In this study we used a biofeedback system to evaluate the joint movements of 3-month-old infants in real-time. The computer was set to discriminate a specific leg position as the motor task infants had to discover to receive the reinforcement from a mobile. Two groups of infants were given two different tasks: (1) to cross 85° knee flexion in the flexion group, and (2) to cross 35° knee extension in extension group. The results from this experiment suggest that infants in both groups learned the task; however, they used different motor solutions. Infants in the flexion group demonstrated two distinctly different motor solutions to make the mobile move. One was movement-based and was characterized by an increase in kicking frequency, while the other was posture-based. In contrast, most infants in the extension group only used the movement-based solution to gain the reinforcements. Controlling the knee at the 35° extension positions seems to be more difficult than at the 85° flexion positions for 3-month-old infants. These results indicate that infants are capable of discovering narrowly defined leg motor solutions and that, depending on their individual characteristics and the task demands, they select different motor solutions.
Rosa M. Angulo-Kinzler, Beverly Ulrich and Esther Thelen
Rosa M. Angulo-Kinzler, Stephen B. Kinzler, Xavier Balius, Carles Turro, Josep M. Caubet, Josep Escoda and J. Antoni Prat
This study explains the general aspects of the biomechanics of the pole vault and presents a 3D analysis of the best official performances of the top 8 pole vaulters at the 1992 summer Olympic Games in Barcelona. Two time code synchronized S-VHS video cameras operating at 50 Hz were used. All vaulters showed a reduced last stride and a low CM during the penultimate foot support. Great horizontal velocity at takeoff, high grip, and well timed angular momentum serve as good indicators of a jumper's performance. An early positioning of the hips parallel to the bar can be very beneficial, as can a close placement of the CM to the bar at the time of pole release. Finally, an advantageous bar clearance technique used by the winning Unified Team vaulters is noted.