title: Exercise intolerance at high altitude (5050 m): critical power and W'.
abstract: The relationship between work rate (WR) and its tolerable duration (t(LIM)) has not been investigated at high altitude (HA). At HA (5050 m) and at sea level (SL), six subjects therefore performed symptom-limited cycle-ergometry: an incremental test (IET) and three constant-WR tests (% of IET WR(max), HA and SL respectively: WR(1) 70±8%, 74±7%; WR(2) 86±14%, 88±10%; WR(3) 105±13%, 104±9%). The power asymptote (CP) and curvature constant (W') of the hyperbolic WR-t(LIM) relationship were reduced at HA compared to SL (CP: 81±21 vs. 123±38 W; W': 7.2±2.9 vs. 13.1±4.3 kJ). HA breathing reserve (estimated maximum voluntary ventilation minus end-exercise ventilation) was also compromised (WR(1): 25±25 vs. 50±18 l min(-1); WR(2): 4±23 vs. 38±23 l min(-1); WR(3): -3±18 vs. 32±24 l min(-1)) with near-maximal dyspnea levels (Borg) (WR(1): 7.2±1.2 vs. 4.8±1.3; WR(2): 8.8±0.8 vs. 5.3±1.2; WR(3): 9.3±1.0 vs. 5.3±1.5). The CP reduction is consistent with a reduced O(2) availability; that of W' with reduced muscle-venous O(2) storage, exacerbated by ventilatory limitation and dyspnea.
authors.affiliation: Department of Clinical Medicine, University of Rome La Sapienza, viale dell'Università, 37-00185 Rome, Italy. valli.gabriele@fastwebnet.it
authors.forename: G
authors.initials: G
authors.lastname: Valli
authors.forename: A
authors.initials: A
authors.lastname: Cogo
authors.forename: C
authors.initials: C
authors.lastname: Passino
authors.forename: D
authors.initials: D
authors.lastname: Bonardi
authors.forename: G
authors.initials: G
authors.lastname: Morici
authors.forename: V
authors.initials: V
authors.lastname: Fasano
authors.forename: M
authors.initials: M
authors.lastname: Agnesi
authors.forename: L
authors.initials: L
authors.lastname: Bernardi
authors.forename: A M
authors.initials: AM
authors.lastname: Ferrazza
authors.forename: S A
authors.initials: SA
authors.lastname: Ward
authors.forename: P
authors.initials: P
authors.lastname: Palange
mesh_terms: D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000209:etiology / Q000503:physiopathology; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*