Validation of isometric quadriceps muscle strength testing and relationship with functional capacity in COPD

Abstract

Context: Clinical assessment of muscle strength in COPD is not routinely adopted for many reasons, including lack of standardized protocols and validation studies on simple clinical tools. Aims: To determine 1) test-retest reliability of isometric quadriceps maximal voluntary contractions (iMVC) with a fixed handheld dynamometer (iMVCHD); 2) its construct validity against computerized dynamometry (iMVCCD), and 3) relationships between iMVCHD and functional capacity. Methods: 65 patients with COPD (69±8 years old, FEV1 48±21% of predicted) were tested at 4 Canadian sites on 2 separate days. The iMVCHD was measured with the fixed dynamometer [Medup] and iMVCCD with the Biodex following standardized protocols. Functional capacity was assessed with the Short Physical Performance Battery (SPPB). Intra-class correlation coefficient (ICC2,1) and standard error of measurement (SEM) were used for reliability analyses. Construct validity and associations between iMVCHD and SPPB were analysed with Spearman correlations. Results: Mean peak values for iMVCHD and iMVCCD were, respectively, 102.7±51.6 and 105.4±45.8Nm (day 1) and 105.6±58.8 and 105.4±46.9Nm (day 2), with an ICC of 0.95 [95%CI 0.92-0.97] and a SEM of 17.7Nm for iMVCHD. Spearman’s correlation between devices was 0.88 (p Conclusion: Assessment of quadriceps iMVC using a fixed handheld dynamometer shows excellent reliability and good construct validity, which favors its clinical implementation in COPD. Factors other than isometric quadriceps muscle strength may contribute to functional capacity.