Infant positioning impacts muscle activity: Implications for proper musculoskeletal and motor development

• In Event: 1-048 - Keep on carrying on: Effects of carrying on infant nutrition, motor development, and social interaction

Integrative Statement

Introduction
Western parents are bombarded by infant products that subject babies to very specific positions, yet little research has been done to understand the biomechanical impact of placing infants in common positions or devices. An excess of supine (back) lying has been linked to plagiocephaly (flattening of the skull) that often requires treatment with a helmet, and some believe a link can be made between excessive supine lying and scoliosis [Mau, 1981; McMaster, 1983]. Recently, relationships between muscle forces and proper spine and hip development were found in fetal chick and neonatal mouse models, leading to more questions regarding the role of active muscles in proper musculoskeletal development [Rolfe, 2017; Ford, 2017]. While it is known that prone positioning (tummy-time) is linked to extensor muscle development and motor-milestone achievements [Zachry, 2017; Jennings, 2005], many parents find tummy-time uncomfortable for their babies and therefore avoid it. It would be beneficial to understand if different positions or gear encourages or discourages infants to use their muscles in a similar way to tummy-time, yet no evidence-based research has been done to understand the musculoskeletal impact of positions or devices on infants. The purpose of this pilot study is to examine relationships between infant positioning and muscle activity using surface electromyography (EMG).

Hypothesis
Infants will exhibit differences in muscle activity depending on their position.

Study Population
Full-term healthy infants (2-6 months).

Methods
Fourteen healthy infants (4.3±1.6 months, 9 male) were enrolled in the IRB-approved study. Surface EMG recorded muscle activity of cervical paraspinals (neck), erector spinae (back), gluteus medius (buttocks), biceps femoris (hamstrings), quadriceps, and adductor muscle groups during five 30-second tasks: lying prone, lying supine, in a car seat, held in arms (Figure 1), and held in a babycarrier. Because tummy-time is known to promote muscle activity, EMG data was normalized to the prone task. Paired t-tests were used to compare mean EMG to the prone task (p<0.05).

Results and Discussion
Mean cervical paraspinal (neck) muscle activity was not different between the prone, in arms, and babycarrier conditions, but was over twice as much as the supine and car seat positions (p<0.01) (Figure 2). Infants exhibited significantly more erector spinae (back) muscle activity during prone lying compared to all other tasks, and twice as much compared to supine lying (p<0.01). By encouraging babies to use and strengthen their back and neck muscles, they may achieve head control earlier. Lower-extremity muscle activity showed similar trends with prone lying exhibiting the most muscle activity, over 3.5 times more than the car seat condition (p<0.01). This first look at the muscle activity of healthy infants in common positions supports: (1) the importance of tummy-time time for motor and musculoskeletal development of both the spine and the hips, (2) beneficial neck muscle activity while being held both in arms and in a babycarrier which may promote head-control development, and (3) significantly lower back, neck, and lower-extremity muscle activity while in a car seat which may delay or alter musculoskeletal development.

Authors

• Erin Mannen, University of Arkansas for Medical Sciences
  Presenting Author

• Akshay Krishnan, University of Arkansas for Medical Sciences
  Non-Presenting Author

• Stewart Tackett, University of Arkansas for Medical Sciences
  Non-Presenting Author

• Richard McCarthy, University of Arkansas for Medical Sciences
  Non-Presenting Author

• David Bumpass, University of Arkansas for Medical Sciences
  Non-Presenting Author