Effects of Time of Day and Warm-Up on Lifting Kinematics
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Date
2007-06-13
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Abstract
There is a real need to be able to understand the etiology of back injury. One area that has had only limited research is that of time of day effects. Previous studies have measured both the static (Adams et al., 1987) and dynamic (Fathallah et al., 1995) effects time of day has on the low back. These studies, however, measured maximum capabilities and did not relate their results to real world applications. The objective of the current study is to explore the effects that time of day and warm-up have on trunk kinematics during an industry inspired lifting task.
Nine male and three female subjects participated in the study. A series of four separate experimental sessions, two AM sessions held one hour after rising and two PM sessions held nine hours after rising, were performed. During one AM and one PM session the subject was led through a series of physical warm-up exercises prior to performing the lifting exertions. Upon conclusion of the warm-up, subjects completed a lifting task with two separate weight conditions, 3.6 kg and 10.9 kg. The lifting task consisted of lifting a box from the floor, rotating approximately 130°, and placing the load on an adjacent conveyer. Twenty consecutive lifts were completed for each load condition. The independent variables were SESSION (AM and PM), WARM-UP, and LOAD (low-3.6 kg and high-10.9 kg). The dependent variables considered in this study were peak trunk range of motion and peak trunk velocity in the sagittal and rotational planes, and the (x,y) coordinate positions of each knee in the anterior/posterior and lateral directions at the peak trunk position.
The experiment was of a split plot design and used MANOVA and subsequent univariate ANOVA to test for statistical significance. LOAD was the only independent variable that proved statistically significant, and was significant for trunk sagittal position, trunk sagittal velocity, and lateral knee position. Trunk sagittal position increased from 75 (±0.48)° to 78 (±0.50)° for the low and high conditions, respectively. Trunk sagittal velocity on the other hand decreased from the low (140 (±0.87)°/s) to the high (130 (±0.92)°/s) condition. Neither SESSION nor WARM-UP were found to affect these kinematics variables.
The lack of statistical significance could have occurred for several reasons. The current study chose to measure range of motion (ROM) while doing an industry inspired lifting task. In order to complete the task subjects were not necessarily required to use a full range of motion. Instead, they used only the range of motion needed to accomplish the task. Results showed that SESSION had little effect on this ROM. Subjects were also allowed to complete the lifting task in any way they chose, which introduced inter-subject variability to the experiment because no two subjects used the same lifting technique. Overall intra-subject lifting strategies did not change with regard to SESSION or level of muscle WARM-UP.
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Keywords
lifting kinematics, time of day, warm-up
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Degree
MS
Discipline
Industrial Engineering
