MECHANICAL MUSCLE PROPERTIES AFTER TWO TYPES OF PLYOMETRIC TRAINING

Abstract

Strength training effects may be highly specific. This suggestion is not always supported by previous research. Most training studies use strength measures to evaluate the effect of the program. It seems reasonable that a measure of strength does not fully describe the training adaptation. Therefore the design of this experiment is different. All subjects performed a set of 18 maximal contractions (isometric, isokinetic and plyometric) before and after training. Based on this set of measurements a mechanical muscle model was quantified. The coefficients of the model represent muscle properties which underlie force development (force-length, force-velocity relationship and contraction history). By studying the changes of the coefficients an attempt is made to speculate further on the underlying mechanisms which. may be responsible for the strength increase. The proposed study is designed to evaluate the use of a muscle model in investigating training programs. The subjects were divided in 3 groups: one control group (N=10) and two training groups (N=2*10). The training program involved plyometric contractions for the elbowflexors 3 dayslweek for a period of 6 weeks. These plyometric movements consisted of two successive contractions (concentric + kccentric) over an amplitude of 120" at 60"ls. The only difference between both training programs was the fact that sequence of those contractions was reversed namely concentric-eccentric for the CE-group and eccentricconcentric for the EC-group. The three groups (CE, EC. Control) showed no difference in isometric strength pre and post training. For the dynamic strength a significant improvement (P < 0.05) was observed only for both training groups. CE-training resulted in a significant change of the coefficients representing the force-velocity relationship (P < 0.05 for the ecc. part and P < 0.01 for the conc. part). The negative effect of a concentric contraction history was significantly reduced after the EC-training (P < 0.05). It can be concluded that both training groups made similar gains in dynamic force. However, analysis using the model showed that the cause of these force gains was different. For the CE-group the improvement in dynamic force can be attributed to an ameliorated force-velocity relationship whereas for the ECgroup this was due to a reduced influence of the concentric contraction historv. Specific changes in force development after training can be studied using a muscle model. These findings are a useful contribution in determining specific effects of training.