Affiliations: [a] Rehabilitation Sciences Post-Graduation Program, Augusto Motta University Centre, Rio de Janeiro, Brazil | [b] School of Physiotherapy, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil | [c] Admiral Adalberto Nunes Physical Education Centre (Brazilian Navy), Rio de Janeiro, Brazil | [d] Post-Graduation Program in Medical Sciences, School of Medical Sciences, State University of Rio de Janeiro, Rio de Janeiro, Brazil
Correspondence:
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Corresponding author: Agnaldo José Lopes, Rua Araguaia, 1266, bloco 1/405, Freguesia, Jacarepaguá, 22745-271, Rio de Janeiro, Brasil. Tel.: +55 21 2576 2030; Fax: +55 21 2576 2030; E-mail: agnaldolopes.uerj@gmail.com.
Abstract: 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)D3) 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)D3. 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)D3 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)D3 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)D3 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.
Keywords: COPD, musculoskeletal dysfunction, respiratory function tests, quality of life, vitamin D
