Environmental illumination and target object size effects on reach-to-grasp movement for young and old adults

The reach to grasp movement is a daily functional human activity necessary for interacting with the environment. However, how indoor lighting conditions and the target object size impacts the reach to grasp movement motor strategy remain ambiguous. This study therefore elucidates the environmental illumination and target object size effects on human reach to grasp movement. 16 young (averaged age 22.1 ± 1.2 years) and 16 older adults (averaged age 72.3 ± 4.0 years) were recruited to participate in this study. Five illumination levels including 50, 150, 300, 500 and 750 lx (with the color temperature was 4000 k) and cylinders with five sizes 0.5 × 0.5, 1.0 × 1.0, 2.0 × 2.0, 3.0 × 3.0 and 5.0 × 5.0 (diameter × height; Φ × h; centimeters) cm were randomly used. An ultrasonic three-dimensional motion analysis system (Zebris CMS-HS, Zebris Medical GmbH, and Germany) was used to collect the relevant kinematics of wrist, grip aperture, joint range of motion of wrist and elbow and reaction time. The results indicated that environmental illumination did not have a significant influence on the reach to grasp motor strategies (p > 0.05). The target object sizes had a remarkable effect on the kinematics of wrist, grip aperture, joint range of motion and performance time for both age groups (p < 0.05). Differences were found between young and old adults on the kinematics of wrist, grip aperture, joint range of motion on wrist and elbow and time of grasp to return (p < 0.05). The contributions of this study provide useful information to understand the environmental illumination and target object size influences on reach-to-grasp movement.