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Despite its clinical relevance, there is no consensus on how to measure quadriceps muscle endurance in people with COPD. Moreover, the reliability of available measurement strategies are only partly known.

Aim: To determine test-retest reliability and feasibility of isokinetic, isometric and isotonic protocols to assess quadriceps muscle endurance in people with COPD.

Method: Fifty nine participants (FEV1 of predicted 55±18%, age 67±8 years) were included and tested in an interday multicentre test-retest design with test occasions separated by 5-9 days. Quadriceps muscle endurance was assessed using isokinetic, isometric and isotonic knee extension protocols controlled by a computerized dynamometer. Relative reliability was determined by intra-class correlation coefficient (ICC)( two-way mixed effects, absolute agreement, single measurement) and absolute reliability by standard error of measurement (SEM).

Result: Isokinetic measurements demonstrated very high relative reliability (ICC: [95% confidence interval] 0.97 [0.94-0.99]), and isometric and isotonic demonstrated high relative reliability (0.89 [0.79-0.94], and 0.89 [0.82-0.94], respectively). Mean values across test-retest occasions were 2122 joules, 49 seconds, and 29 repetitions, for isokinetic, isometric and isotonic measurements, respectively. Corresponding SEM values were 150 joules, 7 seconds, and 5 repetitions. All three measurement strategies were feasible with an average time consumption of less than 10 minutes and no major adverse events.

Conclusion: The results indicate that isokinetic, isotonic and isometric measurements of quadriceps muscle endurance are reliable and feasible in people with COPD.