Comparative Analysis of Infant Lifting Tasks and Weight Effects on Postural Balance

Infant care activities, such as lifting and holding, impose mechanical and postural demands that may challenge caregivers’ postural balance. Little is known about how different infant lifting postures and weights affect dynamic postural balance. Sixteen healthy young adults performed three representative infant lifting tasks (underarm, supine, and piggyback lifting tasks) under two weight conditions (4.6 kg and 9.8 kg) using custom-designed infant dummies. Ground reaction forces were measured for 60 s using a force platform to obtain center of pressure (COP)-based sway variables, including mean velocity, mean distance, sway area, mean frequency, and peak power. Two-way repeated-measures ANOVA was used to examine the effects of lifting posture, dummy weight, and their interaction. Heavier infant weight significantly increased most COP variables, indicating reduced postural stability (P<0.05). Lifting posture significantly affected mean distance and mean velocity only under the lighter weight condition, where piggyback lifting produced greater sway size and speed than underarm and supine lifting. These task effects were most pronounced in the anteroposterior direction. Under the heavier load, no significant posture-dependent differences were observed (P>0.05). Posterior load placement, such as piggyback lifting, imposes the greatest mechanical challenge to postural balance control, while underarm and supine lifting postures demonstrate relatively stable balance profiles, particularly when handling lighter infants. These findings provide biomechanical evidence to support safer caregiving strategies and may inform ergonomic guidelines for infant handling and lifting.