Countermovement Jumps in Pre-School Children Aged 3 to 6 Years: How Much Can Arm Swing Help in Performance?

Vertical jumping is a fundamental motor skill that develops rapidly in early childhood, yet the biomechanical contribution of arm swing in preschool-aged children remains unclear. This study aimed to investigate how arm swing influences countermovement jump (CMJ) performance in typically developing children aged 3 to 6 years. A total of 411 children (53.5% girls; mean age: 4.9 ± 1.1 years) from four European cities participated in this cross-sectional study. Each child completed five CMJs with and without arm swing using the Optojump system, measuring variables such as jump height, flight time, contact time, power, the reactive strength index (RSI), pace, and verticality. The results revealed a significant increase in jump height when using arm swing for both boys (+15%) and girls (+12.5%) (<i>p</i> < 0.001), yet power output, the RSI, pace, and verticality decreased significantly (<i>p</i> < 0.05). These findings suggest that preschool children are not yet biomechanically efficient in integrating arm movements into vertical jumping due to immature neuromuscular coordination. Although arm swing improves jump height, it does not enhance overall movement efficiency at this developmental stage. This study highlights the need for multidimensional and age-appropriate assessment protocols to better understand motor integration during early childhood.