The effects of short-term resistance program on vertical jump ability in elite male volleyball players during the competition season

The aim of this study was to describe the effects of 6 weeks of combined strength and jump training which incorporated moderate loads and high intensity contractions on the vertical jump ability (VJ), loaded jumps and velocity of execution in full squat in a group of professional male volleyball players during the competition season. It was hypothesized that the VJ improved by cross combined strength and jump training both characterized by high velocity of execution (>1 m/s). The participants in this study were twelve players who competed in the first national division of the Spanish National League during the 2011-2012 season. The neuromuscular performance was estimated by unloaded (CMJ) and loaded countermovement jumps (CMJ(loaded)) height (cm); and by velocity of displacement in the concentric phase of full squat (FS) (m/s). There was a significant increase in CMJ and CMJ(loaded) after 6-week of training (5%, p<0.01; and 5.7%, p<0.05; respectively). These changes were accompanied by a small and moderate value of Effect Size (0.47, and 0.67; respectively). No significant differences were observed for velocity of displacement in FS. The linear correlation analysis showed a single moderate correlation statistically significant between the changes in CMJ-CMJ(loaded) and CMJ-FS (r=0.62 and r=0.59, p<0.05; respectively). Albeit speculative, our results suggest that the use of moderate loads could be enough to improve the vertical jump performance, since in our study a load equivalent to 60% IRM in the FS was not exceeded and jumping exercises were performed with light loads.