Reliability of Quadriceps Femoris Muscle Strength Assessment Using a Portable Dynamometer and Protocol Tolerance in Patients With Chronic Obstructive Pulmonary Disease

Objective: This study aimed to evaluate the intrarater and interrater reliability of isometric quadriceps strength (IQS) using a portable dynamometer in individuals with chronic obstructive pulmonary disease (COPD) and to verify their tolerance to the protocol.

Methods: A cross-sectional reliability study was conducted with 50 individuals with stable COPD (34 men and 16 women; mean age = 70 years [SD = 8]). The main outcome measure was obtained using a portable dynamometer (Microfet 2) to assess IQS. Two masked raters performed 2 assessments in the dominant lower limb on 2 nonconsecutive days. The intraclass correlation coefficient (ICC) was used to verify the intrarater and interrater reliability and was considered excellent when >0.90, with a 5% significance level.

Results: Rater 1 and 2 intrarater reliability was as follows: ICC = 0.96 (95% CI = 0.94 to 0.98) and ICC = 0.97 (95% CI = 0.95 to 0.98), respectively. The interrater reliability was as follows: ICC = 0.96 (95% CI = 0.93 to 0.98). The minimum detectable difference was 4 to 5 peak isometric strength, in mean, for intrarater and interrater reliability. Not all patients presented relevant changes in physiological responses, dyspnea, and lower limb fatigue.

Conclusion: There was an excellent intrarater and interrater reliability for IQS, and the participants tolerated the protocol.

Impact: This tool can be used to assess quadriceps strength in clinical practice in patients with COPD.