Abstract

To investigate the influence of strength training on the electrical and mechanical behavior of leg extensor muscles during concentric and various stretch-shortening cycle exercises, eleven male subjects went through dynamic heavy resistance strength training with loads of 70 to 120 one maximum repetition three times a week for 24 weeks. The heavy resistance strength training resulted in specific changes in the neuromuscular performance. This was demonstrated by the great shifting of primarily the high force portions of the force-velocity curves measured both during the squat (SJ) and counter movement jumping (CMJ) conditions. An increase of 30.2 in maximal strength was noted during the training, while the increases became gradually smaller near the high velocity portions of the curve, where an increase of 7.3 in the jumping height in SJ and a non-significant increase in the maximal extension velocity with free loads were noted. The increases in positive work phases of force production were accompained by significant increases in the neural activation (IEMG) of primarily the vasti medialis and lateralis muscles, while only slight changes were noted in the RF muscle. Only minor and mostly nonsignificant changes were observed during the strength training in the neural activation and force production of the leg extensor muscles in various drop jumps, in which high contraction velocities are utilized. When the training was followed by a 12-week detraining, a great decrease in maximal strength was observed, while the changes in various parameters of explosive force production were either small or nonsignificant. The present findings regarding the changes in the electrical and mechanical behavior of the leg extensor muscles during heavy resistance strength training give additional support for the concept of specificity of training. Verf.-Referat