences in lifting technique. METHODS: Principal component analysis was applied to sixteen kinematic and kinetic waveforms describing the two-dimensional motion of the trunk and load. The principal component scores for each variable were used as the dependent measures in a one-way ANOVA to determine group differences. FINDINGS: Significant group differences (P<0.05) were found for five of the principal component scores capturing associated kinematic waveform patterns related to the control and placement of the box on the shelf, and associated kinetic waveform patterns related to the relative timing of extension moment generation in the sacral and thoracic regions. A related waveform pattern for trunk compression was also found. INTERPRETATION: Due to the coordinated movements involved in tasks such as lifting, differences among clinical populations have been difficult to demonstrate empirically. We were able to identify different characteristics in lifting kinematics and kinetics prior to the development of low back pain. Principal component analysis was able to identify important biomechanical differences where traditional analyses failed. This is the first study to identify such lifting differences prior to the development of low back pain.

Diagnosis, Computer-Assisted↗

PubMed2004

The effect of simulated school load carriage configurations on shoulder strap tension forces and shoulder interface pressure.

Recently, several studies have addressed the physical demands of school student's load carriage, in particular the load weight carried, using physical demands indicators such as oxygen consumption, gait, and posture. The objective of this study was to determine the effects of different load carriage configurations on shoulder strap tension forces and shoulder interface pressure during simulated school student's load carriage. A load carriage simulator was used to compare shoulder strap forces and shoulder pressure for 32 combinations of gait speed, backpack weight, load distribution, shoulder strap length and use of a hip-belt. The results showed that the manipulation of backpack weight, hip-belt use and shoulder strap length had a strong effect on shoulder strap tension and shoulder pressure. Backpack weight had the greatest influence on shoulder strap tension and shoulder pressure, whereas hip-belt use and then shoulder strap adjustment had the next greatest effects, respectively. While it is clear that researchers and practitioners are justified in focusing on load magnitude in backpack studies as it has the greatest effect on shoulder forces, hip-belt use and shoulder strap adjustment should also be examined further as they too may have significant effects on the demands placed on backpack users. Based on the present findings, school students should wear their backpacks with the least weight possible, use the hip-belt if present, allow a reasonable amount of looseness in the shoulder straps and should position the heaviest items closest to their back. However, more detailed work using human participants needs to be undertaken before these recommendations can be confirmed.

Back Pain↗

PubMed2004

Development and assessment of the Canadian personal load carriage system using objective biomechanical measures.

The Defence Research and Development Canada--Toronto managed a collaborative team of designers, biomechanists, ergonomists and military stakeholders in the development of a new personal load carriage (LC) system for the Canadian Forces. Ergonomics design principles using objective measurement tools and user-centred feedback from soldiers were considered essential to system development. The purpose of this study was to provide a detailed report of contributions by biomechanical testing to the final design of the final Canadian LC system. The Load Carriage Simulator and Compliance Tester were used to test design iterations of: three fragmentation vests, seven tactical vests and three iterations of the backpack. Test data were compared to a data pool of seventeen previously tested systems. Results indicated that the objective measures helped the design team by: (1) quantifying and understanding the consequences of various design changes; (2) predicting soldiers' responses to design changes in skin contact pressure, force and relative motion; (3) objectively comparing design iterations to other systems; and (4) providing information quickly so that ideas and recommendations could be incorporated into the next design iteration. It was concluded that objective assessments added valuable information not easily interpreted from human trials. However, objective assessments cannot replace human trials for feedback on functionality and features.

Anthropometry↗

PubMed2004

Are children's backpack weight limits enough? A critical review of the relevant literature.

STUDY DESIGN: Literature review. OBJECTIVE: To examine the epidemiologic, physiologic, and biomechanical literature that has contributed to the suggested weight limit of 10 to 15% body weight for children's backpacks. SUMMARY OF BACKGROUND DATA: The majority of children use a backpack to transport their belongings to and from school on a daily basis; however, controversy exists over the safety of backpack use and backpack loads. METHODS: A thorough review of the literature was completed to examine the appropriateness of the suggested weight limits and to determine future areas of research needed to increase the safety of children's backpacks. RESULTS: Epidemiologic, physiologic, and biomechanical data support the suggested weight limit of 10% to 15% body weight. CONCLUSIONS.: Based on the current literature, the value of 10% to 15% body weight is a justified weight limit; however, further research is required to determine the association between backpack use and injury and how the factors of load, backpack design, and personal characteristics, such as physical fitness, interact and influence the adaptations required when carrying a backpack.

Body Weight↗