PC2134: Muscle Activation of Infant Rolling Movements on a Flat Surface

Background: Achieving a roll is an important developmental milestone and key motor skill for infants. To initiate and complete a roll, infants use whole-body, goal-oriented movements that take them from a supine to prone position (Richter 1989). Our previous study on the muscle activation of infants lying in inclined sleeper products concluded that these products may facilitate rolling (Wang 2020). However, a more thorough understanding of rolling on a flat surface is required to elucidate exactly how product design impacts an infant’s ability to roll. Infants use six different coordinated techniques for rolling movements (Kobayashi 2016), but no studies have explored how these movements relate to muscle activation. The purpose of this study is to characterize the muscle activation of infants rolling on a flat surface.

Methods: Twenty-four infants (6.7±0.7 months, 10F) participated in this IRB-approved study (126-MED20-005). The infants laid supine on a playmat for five minutes or until a roll was achieved. Surface electromyography sensors (Delsys, 2000Hz) recorded muscle activity from the erector spinae, hamstrings, abdominal muscles, and quadriceps. A GoPro camera recorded all trials to identify the coordinated movement type. A medical-grade pulse oximeter monitored the infants SpO2 levels to ensure safety (Fig.1). Using MATLAB, we filtered the electromyography signal (Siddicky 2020) and normalized it to a five-second resting period for seventy-two rolling movements, defined as a supine to lateral rotation necessary to complete a roll. We categorized data by muscle group and coordinated movement. We calculated the mean at each time point throughout the rolling movement and represented it as a percentage of the maximum mean muscle activation for that muscle group. A >50% threshold value represented periods of higher muscle activity (Howard 2017).

Results: All six previously defined coordinated movements were observed. For movement A (Fig.2A), all muscle groups are working at a higher muscle activation during the first half of the movement, indicating that infants engage all muscles to initiate the roll. For movements B (Fig.2B) and E (Fig.2E), the axial rotation is supported by the high erector spinae activation throughout the movement. For movements C (Fig.2C) and F (Fig.2F), the sagittal plane flexion used to achieve this roll type is facilitated by the high abdominal and quadriceps muscle activity. For movement D (Fig.2D), all muscle groups have high muscle activation for the second half of the movement indicating that infants must engage all muscles to complete the roll.

Conclusion: These results demonstrate a promising method to quantify the coordinated movements and muscle activation of infant rolls using a combination of video and electromyography. Future studies exploring how rolling changes with age are required to characterize infant rolling behaviors more robustly over development.