Muscle activation and coordinated movements of infant rolling

Abstract

Rolling is a critical step of infant development, encouraging muscle coordination and enabling independent exploration. Understanding muscle activity during infant rolling movements on a flat surface is necessary to more fully characterize how the rolling milestone is achieved. The purpose of this study was to determine infants' muscle activation throughout roll initiation for six previously established coordinated movements. Thirty-eight healthy infants (age: 6.5 ± 0.7 months; 23M/15F) were enrolled in this IRB-approved in-vivo biomechanics study. Surface electromyography sensors recorded muscle utilization from the erector spinae, abdominal muscles, quadriceps, and hamstrings while infants rolled. Each rolling movement was categorized as one of six roll types, and the mean muscle activity was analyzed. All roll types required initial activation of all measured muscle groups. Movements featuring axial rotation of the torso relative to the pelvis required highly active erector spinae muscles. Movements featuring trunk and hip flexion required highly active abdominal muscles. Infants used distinct coordinated muscle activations to achieve the six different roll types on a flat surface. A foundational understanding of the different muscle activation patterns required during infant rolling will provide crucial insight into motor development. This study quantified muscle coordination required of infants to achieve rolling on a firm flat surface. Previous research indicates that the mechanical environment in which an infant is placed impacts muscle activity and body position during normal lying. Therefore, future work should explore if mechanical environments that differ from a flat and firm surface also influence these coordinated movements and muscle activations.

Keywords: Biomechanics; Motor development; Pediatrics; Product safety.

FIGURE 1:

Six previously established coordinated movements of rolling as defined by Kobayashi et. al. (2016), figures and captions adapted and reproduced with permission. Illustrated rolls are to the infants left. The limbs marked with an asterisk (*) are stationary throughout the roll, the dark gray limbs initiate the roll, and the light gray limbs follow after the roll has already been initiated.

FIGURE 2:

Experimental setup is shown on the left and EMG placement for the abdominal muscles (AB), quadriceps (QUAD), erector spinae (ES), and hamstrings (HAM) is shown on the right. The ES sensors were placed mid back on either side of the spine. The QUAD sensors were placed midway between the knee and the anterior superior iliac spine aligned with the femur bone. The HAM sensors were placed directly behind the QUAD sensors on the posterior side of the leg. Finally, the AB sensors were placed approximately two finger widths apart just above the belly button. EMG was also collected from the cervical paraspinals, gluteus maximus, and triceps brachii muscles. However, these muscle groups were not discussed as significant contributions were not found both in this study and through previous research (Kobayashi et al., 2021; Wang et al., 2020). A kinematic data set was also collected but was outside of the scope of analysis for this study.

FIGURE 3:

Percentage of total rolling movements completed for each coordinated movement with included mean age

FIGURE 4:

Top graph represents raw EMG data for the left quadricep while the bottom graph shows the filtered EMG data used for analysis for all muscle groups. Each graph compares a resting period and a single rolling movement (coordinated movement F) of a single trial.

FIGURE 5:

Mean muscle activation throughout the rolling movement for each of the six different coordinated movements (A-F). Each muscle group is represented as a percentage of the maximum mean muscle activation. Regions of green represent a low muscle activation, yellow is moderate, and red is a region of high muscle activation. Infant drawings adapted from Kobayashi, et al. (2016) and reproduced with permission.