title: Skeletal muscle power and fatigue at the tolerable limit of ramp-incremental exercise in COPD.
abstract: Muscle fatigue (a reduced power for a given activation) is common following exercise in chronic obstructive pulmonary disease (COPD). Whether muscle fatigue, and reduced maximal voluntary locomotor power, are sufficient to limit whole body exercise in COPD is unknown. We hypothesized in COPD: 1) exercise is terminated with a locomotor muscle power reserve; 2) reduction in maximal locomotor power is related to ventilatory limitation; and 3) muscle fatigue at intolerance is less than age-matched controls. We used a rapid switch from hyperbolic to isokinetic cycling to measure the decline in peak isokinetic power at the limit of incremental exercise ("performance fatigue") in 13 COPD patients (FEV149 ± 17%pred) and 12 controls. By establishing the baseline relationship between muscle activity and isokinetic power, we apportioned performance fatigue into the reduction in muscle activation and muscle fatigue. Peak isokinetic power at intolerance was ~130% of peak incremental power in controls (274 ± 73 vs. 212 ± 84 W, P < 0.05), but ~260% in COPD patients (187 ± 141 vs. 72 ± 34 W, P < 0.05), greater than controls (P < 0.05). Muscle fatigue as a fraction of baseline peak isokinetic power was not different in COPD patients vs. controls (0.11 ± 0.20 vs. 0.19 ± 0.11). Baseline to intolerance, the median frequency of maximal isokinetic muscle activity, was unchanged in COPD patients but reduced in controls (+4.3 ± 11.6 vs. -5.5 ± 7.6%, P < 0.05). Performance fatigue as a fraction of peak incremental power was greater in COPD vs. controls and related to resting (FEV1/FVC) and peak exercise (V̇E/maximal voluntary ventilation) pulmonary function (r2= 0.47 and 0.55, P < 0.05). COPD patients are more fatigable than controls, but this fatigue is insufficient to constrain locomotor power and define exercise intolerance.
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California.|School of Exercise & Nutritional Sciences, San Diego State University, San Diego, California.
authors.forename: Daniel T
authors.identifier: 0000-0002-2175-3445
authors.initials: DT
authors.lastname: Cannon
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California.|Department of Pulmonology, Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil; and.
authors.forename: Ana Claudia
authors.initials: AC
authors.lastname: Coelho
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California.
authors.forename: Robert
authors.initials: R
authors.lastname: Cao
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California.
authors.forename: Andrew
authors.initials: A
authors.lastname: Cheng
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California.
authors.forename: Janos
authors.initials: J
authors.lastname: Porszasz
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California.
authors.forename: Richard
authors.initials: R
authors.lastname: Casaburi
authors.affiliation: Division of Respiratory & Critical Care Physiology & Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California; hrossiter@ucla.edu.|Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom.
authors.forename: Harry B
authors.identifier: 0000-0002-7884-0726
authors.initials: HB
authors.lastname: Rossiter
mesh_terms: D000368:Aged; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D008124:Locomotion / Q000502:physiology; D008168:Lung / Q000503:physiopathology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012146:Rest / Q000502:physiology
keywords: chronic obstructive pulmonary disease; exercise intolerance; isokinetic