Previous research has shown that an acute bout of passive muscle stretching can diminish performance in certain movements where success is a function of maximal force and/or power output. Two possible mechanisms that might account for such findings are a change in active musculotendinous stiffness and a depression of muscle activation. To investigate the likelihood of these two mechanisms contributing to a post-stretch reduction in performance, we examined the acute effects of stretching on the active stiffness and muscle activation of the triceps surae muscle group during maximal single-joint jumps with movement restricted to the ankle joint. Ten males performed both static (SJ) and countermovement (CMJ) jumps before and after passively stretching the triceps surae. Electrical activity of the triceps surae during each jump was determined by integrating electromyographic recordings (IEMG) over the course of the movement. Triceps surae musculotendinous stiffness was calculated before and after stretching using a technique developed by Cavagna (1970). Following stretching, a significant decrease [mean (SD) 7.4 (1.9)%; P<0.05] in jump height for the CMJ occurred, but for the SJ, no significant ( P>0.05) change in jump height was found. A small but significant decrease [2.8 (1.24)%; P<0.05] in stiffness was noted, but the magnitude of this change was probably not sufficient for it to have been a major factor underlying the decline in CMJ performance. Paradoxically, after stretching, the SJ exhibited a significant ( P<0.05) decrease in IEMG, but the IEMG for the CMJ remained unchanged ( P>0.05). It appears that an acute bout of stretching can impact negatively upon the performance of a single-joint CMJ, but it is unlikely that the mechanism responsible is a depression of muscle activation or a change in musculotendinous stiffness.
The purpose of this study was to examine the changes in coordination associated with practice of a soccer kick. Video records were collected on 6 novice, right-footed soccer players prior to and after 20 regularly scheduled kicking practice sessions. Three experienced players were also videotaped for comparison. Movement of the right leg was digitized and analyzed using motion analysis software. As a result of practice, subjects were able to significantly increase the maximum resultant linear velocity of the foot, and these increases were accompanied by changes in the pattern of coordination underlying the movement. These changes were assessed qualitatively through the topological characteristics of the relative motions of the hip and knee and quantitatively through three different timing variables. The results provide some support for Bernstein's (1967) ideas on the acquisition of skilled behavior as well as for the two-stage model of motor learning proposed by Newell (1985).
Structuring practice conditions for children should take into account task complexity and feedback frequency in determining the cognitive challenge necessary for optimal skill learning. More generally, the findings suggest that practitioners teaching motor skills should design practice conditions in accordance with the cognitive processing capacity of the learner.
Background and Purpose. Mental practice has been shown to be effective in increasing the force production of the abductor digiti minimi muscle in the hand. The aim of this study was to determine whether mental practice could produce strength gains in the larger ankle dorsiflexor muscles, which are important during walking. Subjects. Twenty-four subjects were randomly assigned to a physical practice group, a mental practice group, or a control group (8 subjects per group). Methods. In the practice groups, subjects either physically or mentally practiced producing maximal isometric contractions for 3 sets of 10 repetitions, 3 times per week for 4 weeks. Changes in mean peak isometric torque normalized to body weight and the resulting percentage of improvement were analyzed across the 3 groups. Results. Differences in raw torque production after training in the 2 practice groups resulted in significant percentages of improvement for the physical practice group (25.28%) and the mental practice group (17.13%), but not for the control group (−1.77%). The 2 practice groups were not statistically different in their maximal torque-generating capacity after training. Discussion and Conclusion. These findings show that mental practice in people without impairments can lead to an increase in torque production similar to that produced by physical practice. Such a technique may prove to be a useful adjunct to traditional treatment options aimed at increasing muscle strength.
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