Optimization of modularity during development to simplify walking control across multiple steps

Area of Science:

• Motor Control
• Developmental Neuroscience
• Biomechanics

Background:

• Adult walking is characterized by modular control, minimizing the degrees of freedom regulated by the central nervous system (CNS).
• Toddler walking also appears modular but exhibits high stride-to-stride variability, with the interplay between variability and modularity unclear.

Purpose of the Study:

• To investigate the modular organization of walking in toddlers compared to adults.
• To determine if motor variability in toddlers during walking is centrally or peripherally regulated.

Main Methods:

• Electromyographic (EMG) activity of 10 lower limb muscles was recorded in 12 adults and 12 toddlers over 8 gait cycles.
• Non-negative matrix factorization (Space-by-Time Decomposition) was used to model modular control, comparing averaged and non-averaged data.
• Toddlers were tested walking independently and supported by an adult to assess the impact of reduced balance constraints.

Main Results:

• Toddlers displayed significantly higher stride-to-stride variability than adults in both independent and supported walking conditions.
• More modules were required to account for toddler variability, with module activations being less consistent across strides compared to adults.
• This increased variability and modularity persisted in toddlers even when balance constraints were reduced.

Conclusions:

• The modular control of locomotion evolves significantly from toddlerhood to adulthood through practice and development.
• Adults utilize a more parsimonious modular strategy for walking compared to toddlers.
• Toddler variability, even with lowered balance constraints, suggests a role in motor exploration rather than solely corrective mechanisms.