Reliability and validity of isometric knee extensor strength test with hand-held dynamometer depending on its...

Area of Science:

• Biomechanics
• Musculoskeletal assessment
• Rehabilitation technology

Background:

• Accurate measurement of isometric knee extensor strength is crucial for assessing muscle function and guiding rehabilitation.
• Hand-held dynamometers (HHDs) offer a portable alternative to isokinetic dynamometers, but their measurement reliability and validity are debated.
• The impact of device fixation on HHD performance in strength testing requires clarification.

Purpose of the Study:

• To evaluate the reliability and validity of a fixed versus non-fixed hand-held dynamometer (HHD) for measuring isometric knee extensor strength.
• To compare HHD measurements against a gold-standard isokinetic dynamometer.

Main Methods:

• Twenty-seven healthy females performed isometric knee extensions using an isokinetic dynamometer, a non-fixed HHD, and a fixed HHD (secured with Velcro).
• Measurements were taken in both seated and supine positions with the knee fixed at 35°.
• Peak torque values from three repetitions were analyzed for reliability and validity.

Main Results:

• The fixed HHD demonstrated significantly higher validity and reliability compared to the non-fixed HHD when correlated with isokinetic dynamometer results.
• Pearson correlation coefficients were significant for the fixed HHD (r=0.473-0.806) but largely non-significant for the non-fixed HHD.
• Both methods showed excellent inter-rater reliability, with the fixed HHD exhibiting slightly higher intraclass correlation coefficients (0.952-0.984 vs. 0.940-0.963).

Conclusions:

• Fixating the hand-held dynamometer during isometric knee extensor strength testing, particularly in the supine position, enhances measurement reliability and validity.
• This finding supports the use of a fixed HHD for more accurate quadriceps strength assessments in clinical and research settings.