Evaluating the Effects of Age on the Variability in Lifting Technique

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Title: Evaluating the Effects of Age on the Variability in Lifting Technique
Author: Freeman, Jacklyn H
Advisors: Dr. Peter Mente, Committee Member
Dr. David Kaber, Committee Member
Dr. Gary A. Mirka, Committee Chair
Abstract: As individuals age, they under go numerous changes that can affect their lifting technique. These changes include muscle strength and flexibility reductions, and decreases in postural control. The rate and degree of these declines vary from individual to individual, which can lead to variability in their lifting technique. The objective of this research was to evaluate the inter- and intra-subject variability of the trunk kinematics and ground reaction forces on the lifting technique used to perform a lifting task. Variability of the lifting technique is important to consider when evaluating the safety of lifting tasks. A higher variability of a lifting technique means that some individuals perform the lifting task using more extreme techniques than others. Thus, a lifting task with high variability can lead to a greater risk of injury if the variability is not taken into account when testing the safety of the lifting task. The hypothesis was that an older subject group would have a higher inter- and intra-subject variability than a younger subject group. It was hypothesized that older subjects would have greater inter-subject variability because of the varying experiences and backgrounds of the older subjects, which would lead to variances in the lifting technique between subjects. It was hypothesized that older subjects would exhibit greater intra-subject variability because older subjects are more likely to lose their balance during a lifting task and would experience weakened muscles faster than younger subjects, both of which would lead to variance in the lifting technique within a subject. Two subject groups were used in this study — a younger subject group and an older subject group. Subjects were asked to perform lifting tasks that included two levels of load and three levels of lifting asymmetry angle. Trunk kinematic data were captured using a Lumbar Motion Monitor, and ground reaction force data were captured with a force platform. The inter- and intra-subject variability of the trunk kinematic data and force platform data were calculated using equations derived from the Modified Levene's test. Two statistical models were created — one model for the inter-subject variability dependent variables and one model for the intra-subject dependent variables. Multiple Analysis of Variance (MANOVA) and subsequent univariate Analysis of Variance (ANOVA) techniques were used to analyze the effects of age, weight, and angle (and their interactions) on the dependent variables. The results did not support the hypothesis, as age was neither a significant main effect nor a factor in any significant interactions for any of the dependent variables. For inter-subject variability, the MANOVA showed that weight*angle was significant and for intra-subject variability, the MANOVA showed that angle was significant. The general trend of increasing intra-subject variability was demonstrated with increasing angle. One possible explanation for why age was not a significant factor in the inter-subject variability dependent variables is the relatively homogenous nature of the older subject group. An explanation for why age was not a significant factor in the intra-subject variability dependent variables is that since older subjects exhibit decreased flexibility, they were more constrained in how they performed the lifting task. Future work should consist of choosing a heterogeneous older subject group with varying backgrounds among subjects. Recording the flexibility and muscle strengths of all subjects would be beneficial for comparison between the older and younger subject groups.
Date: 2005-08-16
Degree: MS
Discipline: Industrial Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/1964

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