Strength-duration curve: intrarater and interrater reliability

Area of Science:

• Neuromuscular Physiology
• Biomedical Engineering

Background:

• The strength-duration (SD) curve is a key electrodiagnostic tool.
• Assessing the reliability of SD curve production is crucial for accurate clinical interpretation.

Purpose of the Study:

• To determine the intrarater and interrater reliability coefficients for producing the strength-duration curve.
• To evaluate the consistency of SD curve measurements in healthy subjects.

Main Methods:

• Tested the tibialis anterior muscle in 24 healthy men.
• Intrarater reliability assessed via test-retest by the same examiner (1-week interval).
• Interrater reliability assessed by two examiners testing the same subject within 1 hour.

Main Results:

• Interrater reliability coefficients ranged from r = .771 to .979 (mean r = .945), indicating high consistency (variance r² = .89).
• Intrarater reliability coefficients ranged from r = .394 to .850 (mean r = .541), indicating lower consistency (variance r² = .29).
• Both mean coefficients were statistically significant (p < .01).

Conclusions:

• Interrater measurements of the strength-duration curve demonstrate high reliability.
• Intrarater measurements show lower reliability, potentially due to physiological variations in subjects.
• Normalization of strength-duration curves may be necessary to enhance measurement consistency.