Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Kinesiology

First Advisor

Arnold G. Nelson

Abstract

Two experiments examined the acute effects of passive muscle stretching on the performance of a skill (vertical jump) which takes advantage of the stretch-shortening phenomenon. Because recent work suggests that passive stretching might impede the mechanisms (elastic and myoelectrical potentiation) thought to be responsible for this phenomenon, it was hypothesized that stretching would decrease the jump height of jumps executed with a preparatory countermovement (CMJ), but not the jump height of those initiated from a static, squatting position (SJ). In the first experiment, subjects performed CMJ and SJ jumps under two different conditions: after passively stretching the knee and hip extensors, and after 10 minutes of quiet sitting. As predicted, stretching induced a significant decrease (p $<$.05) in jump height for the CMJ; however, a similar decrease (p $<$.05) also occurred for the SJ. These results suggest that the influence of acute stretching on performance is not limited to skills which incorporate a stretch-shortening cycle, and that stretching does not necessarily impede the factors purported to be responsible for the stretch-shortening phenomenon. Experiment 2 sought to explicate the reasons why an acute bout of passive stretching can negatively impact jumping performance. Specifically, the aim was to determine if stretching could modify musculotendinous stiffness and/or electrical activity of the plantar flexors during both stretch-shortening movements and movements involving purely concentric contractions. Again, jumps performed with a countermovement were compared to static jumps; however, in order to isolate the plantar flexors, motion was restricted to the ankle joint only. CMJ jump height was compromised after stretching but SJ performance remained unchanged. The decrease in CMJ performance might be partially accounted for by a reduction in elastic potentiation, because a decrease in musculotendinous stiffness was also observed post-stretching. No change in electrical activity occurred between the pre- and post-stretch conditions for the CMJ, suggesting that a decrease in myoelectrical potentiation did not contribute to the performance decrement. Other potential mechanisms which might have played a role in reducing performance are discussed in addition to possible reasons why the stretching treatment influenced SJ performance differently in the two experiments.

ISBN

9780591591224

Pages

148

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