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J Strength Cond Res 24(1): 207-212, 2010--The purpose of this study was to quantify the vertical ground reaction forces (VGRFs) developed during the performance of popular bilateral plyometric movements. Fourteen power-oriented track and field men of collegiate and national level randomly performed 3 trials of 9 different bilateral plyometric exercises in a single testing session. Three depth drop (DD) and 3 depth jump (D J) conditions from 30, 60, and 90 cm heights (DD30, DD60, and DD90 and D J30, D J60, and D J90) were tested, in addition to vertical jump (VJ), standing long jump (SLJ), and 2 consecutive jump (2CJ) conditions. Peak impact VGRFs were normalized to body weight. Additionally, all conditions were compared against the VJ in an intensity index. The SLJ condition resulted in a significantly higher peak VGRF than the 2CJ condition (p [less than or equal to] 0.05). 9ODD, 90DJ, 60DD, and SLJ had a significantly greater peak VGRF (5.39, 4.93, 4.30, and 4.22 times body weight, respectively) than the VJ condition (3.34 times body weight). The 30DJ condition had an insignificantly smaller peak VGRF (2.78 times body weight) when compared with the VJ. Practitioners may use these findings to more effectively progress athletes in these movements based on their intensities. KEY WORDS biomechanics, kinetics, stretch-shortening cycle

This study investigated the effects of ballistic resistance training and strength training on muscle fiber composition, peak force (PF), maximal strength, and peak power (PP). Fourteen males (age = 21.3 [+ or -] 2.9, body mass = 77.8 [+ or -] 10.1 kg) with 3 months of resistance training experience completed the study. Subjects were tested pre and post for their squat one-repetition maximum (1RM) and PP in the jump squat (JS). Peak force and rate of force development (RFD) were tested during an isometric midthigh pull. Muscle biopsies were obtained from the vastus lateralis for analysis of muscle fiber type expression. Subjects were matched for strength and then randomly selected into either training (T) or control (C) groups. Group T performed 8 weeks of JS training using a periodized program with loading between 26 and 48% of 1RM, 3 days per week. Group T showed significant improvement in PP from 4088.9 [+ or -] 520.6 to 5737.6 [+ or -] 651.8 W. Rate of force development improved significantly in group T from 12687.5 [+ or -] 4644.0 to 25343.8 [+ or -] 12614.4 N x [s.sup.-1]. PV improved significantly from 1.59 [+ or -] 0.41 to 2.11 [+ or -] 0.75 m x [s.sup.-1]. No changes occurred in PF, 1RM, or muscle fiber type expression for group T. No changes occurred in any variables in group C. The results of this study indicate that using ballistic resistance exercise is an effective method for increasing PP and RFD independently of changes in maximum strength (1RM, PF), and those increases are a result of factors other than changes in muscle fiber type expression. KEY WORDS training, resistance, isometric, jumping, force

The article discusses the importance of Power Balance bracelet from the Power Balance Inc`. It states that the said bracelet has two dime-sized holograms that are designed to resonate with and respond to the natural energy field of the body. It mentions that the said bracelet can improve trunk flexibility, balance, strength and lower body power.