Accuracy, reproducibility, and variability of hand-held dynamometry in motor neuron disease

Area of Science:

• Neurology
• Rehabilitation Medicine
• Biomedical Engineering

Background:

• Hand-held dynamometry (HHD) is widely used for muscle strength assessment.
• Variability and reproducibility of HHD readings are critical for clinical trials and patient monitoring.
• Rater experience and the number of raters can influence measurement outcomes.

Purpose of the Study:

• To evaluate the impact of rater experience and the number of raters on the accuracy, reproducibility, and variability of HHD measurements.
• To assess the reliability of HHD in patients with motor neuron disease (MND).
• To determine the effectiveness of a composite score in improving measurement precision.

Main Methods:

• A spring-loaded device was used to calibrate HHD readings.
• Three raters with varying experience assessed muscle strength in 19 patients with MND.
• Muscle force was measured in nine muscle groups over six days and compared to normal controls.
• A composite score combining normalized readings from eight limb muscles was analyzed.

Main Results:

• Overall accuracy improved with rater experience, but reproducibility and variability did not.
• Readings from three raters showed 53% greater variability than single-rater readings.
• The experienced rater demonstrated good reproducibility (13.2% mean difference, 2.17 kg-force repeatability coefficient) over six days.
• Rater contributed 37% to total variability; a composite score improved mean % difference to 6.7% and mean CV to 5.8%.

Conclusions:

• Single-rater HHD measurements offer good reproducibility and variability, comparable to fixed devices.
• Using multiple raters in longitudinal studies significantly increases measurement variability.
• Composite scores can enhance the precision of HHD measurements, particularly in clinical trials.