Aging effect on kinematics during prehension movement with obstacle

Twenty male with 15 young adults between 18 and 35 years (mean, 25.75 years ^ 4.41) and 5 senior between 65 and 74 years (mean, 69.5 years ^ 6.36) are asked to grasp an object and to put it in a final position without moving or touching the obstacle. The object is a polystyrene sphere with a mass fixed to 20 g and a diameter to 5.5 cm, placed at 50 cm in front of the participant. Different obstacle sizes (10, 15 and 20 cm) and width (3, 7 and 15 cm) are successively placed at 15 or 25 cm between the subject and the object. Each subject performs 39 trials (2 £ 9 obstacles £ 2 positions þ 3 controls) in a randomized order. The reference condition (control) consists in reaching the object without obstacle. A Vicone motion capture system (Oxford Metrics Inc.) and Cyberglove (Virtual Technologies, Alto Palo, CA) are used to track upper limb, hand and digits right movements. A 12 typical postures procedure is performed by each participant to calibrate the data glove. Three dimensional movements of the wrist are recorded, thanks to an electromagnetic sensor (The Flock of Birds, Ascension Technology, Inc. Burlington, Vermont, USA). The sampling frequency is 120 Hz for the Vicon and 64 Hz for the Cyberglove and the recording period is 6 s. Trajectories are filtered using a fourth order 6 Hz Butterworth filter. 3. Results and discussion