Do Inclined Sleeping Surfaces Impact Infants’ Muscle Activity and Movement?: A Safe Sleep Product Design Perspective

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The design of inclined sleep products may be associated with an increased risk of suffocation when an infant finds themselves prone in the product. It is important to understand how different inclined sleep surface angles impact infants’ muscle activity when considering a safe sleep environment. The purpose of this study was to assess muscle activity of healthy infants when they lie supine and prone on different inclined crib mattress surfaces (0° vs. 10° vs. 20°). Fifteen healthy infants were recruited for this study. Surface EMG was recorded from cervical paraspinal, abdominal, lumbar erector spinae, and triceps muscles for 60 s during supine and prone positioning. Repeated measures ANOVAs and Bonferroni post-hoc adjustments were performed to test the effect of incline angles. Paired t-tests were performed to test the effect of position (supine vs. prone). During prone lying, abdominal muscle activity increased by 33% and 71% for 10° and 20° compared to 0°, while erector spinae and triceps muscle activity decreased for 20° compared to 0°. Lumbar erector spinae and cervical paraspinal muscle activity increased by 185% and 283% for prone compared to supine lying. During prone positioning, the 20° inclined surface resulted in significantly higher muscle activity of the trunk core muscles (abdominals), which may exacerbate fatigue and contribute to suffocation if an infant cannot self-correct to the supine position. Compared to supine positioning, prone lying requires higher musculoskeletal effort to maintain a safe posture to prevent suffocation, and babies likely fatigue faster when lying prone.