The experiment presented here was conducted for the purpose of investigating changes in lifting patterns that occur due to the effects of learning and due to the effects of lifting over extended periods. It also illustrated the use of biomechanical measures in tracking these changes. Biomechanical measures usually have not been used to make interences about changes in lifting patterns due to such effects as practice, the number of lifts performed in a session, the frequency of lifting, etc. Six inexperienced subjects were asked to lift for an initial 4-hour session, six half-hour practice sessions, and a final 4-hour lifting session. All lifts were conducted at the rate of one lift per minute, from floor to shoulder height, with a weight chosen by the subject. Results indicated that there is a change from a leg lift to a more biomechanically stressful back lift (as inferred from greater joint center moments) due to the effects of training, but once these effects are observed they were maintained through the second 4-hour session. Furthermore, reduction in time per lift over the course of the experiment was accompanied by increases in moments at all of the joint centers, but this was more pronounced in the hip and knee joints for half of the subjects. Conclusions to be drawn from these results are that biomechanical modeling can be used under such circumstances with meaningful results and that there is a natural tendency to lift more quickly and to shift moments to the stronger muscles in the process of learning lifting patterns.
- Forward dynamics
- Inverse dynamics