Article Text
Abstract
Background: Based on previously reported changes in muscle metabolism that could increase susceptibility to fatigue, we speculated that patients with chronic obstructive pulmonary disease (COPD) have reduced quadriceps endurance and that this will be correlated with the proportion of type I muscle fibres and with the activity of oxidative enzymes.
Methods: The endurance of the quadriceps was evaluated during an isometric contraction in 29 patients with COPD (mean (SE) age 65 (1) years; forced expiratory volume in 1 second 37 (3)% predicted) and 18 healthy subjects of similar age. The electrical activity of the quadriceps was recorded during muscle contraction as an objective index of fatigue. The time at which the isometric contraction at 60% of maximal voluntary capacity could no longer be sustained was used to define time to fatigue (Tf). Needle biopsies of the quadriceps were performed in 16 subjects in both groups to evaluate possible relationships between Tf and markers of muscle oxidative metabolism (type I fibre proportion and citrate synthase activity).
Results: Tf was lower in patients with COPD than in controls (42 (3) v 80 (7) seconds; mean difference 38 seconds (95% CI 25 to 50), p<0.001). Subjects in both groups had evidence of electrical muscle fatigue at the end of the endurance test. In both groups significant correlations were found between Tf and the proportion of type I fibres and citrate synthase activity.
Conclusion: Isometric endurance of the quadriceps muscle is reduced in patients with COPD and the muscle oxidative profile is significantly correlated with muscle endurance.
- BMI, body mass index
- COPD, chronic obstructive pulmonary disease
- CS, citrate synthase
- FEV1, forced expiratory volume in 1 second
- FVC, forced vital capacity
- HADH, 3-hydroxyacyl CoA dehydrogenase
- HK, hexokinase
- LDH, lactate dehydrogenase
- MTCSA, mid thigh muscle cross sectional area
- MVC, maximal voluntary contraction
- MVC/MTCSA, ratio of maximal strength to mid thigh muscle cross sectional area
- Pao2, arterial oxygen tension
- Paco2, arterial carbon dioxide tension
- PFK, phosphofructokinase
- Sao2, arterial oxygen saturation
- Tf, time to fatigue
- TLC, total lung capacity
- Tlco, lung carbon monoxide transfer factor
- Vo2, oxygen consumption
- chronic obstructive pulmonary disease
- muscle
- endurance
Statistics from Altmetric.com
- BMI, body mass index
- COPD, chronic obstructive pulmonary disease
- CS, citrate synthase
- FEV1, forced expiratory volume in 1 second
- FVC, forced vital capacity
- HADH, 3-hydroxyacyl CoA dehydrogenase
- HK, hexokinase
- LDH, lactate dehydrogenase
- MTCSA, mid thigh muscle cross sectional area
- MVC, maximal voluntary contraction
- MVC/MTCSA, ratio of maximal strength to mid thigh muscle cross sectional area
- Pao2, arterial oxygen tension
- Paco2, arterial carbon dioxide tension
- PFK, phosphofructokinase
- Sao2, arterial oxygen saturation
- Tf, time to fatigue
- TLC, total lung capacity
- Tlco, lung carbon monoxide transfer factor
- Vo2, oxygen consumption
Footnotes
-
This study was supported in part by an educational research grant form Bayer Corporation. FM is a research scholar of the Fonds de Recherche en Santé du Québec.
-
This work was presented in part at the annual meeting of the American College of Sports Medicine, St-Louis, Missouri, June 2002.