How do babies roll? Identifying the coordinated movements of infant rolling through video compared to laboratory techniques

Abstract

Background: Rolling is an important developmental milestone for infants where identifying the coordinated movement patterns could facilitate the early identification of motor development delays. Current methods for identifying coordinated movements of rolling are limited to a laboratory setting and not feasible for clinicians.

Objective: To develop video-based methods in which six coordinated movements, previously defined through motion capture, can be identified through video alone.

Methods: Forty-five videos of sixteen healthy infants achieving a roll were used to develop the video-based methodology and twenty-four videos had corresponding motion capture data used for validation. Four raters comprised of researchers and a clinician identified rolling coordination using the new video-based methods. A Fleiss' Kappa statistical test determined the inter- and intra-rater reliability of agreement for the new methodology and compared it to motion capture.

Results: The comparison of the motion capture and video-based methods resulted in substantial agreement. The video-based methods inter- and intra-rater reliability were substantial and almost perfect, respectively.

Conclusions: We developed reliable methodology to accurately identify the coordinated movements of infant rolling using only 2D video. This methodology will allow researchers to reliably define coordinated movements of infants through video alone and may assist clinicians in identifying possible motor development delays and disorders.

Keywords: Motor development; biomechanics; experimental design; kinematics; milestones.

Fig. 1.

Six previously established coordinated movements of rolling showing the sequence throughout the movement [8]. The limbs are codified as ipsilateral arm (IA) and leg (IL) and contralateral arm (CA) and leg (CL) in the direction of the roll. Illustrated rolls are to the infant’s 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. Figures and captions adapted and reproduced with permission.

Fig. 2.

(A) Experimental setup showing retroreflective marker placement and the pulse oximeter (SpO₂ monitor) used to monitor safety. Electromyography sensors wrapped in self-adherent bandage were also used in this experimental setup but were outside the scope of this study. (B) Retroreflective marker placement used for data analysis where 3-marker rigid body clusters (6.5 mm markers) were placed on the torso and both feet and 9 mm individual markers were placed on the backs of both hands.

Fig. 3.

Time series plots showing example limb coordination speeds for movements B (Right) and C (Left) for the first 25% of the rolling movement. The blue line represents the contralateral arm (CA), the orange line represents the ipsilateral arm (IA), the yellow line represents the contralateral leg (CL), and the purple line represents the ipsilateral leg (IL). For coordinated movement B (Right) the CA initiates the rolling movement. For coordinated movement C (Left) the CA, CL, and IL work together to initiate the rolling movement.

Fig. 4.

Flow-chart used to guide the identification of the six previously defined coordinated movements based on the number of stationary limbs and the coordination of the moving limbs.