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Electromyographic study of newborn stepping in neonates and young infants
T Okamoto1, K Okamoto, P D Andrew
1Department of Liberal Arts, Kansai Medical University, Osaka, Japan.
Insights
Newborn leg muscle activity transitions from excessive coactivation to reciprocal patterns within four months. These changes in neonatal stepping reflect developing balance, postural control, and strength.
Area of Science:
- Developmental neuroscience
- Motor control
- Pediatric physical therapy
Background:
- Neonatal stepping is an innate reflex crucial for early motor development.
- Understanding the evolution of leg muscle function during stepping provides insights into motor control maturation.
Purpose of the Study:
- To investigate developmental changes in leg muscle functional mechanisms during the first four months of human infant stepping.
- To analyze the transition from neonatal to young infant stepping patterns.
Main Methods:
- Electromyography (EMG) was used to record leg muscle activity in ten normal neonates.
- Analysis focused on muscle activation patterns, specifically coactivation and reciprocal firing, during the stance and swing phases of stepping.
Main Results:
- Neonatal stepping (first month) exhibited excessive coactivation of antagonist muscles, particularly during the stance phase.
- After the first month, stepping patterns shifted towards reciprocal muscle activation, though excessive activity and postural adjustments persisted.
- Leg extensor activity, associated with a parachute reaction before floor contact, emerged between one and three months of age.
Conclusions:
- Gradual changes in leg muscle activity during stepping are driven by the maturation of balance and postural control systems.
- Developing strength further modulates the neonatal stepping reflex, leading to more mature locomotion patterns.
- These findings highlight the dynamic interplay between neural development and motor execution in early infancy.
Abstract:
The purpose of this study was to examine the developmental changes in the functional mechanisms of leg muscles in newborn stepping over the first four months in ten normal neonates. Neonatal stepping in the first month showed excessive coactivation, that is, co-contraction patterns of mutual antagonists appeared especially during stance phase. The discharge patterns of co-contraction in neonatal stepping began to change to reciprocal patterns in young infant stepping (after the first month), but excessive muscular activities associated with a slightly squatted posture and forward lean still remained. Strong muscle activities of leg extensors due to a parachute reaction of the legs before floor contact, not seen in the neonatal period, began to appear in the young infant period from one month of age to three months. We suggest that these gradual changes of leg muscular activity in newborn stepping are evoked by development of balance, postural control, and strength, thereby modulating the neonatal stepping reflex.