title: Association between peripheral muscle strength, exercise performance, and physical activity in daily life in patients with Chronic Obstructive Pulmonary Disease.
abstract: BACKGROUND
  Resistance training of peripheral muscles has been recommended in order to increase muscle strength in patients with Chronic Obstructive Pulmonary Disease (COPD). However, whether peripheral muscle strength is associated with exercise performance (EP) and physical activity in daily life (PADL) in these patients needs to be investigated. The aim of this study is to evaluate whether strength of the quadriceps muscle (QS) is associated with EP and daily PADL in patients with COPD.
  
  
  METHODS
  We studied patients with COPD (GOLD A-D) and measured maximal isometric strength of the left QS. PADL was measured for 7 days with a SenseWear-Pro® accelerometer. EP was quantified by the 6-minute walk distance (6MWD), the number of stands in the Sit-to-Stand Test (STST), and the handgrip-strength. Univariate and multivariate analyses were used to examine possible associations between QS, PADL and EP.
  
  
  RESULTS
  In 27 patients with COPD with a mean (SD) FEV1 of 37.6 (17.6)% predicted, QS was associated with 6MWD, STST, and handgrip-strength but not with PADL. Multiple linear regression analyses showed that QS was independently associated with the 6MWD (β = 0.42, 95% CI 0.09 to 0.84, p = 0.019), STST (β = 0.50, 95% CI 0.11 to 0.86, p = 0.014) and with handgrip-strength (β = 0.45, 95% CI 0.05 to 0.84, p = 0.038).
  
  
  CONCLUSIONS
  Peripheral muscle strength may be associated with exercise performance but not with physical activity in daily life. This may be due to the fact that EP tests evaluate patients' true abilities while PADL accelerometers may not.
authors.affiliation: Pulmonary Division, University Hospital of Zurich, Zurich, Switzerland ; Department of Physiotherapy, Zurich University of Applied Sciences, Winterthur, Switzerland ; Zurich University of Applied Sciences, School of Health Professions, Department of Physiotherapy, Technikumstrasse 71, 8401 Winterthur, Switzerland.
authors.forename: Anne-Kathrin
authors.initials: AK
authors.lastname: Rausch-Osthoff
authors.affiliation: Pulmonary Division, University Hospital of Zurich, Zurich, Switzerland ; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
authors.forename: Malcolm
authors.initials: M
authors.lastname: Kohler
authors.affiliation: Pulmonary Division, University Hospital of Zurich, Zurich, Switzerland.
authors.forename: Noriane A
authors.initials: NA
authors.lastname: Sievi
authors.affiliation: Pulmonary Division, University Hospital of Zurich, Zurich, Switzerland.
authors.forename: Christian F
authors.initials: CF
authors.lastname: Clarenbach
authors.affiliation: Pulmonary Division, University Hospital of Zurich, Zurich, Switzerland ; Department of Physiotherapy, Zurich University of Applied Sciences, Winterthur, Switzerland.
authors.forename: Arnoldus Jr
authors.initials: AJ
authors.lastname: van Gestel
keywords: Accelerometer; Handgrip-strength; Quadriceps strength; Sit-to-stand-test; Six-minute-walk-distance