Andre Nyberg, Didier Saey, Mickaël Martin, François Maltais
Heart and Lung Institute, University of Laval, G1V 4G5 Quebec, Canada. E-mail: andre.nyberg@criucpq.ulaval.ca
DOI: 10.2340/16501977-2354

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.

In people with chronic obstructive pulmonary disease (COPD), measuring the strength of the thigh muscle is highly recommended as it can provide valuable information about the clinical impact and the prognois of the disease. However, it is important that measurements are reliable, that is, that they are accurate, reproducible, and consistent from one testing occasion to another. In this study, people with COPD performed static maximal thigh muscle contractions against a fixed resistance at a knee angle of 90°. The results indicate that measuring maximal contractions performed by the patient themselves (volitional) or those achieved by stimulating the femoral nerve in the thigh (non- volitional), could reliably be used to assess thigh muscle strength in people with COPD, although the former technique seems to be most reliable.