Error associated with antagonist muscle activity in isometric knee strength testing.

Area of Science:

• Biomechanics
• Human Movement Science
• Sports Medicine

Background:

• Accurate measurement of isometric strength is crucial for assessing muscle function and imbalances.
• Antagonist muscle co-activation can introduce measurement error in strength testing.
• Understanding sex-based differences in muscle strength and co-activation is important for clinical and performance applications.

Purpose of the Study:

• To quantify the measurement error from antagonist muscle activity during isometric knee strength testing.
• To compare this error between knee extension and knee flexion.
• To investigate sex differences in measurement error during knee strength testing.

Main Methods:

• Collected electromyography (EMG) and moment data from 22 participants during isometric knee strength tests.
• Developed subject-specific EMG-moment relationships using polynomial equations.
• Calculated antagonist moments and expressed them as a percentage of agonist moments to determine error.

Main Results:

• Antagonist activity contributed 11.0% error for quadriceps and 8.7% for hamstrings.
• Error was significantly higher in knee flexion (20.1%) compared to knee extension (4.5%).
• Females exhibited significantly greater error during knee flexor testing.

Conclusions:

• Antagonist muscle activity introduces minimal error in knee extensor strength testing but significant error in knee flexor testing.
• The strength disparity between quadriceps and hamstrings contributes to higher flexion error.
• Accounting for antagonist co-contraction did not significantly alter limb symmetry indices.