Mechanical environment influences muscle activity during infant rolling.

An infant's musculoskeletal and motor development is largely affected by their environment. Understanding how different mechanical environments affect an infant's movements and muscle use is necessary to inform the juvenile products industry and reduce incidents involving inclined nursery products each year. The purpose of this study was to determine how the coordinated movements and corresponding muscle activation patterns are affected by different mechanical environments, specifically the back incline angle. Thirty-eight healthy infants (age: 6.5 ± 0.7 months; 23 M/15 F) were enrolled in this IRB-approved in-vivo biomechanics study. Surface electromyography sensors recorded muscle activity of the erector spinae, abdominal muscles, quadriceps, and hamstrings while infants rolled in five different mechanical environments: a flat surface and four device configurations representing a range of inclines infants are commonly exposed to. Coordinated movements were determined using video. In all configurations featuring an inclined seatback angle, infants experienced significantly higher erector spinae muscle activation and significantly lower abdominal muscle activation compared to the flat surface. Infants also exhibited a different coordinated movement featuring spinal extension and a pelvic thrust in the inclined device configurations that was not previously observed on the flat surface alone. Understanding how infants coordinate their movements and use their muscles during rolling in different inclined environments provides more insight into motor development and may inform the juvenile products industry. Many factors impact an infant's movements, therefore future work should explore how other environmental interactions influence an infant's movements and muscle activation, particularly for rolling.

Muscle activation and coordinated movements of infant rolling.

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.

Validation of a custom spine biomechanics simulator: A case for standardization.

Mechanical testing machines used in cadaveric spine biomechanics research vary between labs. It is a necessary first step to understand the capabilities and limitations in any testing machine prior to publishing experimental data. In this study, a reproducible protocol that uses a synthetic spine was developed and used to quantify the inherent rotation error and the ability to apply loads in a single physiologic plane (pure-moment) of a custom spine biomechanics simulator. Rotation error was evaluated by comparing data collected by the test machine and the data collected by an optical motion capture system. Pure-moment loading was assessed by comparing the out-of-plane loads to the primary plane load. Using synthetic functional spine units previously shown to have mechanics similar to the cadaveric human spine, the simulator was evaluated using a dynamic test protocol reflective of its future use in the study of cadaveric spine specimens. Rotation errors inherent in the test machine were <0.25° compared to motion capture. Out of plane loads were <4.0% of the primary plane load, which confirmed pure-moment loading. The authors suggest that a standard validation protocol for biomechanical spine testing machines is needed for transparency and accurate field-wide data interpretation and comparison. We offer recommendations based on the reproducible use of a synthetic spinal specimen for consideration.