P3A288: Infant Rolling Coordination Depends on the Mechanical Environment

Background: In 2021, an estimated 15,000 injuries involving inclined nursery products were treated in emergency departments. A majority of injuries were caused when unrestrained infants rolled over or fell out of the products (CPSC, 2022). With infants spending a considerable amount of time in inclined environments, it is important to understand how an infant’s movements, including the ability to roll, may be affected by an incline. Previous research has identified six distinct coordinated techniques that infants use for rolling on a flat surface, named A-F (Kobayashi, 2016), but no studies have explored these movements on anything other than a flat surface. Therefore, the purpose of this study is to quantify how an infant’s coordinated rolling movements are affected by different mechanical environments.

Methods: Twenty-nine healthy infants (6.7±0.6 months, 16M/13F) participated in this IRB-approved study (126-MED20-005). Infants lay supine on a firm flat playmat and then in four device configurations unrestrained, in a random order. Each trial lasted for 5-minutes or until a complete supine to prone roll was achieved. The four device configurations, designed to represent common commercial infant products, featured a firm flat support with minimal soft goods and seatback angles of 0°, 10°, 18°, or 28°. The 0° configuration had a base angle of 0°, while the other three configurations had a base angle of 15° (Fig.1C). A GoPro camera recorded all trials. We used validated guidelines to characterize the six different coordinated rolling movements from video alone (Siegel, 2023, in-review). The rolling coordinated movements were then categorized by testing condition, and a Pearson Chi-Squared Test determined significant differences in proportions compared to the flat surface (p < 0.05).

Results: We analyzed 234 total rolling movements, defined as the supine to lateral torso rotation. For each baby who completed a testing condition, an average of 2.5 rolling movements occurred on the flat surface and 3.2, 1.9, 2.4, and 1.2 rolling movements occurred in the 0°, 10°, 18°, and 28° configurations, respectively. All six previously defined coordinated movements (Fig.2A-F) occurred on the flat surface and within the device configurations. However, in the device, a new coordinated movement (Fig.2O) occurred, where infants pressed their feet and shoulders into the device, resulting in hyperextension of the thoracic spine to achieve a roll. This new movement occurred more frequently as the seatback angle increased (Fig.2H). Even though fewer rolls were achieved in the 28° configuration, nearly half of them were the new movement. Proportions of coordinated movement types in the 10°, 18°, and 28° configurations were significantly different (p < 0.005) compared to the flat surface.

Conclusion: Infants use different movement patterns to achieve a roll based on the seatback angle, meaning that rolling milestone achievement on a flat surface does not directly translate to different mechanical environments.