GROUND REACTION FORCE PATTERNS FOR THE EVALUATION OR MOTOR RECOVERY IN ATHLETES AFFECTED BY KNEE INJURIES

Abstract

INTRODUCTION Vertical jump is an exercise widely adopted to evaluate some motor characteristics of the athletes. Vertical component of the ground reaction force (VGRF) is often used to gain more information regarding efficiency and motor coordination of the lower limbs. The aim of this study is to evaluate vertical jump performances of subjects afflicted by ACL injury, by means of VGRF patterns. METHODS Ten healthy rugby players (HP) were the sample of this study, together with four subjects who present a ACL pathology (PP), due to a previous injury. At the time of the acquisition all the pathological subjects had been reintegrated in the team training and competitive programs. The subjects were asked to perform 20 two-legged vertical jumps, as high as possible, keeping one foot at a time over a Kistler force platform. Arms were behind their back, in order to minimize the contribution of the upper part of the body to the thrust of the legs. Ground reaction forces were recorded by means of a force platform at the sampling rate of 1000 Hz, and data were normalized in amplitude to the body mass. Jumping height was computed through the flight time. RESULTS In agreement with previous studies, a common pattern in the GRF for HP subjects was observed; the typical VGRF time course was characterized by an initial decrease of the force until a minimum, followed by two maxima with a further relative minimum in between, the first peak is the absolute maximum. Amplitude and timing of these parameters were examined for the analysis. The mean jump height evidenced statistical diierences only between one PP subject and the mean jump height of the HP group. By considering VGRF amplitude, significative differences have been found only between the amplitude of the first minimum (healthy = 0.25 BW, pathological = 0.36 BW) while no differences were found between the absolute maxima. By considering the timing of the different phases it has been observed that PP group show a longer delay between the initial minimum and the first maximum. As far as the VGRF time course is concerned, we noted for PP subjects individual behaviors in comparison with the average pattern of the HP. Furthermore, the presence of a strong asymmetry between the curves of the healthy and pathological limb, were observed. CONCLUSIONS Jumping height does not seem to be a parameter useful in designating motor impairments in subjects with ACL injuries. However, as far as the VGRF is concerned, intra and inter individual significative differences may be observed. A common characteristics of PP group is the reduced capacity to perform the eccentric phase. While the amplitude of the maxima is similar, VGRF patterns of the PP group show individual characteristics and appreciable asymmetries between the two legs. These results allow to speculate about compensatory motor actions and confm that the majority of the PP subjects were from a complete motor recovery.