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The Effects Of External Load On Vertical Jump Peak Power And Eccentric Utilization Ratio

Hellberg, Peter; Hartman, Michael J; Winchester, Jason B

The Journal of Strength & Conditioning Research: January 2010 - Volume 24 - Issue - p 1
doi: 10.1097/01.JSC.0000367125.20015.fc

The ability to utilize the stretch shortening cycle (SSC) efficiently is a critical factor for success in many sports that involve sprinting, jumping, and production of maximal muscular power. Given the advances of sports equipment, many athletes are now wearing protective clothing or equipment while participating in competitive or recreational sports. It is not known to what extent the use of protective equipment, or application of the equipment as an external load, may have on the SSC or sports performance. The purpose of this research was to examine the influence of external loading on vertical jump and SSC performance in recreationally active college-aged adults. Twenty-four subjects (12 male, 12 female) who routinely participate in recreational sports or exercise volunteered for this study. Vertical jump height was determined using a static jump (SJ) and counter movement jump (CMJ) using a contact-mat under normal and loaded conditions. An external load equal to 5% of the subject's body mass was applied via a weighted vest. Following a standardized warm-up, subjects were allowed one practice jump at each condition. Subjects maintained a hands-on-hip position in order to concentrate on hip-leg power and minimize jumping technique differences resulting from arm swing. Three trials were given for each condition, with instruction to obtain maximal height on each jump. Peak power was estimated from vertical jumps using the equation developed by Sayers et al. [PP (W) = (60.7) × jump height (cm) + 45.3 × body mass (kg) -2055]. The reliance of SSC was determined using the eccentric utilization ratio (EUR), which is derived from the difference between SJ and CMJ and was determined under both conditions. A repeated measures ANOVA was used to determine group differences and differences between jumps and loading conditions. There were significant differences in jump performance (p < 0.05) between males and females as such all results are analyzed by gender. Comparisons of jumps under different loading conditions determined that the application of external load significantly reduced jump height (p < 0.05) in SJ and CMJ for both groups, whereas peak power was only significantly reduced (p < 0.05) for CMJ in the male group. When subjects were tested for SSC utilization, the external load had a significant effect on EUR power in only the male group (1.37%; p = 0.02). Data from this investigation suggests that an external load, such as protective athletic equipment, may have an influence on vertical jump and SSC performance in recreational athletes. In males, an applied external load decreases CMJ power output and influences the ability to maximize the use of SSC. Given that the CMJ is a commonly used tool to assess performance capabilities, practitioners may wish to consider the addition of an external load while testing to more accurately reflect the conditions in which sport performance will occur for their particular event. Further investigation is needed to determine if the results from this study are consistent when testing highly trained athletes.

© 2010 National Strength and Conditioning Association