BACKGROUND:

There is a growing interest in identifying markers of pulmonary function that are predictive of peripheral muscle dysfunction in chronic obstructive pulmonary disease (COPD); however, studies of this relationship have yielded contradictory results in the literature.

OBJECTIVES:

To evaluate the strength and endurance of the quadriceps and hamstring muscles according to gender and to evaluate the associations between lower limb muscle function and lung function, health-related quality of life (HRQoL) and 25-hydroxivitamin D3 (25(OH)D 3 ) levels in patients with COPD.

METHODS:

Forty-two patients with COPD and 42 matched healthy controls underwent knee isokinetic dynamometry at 75 and 240 ∘ /s as well as isometric handgrip strength testing. All patients underwent pulmonary function tests and measurement of 25(OH)D 3 . HRQoL was evaluated using the COPD Assessment Test (CAT), the 36-Item Short-Form Health Survey (SF-36) and the Saint George’s Respiratory Questionnaire (SGRQ).

RESULTS:

Most isokinetic parameters showed differences between males and females as well as between COPD patients and controls; the greatest differences were observed among females with COPD and their matched controls. The strongest correlations were observed between the isokinetic parameters and the SF-36 physical component summary (PCS) and SGRQ and pulmonary function variables, especially at the higher velocity. At this velocity, the agonist/antagonist ratio was positively correlated with the SF-36 PCS (r = 0.65), 25(OH)D 3 levels (r = 0.76) and forced expiratory volume in one second (r = 0.65) and was negatively correlated with the CAT (r = - 0.53) and the SGRQ (r = - 0.64) ( P < 0.001 for all correlations). The associations between the isokinetic parameters and 25(OH)D 3 levels were stronger when endurance was tested.

CONCLUSIONS:

Patients with COPD show a reduction in both strength and endurance, especially in females. The relationships between muscle function, lung function, HRQoL and 25(OH)D 3 levels are most striking when endurance and hamstring/quadriceps muscle balance are tested. In COPD, forced expiratory volume in one second is the strongest marker of lung function that predicts muscle dysfunction.