It is often difficult to optimize strength qualities in-season due to the conflicting influences of extensive skill practices combined with frequent game play of the competition schedule. The purpose of this study was to investigate the effects of two interventions on strength qualities and CMJ performance. Thirteen women volleyball players competing in NCAA Division I were tested before and after four weeks of an inseason strength training program with emphasis on heavy squatting (6-IORM), and then before and after three weeks of unloaded jump training. Dynamic squat strength, isometric squat strength, optimal power, CMJ, SJ and approach jump and reach were all tested before and after both cycles. There was a significant increase in both average 1RM squat strength (5%) and vertical jump (1%) following the strength cycle. Following the unloaded training, there was a significant increase in both peak power output (18%) and peak velocity (14%) in the CMJ. SJ performance significantly increased in both peak force (6%) and maximum height (10%). Throughout training, there were no decreases in maximal strength levels or post-test Vertec jump and reach. This study indicates that heavy squatting can improve vertical jump as well as 1RM squat despite a high volume in-season practice and competition schedule. Furthermore, unloaded training can improve the explosive qualities of athletes when used as a peaking cycle late in-season. Athletes maintained dynamic strength and jumping ability from pre-testing scores, while significantly increasing both peak velocity and power in the CMJ. / School of Physical Education

The purpose of this study was to investigate two different plyometric training techniques for increasing vertical jumping ability. Twenty-four female high school volleyball players were matched for height and weight and distributed equally among three groups. Each subject performed a vertical jump test, Margaria power test, Wingate bicycle test, and an isokinetic leg strength test prior to and following six weeks of training. Plyometric training significantly (p<.05) improved vertical jumping ability and some indices of leg strength and power. Weighted plyometrics did not enhance performance more than plyometrics alone. These data support the view that plyometric training with or without added weights enhances vertical jumping and leg power.