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How do infants adapt to loading of the limb during the swing phase of stepping?
Tania Lam1, Claire Wolstenholme, Jaynie F Yang
1University Centre for Neuroscience and Department of Physical Therapy, University of Alberta, Edmonton, Alberta T6G 2G4, Canada.
Insights
Human infants adapt to leg loading during stepping by increasing muscle torques. Some infants show an "after-effect" when the load is removed, indicating enduring motor adaptations in their gait development.
Area of Science:
- Developmental neuroscience
- Motor control
- Human infant locomotion
Background:
- Human infants (<12 months) can adjust to brief sensory changes during stepping.
- Understanding how infants adapt to sustained sensory alterations is crucial for developmental motor studies.
Purpose of the Study:
- To investigate infant adaptation to a persistent sensory change (limb loading) during treadmill stepping.
- To analyze the immediate motor responses and potential after-effects following load removal.
Main Methods:
- Infants (3-11 months) had a weight (500-900g) attached to one leg during treadmill stepping.
- Leg motion was analyzed using a three-segment dynamic model to calculate joint torques.
- Responses to sudden weight detachment were recorded and analyzed.
Main Results:
- All infants increased hip and knee flexor muscle torques to compensate for the added load.
- 7 out of 22 infants displayed a high-stepping "after-effect" upon weight removal.
- This after-effect involved increased toe trajectory height and hip flexion, linked to higher hip flexor torque.
Conclusions:
- Infants demonstrate rapid muscle torque adjustments to adapt to sustained limb loading during stepping.
- The observed after-effect suggests enduring motor pattern adaptations in some infants, revealed by unexpected sensory unloading.
- These findings provide insights into the plasticity of infant motor control during gait development.
Abstract:
Previous results from this laboratory have shown that human infants (<12 mo old) respond appropriately to transient changes in sensory input during stepping. We examined how infants adapted to a more enduring change in sensory input by applying load to one limb during stepping. A small weight (500-900 g) was strapped around the lower leg of infants aged 3-11 mo. Stepping with the weight on was recorded on the treadmill for a period of 0.5-3 min. The weight was then quickly detached during stepping, and the immediate response to unexpected loss of the weight recorded. Three-segment dynamic analysis of leg motion was used to estimate hip, knee, and ankle torques during swing in the sagittal plane. All infants adapted to the additional load on the leg by immediately increasing the generation of hip and knee flexor muscle torques. When the weight was removed, 7 of the 22 infants tested exhibited an after-effect (high stepping) in the first step after removal of the weight. The after-effect was manifested as an increase in toe trajectory height and hip flexion and coincided with higher hip flexor muscle torque in early swing. In an additional series of control experiments using seven infants, after-effects were shown to be unrelated to a sudden change in cutaneous input with removal of the weight. The presence of an after-effect indicates that some infants made an enduring adaptation to their stepping pattern that is revealed with the unexpected removal of the weight.