Reliability and performance-dependent variations of muscle function variables during isometric knee extension

Area of Science:

• Neuromuscular Physiology
• Sports Science
• Biomechanical Analysis

Background:

• Standardized methods for analyzing knee extensor neuromuscular function are common but lack test-retest reliability studies.
• Performance-dependent variations in muscle function and the interpretation of changes in measured variables remain unclear.

Purpose of the Study:

• To investigate performance-dependent variations in knee extensor muscle function during isometric contractions.
• To examine the test-retest reliability of measurement methods for key neuromuscular variables.

Main Methods:

• Sports students underwent three test sessions to assess test-retest reliability.
• Highly skilled athletes, sports students, and untrained subjects were compared for performance variations.
• Variables analyzed included maximal voluntary contraction (MVC), voluntary activation (VA), absolute muscle reaction time (AR), muscle endurance (ME), and EMG frequency analysis (MF) of vastus lateralis, vastus medialis, and rectus femoris.

Main Results:

• High test-retest reliability (ICC > 0.87) was observed for MVC, VA, and ME.
• Absolute muscle reaction time (AR) showed low to moderate reliability, while EMG frequency analysis (MF) demonstrated low reliability.
• Significant differences in nearly all analyzed variables (except VA) were found between trained (athletes, sports students) and untrained subjects.

Conclusions:

• MVC, VA, and ME are reliable measures for assessing isometric knee extensor function.
• Trained individuals exhibit distinct neuromuscular function profiles compared to untrained individuals.
• Further research is needed to improve the reliability of AR and MF measurements in this context.