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ABSTRACT
Background and Purpose: A new pull-type dynamometer, the EasyForce®, may offer clinical advantages for measuring strength. The purpose of the current study was to assess the intra-rater reliability of the EasyForce® and its concurrent validity compared to the Lafayette Manual Muscle Tester in healthy individuals. Methods: Maximal voluntary isometric contraction was tested using the Lafayette Manual Muscle Tester and the EasyForce® to explore the association between the two instruments. Measurements of the shoulder girdle and knee were performed on healthy, active individuals recruited from the undergraduate and graduate student population on two separate days, with 48-72 hours between sessions and at the same time of day for each participant. Results: Thirty participants, age 29.97± 3.25 years, were enrolled in the study. Intraclass correlation coefficients for the Easy-Force® ranged from 0.87-0.98 for the shoulder and 0.80-0.81 for the knee. Assessment of concurrent validity demonstrated strong correlations between the EasyForce® and Lafayette dynamometers for all measurements in both sessions, which were statistically significant (τb = 0.45 to 0.78, p<.001). Wilcoxon signed-rank tests showed statistically significant differences between devices during both sessions (p<0.001 to p=0.02). Clinical Relevance: Based on the results of this study, clinicians should consistently use the same dynamometer, regardless of type, across treatment sessions to measure strength changes. Conclusion: The EasyForce® is a reliable and valid tool to measure strength of the upper and lower extremities.
Key Words: force production, Lafayette Manual Muscle Tester, strength assessment, muscle testing
INTRODUCTION
Manual muscle testing (MMT) is commonly implemented in clinical practice to assess strength, by examining volitional activity throughout an arc of motion.1,2 Manual muscle testing is graded on a 0-5 scale, with higher grades representing increased strength.2 A previous literature review concluded that MMT is clinically useful during the examination process, but further research is needed to validate the results.1 Given the questionable reliability of MMT grades above 3/5, other methods of strength assessment have frequently been implemented in clinical practice to provide a more precise level of measurement that is sensitive to small changes in strength.3,4 This is particularly important when making decisions regarding return to play, during assessment of side to side strength symmetry for reducing risk of re-injury.5-8
Handheld dynamometry (HHD) provides another option for strength assessment at a significantly lower...