Body Weight Control Is a Key Element of Motor Control for Toddlers' Walking

Area of Science:

• Neuroscience
• Motor Control
• Developmental Biology

Background:

• Infants can exhibit stepping reflexes with substantial body weight support (70-80%).
• Gravity-related sensorimotor feedback is hypothesized to be crucial for independent walking development.
• Understanding how altered body weight affects early motor control is key to deciphering walking acquisition.

Purpose of the Study:

• To investigate the effects of varying body weight support on motor control in toddlers during initial independent walking.
• To compare motor control strategies between novice walkers and those with approximately six months of walking experience under different support conditions.

Main Methods:

• Electromyography (EMG) of 18-24 leg and back muscles and vertical ground reaction forces were recorded in 16 typically developing children.
• Children walked on a treadmill under four body weight support (BWS) conditions: none (<10%), low (10-35%), medium (35-55%), and high (55-95%).
• Muscle synergies and network analyses were performed to compare motor control across support levels and age groups.

Main Results:

• Muscle activity patterns in both groups could be characterized by four distinct muscle synergies.
• Mean muscle activity, particularly around foot strike, decreased with increasing body weight support.
• The 'first-steps' group exhibited altered temporal patterns in muscle synergies when BWS exceeded 35%, with a denser, more interconnected muscle network.

Conclusions:

• The ability to effectively utilize gravity-related information for motor control is not fully developed at the onset of independent walking.
• Reduced reliance on gravity cues due to body weight support reveals distinct neural control mechanisms for emerging motor skills.
• Sensitivity of specific muscle synergies to unloading suggests specialized neural pathways govern their activation and coordination during gait development.