Electromyographic and Force Production Characteristics of Leg Extensor Muscles of Elite Weight Lifters During Isometric, Concentric, and Various Stretch-Shortening Cycle Exercises

Abstract

Electromyographic and force production characteristics of leg extensor muscles of elite weight lifters (n=14) were examined during isometric, concentric, and various stretch-shortening cycle exercises. The data showed that utilization of stored elastic energy of leg extensor muscles was observable in countermovement jumping (CMJ) conditions performed at various loads. These greater (P < 0.01-0.001) vertical jumping heights obtained in CMJ conditions in comparison to the respective squat jumps (SJ) took place at all loads examined from 0 up to 180 kg with no differences in the average IEMG activity between the concentric phases of the performances. In various dropping jumps (from 20 to 100 cm), the average jumping heights were not, however, greater than in the squat jump. The jumping heights both in SJ and CMJ correlated negatively (r = -0.56 and -0.58; P < 0.05) with the time of isometric force production. Maximal isometric force correlated (r = 0.61; P < 0.01) with the thigh girth but not (r = 0.22; NS) with the mean muscle fiber area of the vastus lateralis muscle. The jumping heights in SJ and CMJ performed with higher (100-140 kg) loads correlated more significantly (r = 0.76-0.79; P < 0.01-0.001) than that of maximal isometric force (r = 0.47-0.67; P < 0.05-0.01) with the results in the Olympic weight lifting. The present findings indicate the important role of effective recoil of the elastic energy in the muscle during the stretch-shortening cycle. The observations also specify the characteristic features of the neuromuscular performance capacity of the elite weight lifters and therefore support in part the concept of training and testing specificity.

Key words

isometric contraction - stretch-shortening cycle - weight lifting - electromyography - utilization of stored elastic energy