|dc.description.abstract||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.||