Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC200
An exercise test to characterise the domains of aerobic function in humans
S. R. Murgatroyd1, L. A. Wylde1, D. T. Cannon1, H. B. Rossiter1
1. Institute of Membrane and Systems Biology, University of Leeds, Leeds, United Kingdom.
The consistent physiological signal for impending exercise intolerance is the failure of oxygen uptake (VO2) to meet the energy demands of the task in a steady state . The upper limit for steady state exercise is demarked by critical power (CP), which is the asymptote of the hyperbolic relationship between power output and tolerable duration . Together with the lactate threshold (LT) and VO2max, CP partitions the domains of aerobic function that cluster power output ranges by their common physiological response characteristics . There is currently no exercise testing protocol, however, to determine LT, CP and VO2max in a single laboratory visit. Given that CP is the highest sustainable power output following intolerance at VO2max , we reasoned that a maximum sustained effort immediately following standard ramp-incremental exercise  would allow the domains of aerobic function to be estimated in a single test. Eight healthy men (21-30 yr) performed a series of cycle ergometry (Excalibur Sport, Lode, NL) protocols. Following familiarisation participants performed ramp exercise to intolerance with the incrementation rate computer-controlled at 20 W/min, immediately followed by a 3-min all-out ‘sprint’ (ramp-sprint test; RS) for the measurement of cadence-dependent power output (CPRS). On separate days participants performed a series of 4-5 constant-power tests (gold-standard method; GS ) to estimate CPGS and VO2max-GS. Subjects also completed constant-power tests (for 30-min or to intolerance) at work rates corresponding to 10 W below LT and CPRS, and 10 W above CPRS to verify the steady state estimate. Breath-by-breath VO2 and capillary blood [lactate] were measured using a mass-spectrometer and turbine (MSX, NSpire, UK) and enzymatic oxygen-rate method (GM7, Analox, UK). From these measurements CP and VO2max were compared (t-test) between RS and GS tests. LT averaged 2.0±0.3 L/min (mean±SD). CPRS (255±52 W) and VO2max-RS (4.0±0.7 L/min) did not differ (p = 0.8 and 0.7) from CPGS (256±48 W) and VO2max-GS (4.0±0.6 L/min). Exercise 10 W below LT and CPRS was sustained for 30±0 min with VO2 and blood [lactate] in a steady state. Exercise 10 W above CPRS caused the attainment of VO2max (4.0±0.6 L/min) and peak [lactate] (11±2 mM) in 20±5 min. Consistent with the hypothesis the RS test accurately identified all three indices of aerobic function with a precision of 8, 3 and 4 % (for LT, CP and VO2max), which compares favourably to current methods [1,2,4]. The single-visit RS test also provided an estimation of the upper steady state limit to within 4 %. These data suggest that the domains of aerobic function may be reliably estimated from a single maximal exercise test with non-invasive measurements. The RS test may, therefore, simplify the characterisation of aerobic function and monitoring of exercise training, therapeutic and/or experimental interventions.
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