An investigation of changes in biomechanical strategies over extended lifting periods
Fogleman, Maxwell Tod
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Research on extended lifting periods has focused on the physiological and psychophysical effects of prolonged lifting; however, there has been little research done that documents the biomechanical effects of extended lifting periods. The research results presented here were a documentation of the changes in selected kinematic and kinetic parameters over extended lifting periods. Also, the effects of training on the development of long-term biomechanical strategies were investigated. Six male subjects were asked to lift a weight (determined by each subject) at the rate of one lift per minute for four hours. After this initial four-hour session, each subject lifted under the same conditions for six half-hour training sessions spaced across two weeks. After these training sessions, each subject lifted, again under the same conditions, for another four-hour period. Therefore, the effects of both extended lifting periods and training (practice) could be investigated. The effects of these conditions on two sets of response variables were analyzed. The first set was referred to as the primary response variables and consisted of the empirical objective function value, the time per lift, the minimum height at the hip, the maximum moment at the hip, the distance traveled by the load, and the distance traveled at the hip. The second set of response variables were the maximum moments exerted at the elbow, shoulder, hip, knee, and ankle. Results indicated that there were significant trends (as determined by the Cox and Smart test for trend) during at least one of the training conditions for the empirical objeaive function value (decreasing), time per lift (decreasing), the minimum hip height (increasing), and the maximum hip moment (increasing). The distance traveled by the load and at the hip did not consistently show significant trends for all subjects. Furthermore, the empirical objective function value, the time per lift, the maximimi hip moment, and the load travel distance all showed training effects as determined by the ANOVA. The maximum moments at the five joints showed training effects, but only the moment at the hip showed an effect due to the extended lifting period (the lift number). The implications of these results were that there is an development of strategies across extended lifting periods that involves the decrease in the time per lift and the increase in the maximum moments at all joint. However, the immediate response of naive lifters who are allowed to lift freestyle is to use the hip joint to absorb the greater dynamic moment required by a shorter time per lift. This inference is made since the moments increased at the hip only due to the lift number. However, when the subjects were allowed to practice, the moments at all joints increased, showing that stresses (moments) were distributed across all joints to accommodate the shorter time of the lift.