Effect of Knee Joint Angle and Contraction Intensity on Hamstrings Coactivation

Area of Science:

• Biomechanics
• Motor Control
• Gerontology

Background:

• Muscle coactivation, particularly antagonist coactivation, is crucial for joint stability and motor control.
• Understanding age-related changes in muscle activation patterns is important for injury prevention and rehabilitation.

Purpose of the Study:

• To investigate how knee joint angle and contraction intensity affect hamstring coactivation in young and older adults.
• To determine if age influences antagonist coactivation levels.

Main Methods:

• 25 young and 26 older adults performed isometric knee extensor contractions at 20%, 50%, and 80% maximal voluntary contraction at 90° and 60° knee flexion.
• Surface electromyography (EMG) of vastus lateralis and biceps femoris measured agonist and antagonist muscle activation.
• Subcutaneous adipose tissue thickness was measured using ultrasonography.

Main Results:

• Higher antagonist coactivation and agonist activation were observed at 90° knee flexion compared to 60° across all intensities.
• Older adults exhibited greater antagonist coactivation at 60° knee flexion than younger adults, even after accounting for subcutaneous adipose tissue.

Conclusions:

• Antagonist coactivation is significantly influenced by knee joint angle and contraction intensity.
• Subcutaneous adipose tissue may impact EMG-based coactivation measurements, potentially through cross-talk.
• Age-related differences in coactivation may have implications for knee joint stability and motor output regulation.