title: Pulmonary O2 uptake kinetics as a determinant of high-intensity exercise tolerance in humans.
abstract: Tolerance to high-intensity constant-power (P) exercise is well described by a hyperbola with two parameters: a curvature constant (W') and power asymptote termed "critical power" (CP). Since the ability to sustain exercise is closely related to the ability to meet the ATP demand in a steady state, we reasoned that pulmonary O(2) uptake (Vo(2)) kinetics would relate to the P-tolerable duration (t(lim)) parameters. We hypothesized that 1) the fundamental time constant (τVo(2)) would relate inversely to CP; and 2) the slow-component magnitude (ΔVo(2sc)) would relate directly to W'. Fourteen healthy men performed cycle ergometry protocols to the limit of tolerance: 1) an incremental ramp test; 2) a series of constant-P tests to determine Vo(2max), CP, and W'; and 3) repeated constant-P tests (WR(6)) normalized to a 6 min t(lim) for τVo(2) and ΔVo(2sc) estimation. The WR(6) t(lim) averaged 365 ± 16 s, and Vo(2max) (4.18 ± 0.49 l/min) was achieved in every case. CP (range: 171-294 W) was inversely correlated with τVo(2) (18-38 s; R(2) = 0.90), and W' (12.8-29.9 kJ) was directly correlated with ΔVo(2sc) (0.42-0.96 l/min; R(2) = 0.76). These findings support the notions that 1) rapid Vo(2) adaptation at exercise onset allows a steady state to be achieved at higher work rates compared with when Vo(2) kinetics are slower; and 2) exercise exceeding this limit initiates a "fatigue cascade" linking W' to a progressive increase in the O(2) cost of power production (Vo(2sc)), which, if continued, results in attainment of Vo(2max) and exercise intolerance. Collectively, these data implicate Vo(2) kinetics as a key determinant of high-intensity exercise tolerance in humans.
authors.affiliation: Institute of Membrane and Systems Biology, Faculty of Biological Sciences Worsley Bldg., Clarendon Way, Univ. of Leeds, Leeds, LS2 9JT, UK.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Murgatroyd
authors.forename: Carrie
authors.initials: C
authors.lastname: Ferguson
authors.forename: Susan A
authors.initials: SA
authors.lastname: Ward
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Whipp
authors.forename: Harry B
authors.initials: HB
authors.lastname: Rossiter
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000704:Analysis of Variance; D001642:Bicycling; D004739:England; D015444:Exercise; D005080:Exercise Test; D017079:Exercise Tolerance; D006801:Humans; D007700:Kinetics; D019344:Lactic Acid / Q000097:blood; D016014:Linear Models; D008168:Lung / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange; D055815:Young Adult
chemical_list: D019344:Lactic Acid; D010100:Oxygen