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 ± 1.62 cm, 40%: 64.77 ± 2.36 cm). The TOV at 30% (2.73 ± 0.34 m·s) was significantly greater than that at 0% (2.59 ± 0.39 m·s) and 10% (2.63 ± 0.34 m·s), whereas that at 40% (2.79 ± 0.43 m·s) was significantly greater than that at >0, 10, and 20%. The rGRF at 30% (18.62 ± 4.35 N·kg) was significantly greater than that at >0, 10, and 20%, whereas that at 40% (21.38 ± 5.21 N·kg) was significantly greater than in all conditions. The RIF at 20, 30, and 40% (40%: 61.60 ± 18.53 N·kg) was significantly greater than that at 0% (44.46 ± 9.12 N·kg). The DV at 20% (2.61 ± 0.31 m·s) was significantly greater than at 10%, whereas those at 30 and 40% (2.8 ± 0.41 m·s) 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.
Exercise‐induced muscle injury is associated with performing exercise that involves eccentric contractions. Although the effects of eccentric exercise on muscle injury are well known, previous ...studies investigating muscle blood flow following eccentric exercise have revealed conflicting results. The purpose of this study was to examine forearm muscle blood flow (FBF) during submaximal handgrip exercise following eccentric exercise of the elbow flexors. Seven healthy male subjects (27.9 ± 3.7 yrs; ± SD) performed two bouts (5 min) of dynamic handgrip exercise at 10% of maximal handgrip strength before and 48 hrs following damaging exercise (2 × 25 maximal eccentric contractions). Mean blood velocities (MBV) were measured continuously in the brachial artery using Doppler ultrasound. FBF was calculated using arterial diameters obtained at rest (Pre; 4.06 ± 0.34 mm: Post; 4.21 ± 0.30 mm, p>0.05). Despite a significant decrease (p<0.05) in maximal biceps brachii isometric strength from pre‐ (16.9 ± 3.6 kg) to post‐injury (12.9 ± 4.6 kg), there was no difference in FBF at rest (Pre; 15.7 ± 4.1 ml/min: Post; 18.4 ± 5.4 ml/min) or at end exercise (Pre; 144.9 ± 34.7 ml/min: Post; 158.3 ± 28.4 ml/min) between conditions. It is concluded that muscle injury does not alter FBF during submaximal handgrip exercise suggesting that mediators involved in muscle injury and repair do not contribute to the regulation of muscle blood flow.
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