Test-re-test Reliability of Quadriceps Muscle Strength Measures in People with More Severe Chronic Obstructive Pulmonary Disease

Objective: To investigate the interday test-retest reliability of volitional and non-volitional measurements of isometric quadriceps strength using a strain-gauge in people with severe to very severe chronic obstructive pulmonary disease.

Design: Cross-sectional study. Volitional quadriceps measurements consisted of isometric maximal voluntary contractions. Non-volitional measurements were obtained during magnetic potentiated twitch stimulations of the femoral nerve.

Setting: Research centre laboratory.

Participants: Twenty-four individuals with severe to very severe chronic obstructive pulmonary disease (percentage of predicted forced expiratory volume in 1 s, 37% predicted).

Results: Maximal voluntary contractions and potentiated twitch stimulations measures demonstrated excellent interday test-retest relative reliability (ICC 0.97 and 0.80, respectively), while absolute reliability measures were different between techniques (SEM 1.4 kg, CV 3.2%, MDC 3.9 kg vs SEM 1.5 kg, CV 12.2%, MDC 4.2 kg for maximal voluntary contractions and potentiated twitch stimulations, respectively).

Conclusion: The results supports that maximal voluntary contraction and potentiated twitch stimulation measurements of isometric quadriceps strength are reliable in people with severe to very severe chronic obstructive pulmonary disease as evident excellent relative reliability using both techniques, although the former technique appears to have better absolute reliability.