Critical Power Measurement

Critical Power (CP) represents the highest sustainable power output (PO) at which physiological steady-state can be achieved.. In cycling exercise, CP is traditionally derived from the PO versus time-to-exhaustion (TTE) relationship based on 3-5 TTE trials ranging from 1 to 20 min. Recently, a 3-min all-out test (3M) has been proposed for CP estimation. However, CP derived from this test has not been externally validated (i.e., corroborating steady-state lactate concentration [La] for prolonged durations of cycling at the value associated to CP). PURPOSE:To compare CP derived from 5 TTE and the 3M test, and to validate these values against a maximal lactate steady-state (MLSS) test. METHODS:Seven healthy young subjects (28±3 yrs; 68.4±7.3 kg; 175±9 cm) were tested. A ramp incremental test to exhaustion was performed on a cycle ergometer (Velotron Dynafit Pro, Racer Mate, Seattle, WA, USA) to determine VO2peak, gas exchange threshold (GET) (Quark CPET, Cosmed, Rome, Italy), and peak power output (POpeak). CP from the 5 TTE test was calculated with a 2-parameter hyperbolic model (HYP). The 3M test was performed using the linear mode of the cycle ergometer, and CP was calculated as the mean PO of the last 30 s of the test. MLSS was considered as the highest PO during a 30-min constant load ride with a variation in [La] ≤ 1.0 mM·L-1 between the last 20 min of exercise ([La] measured every 5 min). RESULTS:Mean VO2peak, GET, and POpeak were 4.30±0.67 L·min-1, 2.60±0.30 L·min-1, and 383±53 W, respectively. PO at CP HYP (267±39 W), CP 3M (258±52 W), and MLSS (246±37) were not different (p>0.05). Bland-Altman plots comparing CP from HYP and 3M against the PO at MLSS showed no significant biases but wide limits of agreement (LOA) ranging from -8 to 51 W (bias=21 W) and from -43 to 68 W (bias=13 W), for HYP and 3M, respectively. When comparing CP from 3M to HYP, the LOA ranged from -43 to 26W (bias=-9 W). CONCLUSIONS:Although the POs associated to CP as estimated from the 5 TTE, the 3-min all-out test, and MLSS were not different, the large variability in the CP amongst methods results in poor accuracy of CP estimation and detracts from the practical application of this test.

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