Monitoring Of Sprinters' Motor Coordination Through Vertical Jump Exercises

Abstract

Vertical jumping exercises are widely used in sport activities to estimate the motor condition of the athletes. Common methodologies, based on devices designed to compute the jumping height, seem to be not adequate in order to monitor the motor coordination status as function of training programs. This is particularly true when high level athletes, practising sports where functional qualities must be maximally developed, are considered. The aim of this study is to analyse the motor coordination patterns by means of mechanical net moments and powers, expressed at the main lower limb joints, during vertical jumping exercises. Subjects of the study were nine male sprinters (range of best performance on 100 m. = 10".4 - 10".8). The athletes were asked to jump as high as possible while keeping the hands on their hips, and performed jumps either with the thrust of both legs or the thrust of one leg. Data of four trials per condition and legs were recorded. Kinematic data, concerning the spatial position of ten 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 centers, such as the corresponding moments and powers, were estimated by using a special software (SAFLO) which inputs were anthropometric, kinematic and kinetic data. When necessary, non parametric statistics (Spearman rank correlation coefficient, Wi1coxon-MannWhitney test) were used to avoid the assumption of normal distribution of the underlying population. By considering intra-individual data the results show quite low subject variability in kinematics and ground reaction forces for all trial conditions. There is an appreciable variability of moment and power maxima at all the joints and this variability is not random but has high degree of covariance. Furthermore asymmetries have been evidenced between the mechanical output at the same joint both during bilateral and unilateral exercises. By considering interindividual data it has been found a wide spectrum of motor strategies evidenced by peaks amplitude and time sequence distribution. This biomechanical approach seems to be an appropriate tool to quantify important motor differences, not evidenced by the measurement of the gravity center displacement.