Fixed Handheld Dynamometry Provides Reliable and Valid Values for Quadriceps Isometric Strength in People With Chronic Obstructive Pulmonary Disease: A Multicenter Study

Background. Quadriceps weakness is associated with poor clinical outcomes in chronic obstructive pulmonary disease (COPD). However, quadriceps isometric strength assessment has not been routinely adopted in clinical practice because of the lack of homogeneity in the devices and protocols and the lack of reliability studies. Objective. The objectives of this study were to determine the test-retest reliability and the criterion validity of a commercially available handheld dynamometer for evaluating the quadriceps isometric maximal voluntary contraction (iMVC(quad)) using a standardized protocol and to investigate the relationship between iMVC(quad) and functional capacity in people with COPD. Design. This was a prospective, observational, multicenter trial. Methods. Participants with mild to severe COPD from 4 Canadian sites were tested on 2 separate days. Five iMVC(quad) measurements were obtained following a standardized procedure with a fixed handheld dynamometer (iMVC(quad-HHD)), and then 5 iMVC(quad) measurements were obtained with a computerized dynamometer (iMVC(quad-CD); the gold standard). Functional capacity was assessed with the Short Physical Performance Battery. Intraclass correlation coefficients, standard errors of measurement, Bland-Altman plots, and Spearman correlation coefficients were used for analyses. Results. Sixty-five participants (mean age = 69 years [SD = 8]; forced expiratory volume in 1 second = 48% of predicted value [SD = 21]) completed the study. The mean iMVC(quad-HHD) values on visits 1 and 2 were 102.7 (SD = 51.6) and 105.6 (SD = 58.8) N.m, respectively; the standard error of measurement was 11.4 N.m. The between-visits intra-class correlation coefficient for iMVC(quad-HHD) was 0.95 (95% confidence interval = 0.92-0.97), with a mean bias of 2.0 (Bland-Altman plot). There was a strong correlation between iMVC(quad-HHD) and iMVC(quad-CD) (Spearman correlation coefficient = 0.86). There was no correlation between iMVC(quad-HHD) and Short Physical Performance Battery total score. Limitations. Participants had stable COPD with few comorbidities and were more physically active than the general population of people with COPD; results might not be applicable to patients with acute exacerbations of the disease or more comorbidities. Assessment order between handheld and computerized dynamometers has not been randomized, but analyses did not highlight any systematic bias or learning effect. Conclusions. Quadriceps strength assessment can be implemented in a reliable and valid way in people with COPD using a fixed handheld dynamometer and standardized procedure. This protocol should be established in clinical practice to facilitate the assessment of muscle strength in people with COPD.