Maturational and situational determinants of reaching at its onset

• Infant reaching kinematics was measured on the average 2 days after reaching onset.
• Girls reached more, had straighter reaching and fewer movement units than boys.
• Anthropometrical differences did not influence reaching kinematics.
• Infants reached straighter in reclined position but without interaction with gender.
• Reaching performance was primarily determined by maturation.

At 3 months of age, reaching behavior was measured in a group of 10 girls and 10 boys born at term. The assessments were carried out on the average 2 days after reaching onset. Reaching kinematics was measured in both supine and reclined positions. Girls reached more than boys, had straighter reaching trajectories and movements of shorter durations as well as fewer movement units. The reclined position gave rise to straighter trajectories in both girls and boys. Several anthropometric parameters were measured. Girls had less length and volume of the forearm than boys but similar upper arm volumes. There was a weak relation between kinematic and anthropometric variables.