EFFECTS OF DIFFERENT ELASTIC CORD ASSISTANCE LEVELS ON VERTICAL JUMP TAI T. TRAN,LEE E. BROWN,JARED W. COBURN,SCOTT K. LYNN,NICOLE C. DABBS, MONICA K. SCHICK,EVAN E. SCHICK,ANDY V. KHAMOUI,BRANDON P. URIBE, AND GUILLERMO J. NOFFAL Center for Sport Performance, Human Performance Laboratory, Department of Kinesiology, California State University, Fullerton, California ABSTRACT Tran, TT, Brown, LE, Coburn, JW, Lynn, SK, Dabbs, NC, Schick, MK, Schick, EE, Khamoui, AV, Uribe, BP, and Noffal, GJ. Effects of different elastic cord assistance levels on vertical jump. J Strength Cond Res 25(12): 3472–3478, 2011—Currently, little research has been conducted using body weight reduction (BWR) as a means to enhance vertical jump. The purpose of this study was to determine the effects of different elastic cord assistance levels on vertical jump height (JH), takeoff velocity (TOV), relative ground reaction force (rGRF), relative impact force (RIF), and descent velocity (DV). Thirty recreationally trained college men and women (M = 15, W = 15) completed 3 testing sessions consisting of 5 conditions: 0, 10, 20, 30, and 40% BWR. In all BWR conditions, the subjects wore a full body harness while being attached to 2 elastic cords suspended from the ceiling and a linear velocity transducer. They then performed 3 maximal countermovement jumps with arm swing on a force plate. The results indicated no interaction of condition by sex for any variable; however, there was a significant (p , 0.05) main effect for condition for each variable. The JH significantly increased across all conditions (0%: 43.73 6 1.62 cm, 40%: 64.77 6 2.36 cm). The TOV at 30% (2.73 6 0.34 mÁs 21 ) was significantly greater than that at 0% (2.59 6 0.39 mÁs 21 ) and 10% (2.63 6 0.34 mÁs 21 ), whereas that at 40% (2.79 6 0.43 mÁs 21 ) was significantly greater than that at .0, 10, and 20%. The rGRF at 30% (18.62 6 4.35 NÁkg 21 ) was significantly greater than that at .0, 10, and 20%, whereas that at 40% (21.38 6 5.21 NÁkg 21 ) was significantly greater than in all conditions. The RIF at 20, 30, and 40% (40%: 61.60 6 18.53 NÁkg 21 ) was significantly greater than that at 0% (44.46 6 9.12 NÁkg 21 ). The DV at 20% (2.61 6 0.31 mÁs 21 ) was significantly greater than at 10%, whereas those at 30 and 40% (2.8 6 0.41 mÁs 21 ) were significantly greater than at 0, 10, and 20%. These results demonstrate that using different elastic cord levels to reduce body weight appears effective for increasing ascent and descent force and velocity variables. Future research should investigate greater BWR% and chronic training. KEY WORDS impact, harness, velocity INTRODUCTION L imb speed is an important component in vertical jump; however, there are many factors that contribute to an athlete’s increased vertical jump height (JH). Jumping faster than accustomed may develop greater takeoff velocity (TOV), which may lead to a greater JH. However, little is known about using elastic cords to assist jumping, via increased TOV resulting from increased ankle, knee, and hip joint speed. Using different levels of elastic cord tension may result in different outcomes because how this assistance affects jump mechanics is not well understood. In a related area, such as overspeed sprinting, common training methods to increase limb speed vary between downhill sprinting (10,11,23), treadmill sprinting (24), assisted towing (28), or resisted towing (8,19). A number of assisted training studies have successfully decreased sprint time using overspeed training (9,11,23,28). The theory is that running faster than accustomed will develop increased speed via increased step frequency and stride length (8,23). This overspeed theory may also be applied to vertical jumping, because JH is strongly related to TOV. Previous research using different levels of assisted jumping via elastic cord as an overspeed method has reported acute increases in vertical JH, peak velocity, peak acceleration, and relative peak power (1,7,14,21,27). These devices reduce body weight via elastic cords thereby increasing TOV and allow individuals to jump higher. A study by Imachi et al. (14) reported that male volleyball players increased JH after 10 weeks of body weight reduction (BWR) assisted training. They showed that the 10 and 20% BWR groups had an increased JH of approximately 8–10 cm compared with only 3.5 cm for the body weight group. Sheppard et al. (27) reported that after 5 weeks of assisted training with an absolute unloading of 10 kg resulted in increased peak Address correspondence to Lee E. Brown, leebrown@fullerton.edu. 25(12)/3472–3478 Journal of Strength and Conditioning Research Ó 2011 National Strength and Conditioning Association 3472 Journal of Strength and Conditioning Research the TM Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.