title: Quadriceps strength and endurance in fibrotic idiopathic interstitial pneumonia.
abstract: OBJECTIVE
  Quadriceps muscle dysfunction is an important contributor to exercise limitation in chronic obstructive pulmonary disease, but little is known about skeletal muscle function and its impact on exercise capacity in patients with fibrotic idiopathic interstitial pneumonia (IIP). The aim of the study was to compare quadriceps strength and endurance in patients with fibrotic IIP and healthy controls, and relate it to exercise capacity.
  
  
  METHODS
  Quadriceps strength and endurance, as well as respiratory muscle strength, and 6-min walk distance were compared among 25 patients with fibrotic IIP, forced vital capacity mean (standard deviation) 78.7 (14.0) %predicted, carbon monoxide transfer factor 40.3 (10.9) %predicted and 33 age-matched healthy controls using non-volitional measures. Quadriceps strength was assessed using magnetic femoral nerve stimulation (quadriceps twitch force), and endurance using the decay in force in response to repetitive magnetic stimulation of the quadriceps over 5 min.
  
  
  RESULTS
  Both groups had comparable anthropometrics, gender proportion and respiratory muscle strength. Patients were significantly weaker than controls; quadriceps twitch force 10.1 (3.0) kg versus 8.0 (2.4) kg (P = 0.013). Quadriceps force in response to repetitive magnetic stimulation declined significantly more rapidly in patients during the endurance protocol (P < 0.001). In controls, there was a significant relationship between 6-min walk distance and quadriceps twitch force (r 0.40, P = 0.038), and quadriceps endurance (r 0.59, P = 0.016). In patients, only PaO2 and inspiratory muscle strength were retained as independent correlates of 6-min walk distance (r(2)  = 0.3 P = 0.022).
  
  
  CONCLUSIONS
  Quadriceps strength and endurance are reduced in patients with fibrotic IIP compared with healthy controls, but are less tightly correlated with exercise performance.
authors.affiliation: Hospital Clínico, Universidad de Chile, Santiago, Chile; National Institute for Health Research Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust and Imperial College, London, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Mendoza
authors.forename: Athena
authors.initials: A
authors.lastname: Gogali
authors.forename: Dinesh
authors.initials: D
authors.lastname: Shrikrishna
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cavada
authors.forename: Samuel V
authors.initials: SV
authors.lastname: Kemp
authors.forename: Samantha A
authors.initials: SA
authors.lastname: Natanek
authors.forename: Abigail S
authors.initials: AS
authors.lastname: Jackson
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
authors.forename: Athol U
authors.initials: AU
authors.lastname: Wells
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hopkinson
mesh_terms: D005080:Exercise Test; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D054988:Idiopathic Interstitial Pneumonias / Q000150:complications / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018908:Muscle Weakness / Q000209:etiology / Q000503:physiopathology*; D010807:Physical Endurance / Q000502:physiology*; D011379:Prognosis; D011446:Prospective Studies; D011658:Pulmonary Fibrosis / Q000150:complications / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000503:physiopathology*; D014797:Vital Capacity
keywords: exercise; interstitial lung disease; magnetic stimulation; muscle; pulmonary fibrosis