LOWER LIMB KINETIC VARIABILITY IN VERTICAL JUMPING

Abstract

For more that 50 years vertical jumping exercises have been widely used in sport practice as a measure of power not only to predict athletic ability but also to obtain indications on same near-muscular and motor characteristics of the athletes. The most interesting work in this area has been done by a research group at the Free University of Amsterdam. The studies of these authors evidenced very elegantly that kinetic analysis provides potentially more diagnostic information force derived indices. However, what the majority of previous studies on human extremely large intra subject variability of the joint kinetic variables. So far, no attempts have been made to gain more insight into the variability inherent in moment and power selected measurements in vertical jumping exercises. To the best of our knowledge, in fact, all the studies employed on or more homogeneous subject groups and presented data describing the average performance groups. Furthermore, frequently, when mean values of kinetic parameters for a group were calculated, only the highest jump of each subject was selected for the calculation. The present experiments were devised to gain more insight into the variability of aforementioned biomechanical parameters in order to determine the appropriate number of trails necessary to obtain a stable mean for these parameters and to investigate the interday variability. Eight recreational athletes were the subjects of this study. In two different test sessions, each subject performed 25 double-legged countermovement vertical jumps without the arm swing. Kinematic data, concerning the spatial position often anatomical landmarks (five per each leg), were recorded by means of an optoelectronic system (ELITE) with a sampling rate of 100 Hz. Simultaneously, ground reaction forces were measured with a Kistler force platform at the sampling rate of 1000 Hz. The internal joint centres, such as the corresponding moments and powers, were estimated by using a special software (SAFLO) which inputs were anthropometric, kinematic and kinetic data. Preliminary results show that, considering all the subjects, power mean value stability ranges from 11 to 16 trials. Interday correlation was higher for hip and ankle and lower for knee values. These results suggest the need to adopt multiple trial protocols to reach reliable results suitable for identifying meaningful performance differences.