Effects of assistance with elastic cords on kinematics of vertical jumps
Abstract
Introduction and objectives: Plyometric training represents one of the best means to improve muscle power, particularly of the lower limbs. It seems there is no advantage in adding weight during this practice; however, when this is the case, preference should be given to light loads. In the 1990s, some practitioners began to suggest the opposite direction, reducing instead of increasing body weight with the use of elastic cords. The aim of this study was to compare the contact time, the flight time and the reactive strength index (RSI) in assisted and unassisted vertical jumps performed by experts in power events in athletics. Methods: Twelve international level athletes, six men and six women, aged 18-28 years, were submitted to the following measures: body weight, height, body mass index (BMI) and two consecutive vertical jumps with the aid of arm movement, under two conditions: with and without the assistance of elastic cords. The reduction in body weight was approximately 12kg at the assisted condition, or 15-20% of body weight. The variables were compared using Student t test, adopting a significance level of p ≤ 0.05. Cohen's d Effect Size was also calculated. Results: The flight time and the jump height increased on assisted condition in both sexes, without negative interferences on contact time. Conclusion: RSI tended to increase with assistance of elastic cords, maintaining the training specificity. The inclusion of this training mean in the routines of experts in power events in athletics is recommended.
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