Difference in the Motor Unit Firing Behavior During Submaximal Isometric Ramp Contraction Between Healthy Children...

Area of Science:

• Neuromuscular Physiology
• Developmental Neuroscience
• Motor Control

Background:

• Motor unit (MU) firing strategies during force production differ between children and adults due to nervous system maturation.
• Neural modulation of MU firing during submaximal contractions is not well understood.

Purpose of the Study:

• To investigate differences in MU firing behavior between children and young adults during isometric ramp contractions.
• To compare motor unit firing rates (FRs) and changes in FR (ΔMU FR) relative to recruitment thresholds (RTs) and force levels.

Main Methods:

• High-density surface electromyography recorded from the vastus lateralis during isometric knee extension.
• Data from 18 children (6-12 years) and 18 adults performing MVCs and submaximal ramp contractions.
• Individual MU firing was identified through decomposition, with analysis based on RTs.

Main Results:

• Children showed significantly higher MU FRs than adults across most RT groups and force levels.
• ΔMU FR was higher in children only in the initial 10%-20% MVC for low-threshold MUs.
• ΔMU FR was lower in children for higher-threshold MUs at higher force levels.

Conclusions:

• Higher MU FRs in children may compensate for immature muscle contractile properties, facilitating force generation.
• Distinct neural control strategies in children, including high initial firing rates and subsequent saturation, suggest ongoing spinal motor control maturation.
• Findings offer insights for pediatric neuromuscular disorder assessment and rehabilitation program design.