Effects Of Prolonged, Fatiguing Exercise On Critical Power

Abstract

The critical power (CP) is an important parameter of aerobic fitness and a strong predictor of endurance performance. Establishing how prolonged, fatiguing exercise may influence the CP is important for accurate performance prediction. PURPOSE: To assess the reliability of the CP in a fatigued state established using a 3-min all-out cycling test (3MT), and to assess the effects of fatigue on CP. METHODS: Subjects in Study 1 (n=6, 31 ± 6 yr, 76.8 ± 6.7 kg) and Study 2 (n=9, 29 ± 11 yr, 75.9 ± 7.1 kg) completed a ramp incremental test, a control 3MT test (C-3MT) and a 3MT immediately following 2 h of heavy-intensity constant work-rate (CWR) cycling (F-3MT). In Study 1 subjects performed the F-3MT condition twice. In Study 2 subjects completed 2 h of heavy exercise immediately followed by CWR exercise to exhaustion at 15 W above and below CP measured in F-3MT. Oxygen uptake (VO2) and blood [lactate] were measured during all tests. RESULTS: In Study 1, CP estimates from repeated F-3MTs were not different (test 1: 273 ± 52 W vs test 2: 276 ± 58 W; P >0.05), with an intraclass correlation coefficient of r=0.99 (P<0.05) and typical error of 5 W (2%). In Study 2, CP was lower in the F-3MT (282 ± 52 W) compared to C-3MT (306 ± 56 W; P<0.05). Four of nine subjects completed 30 min of exercise below F-3MT CP with sub-maximal steady state VO2 and blood [lactate] profiles, whereas five subjects exhibited steady state VO2 but non-steady state blood [lactate] and reached exhaustion in ~9-18 min. Subjects reached exhaustion in ~4-22 min when exercising above F-3MT CP. The VO2peak and end-exercise blood [lactate] were not different between exercise bouts performed above (4.05 ± 0.41 L·min-1) and below F-3MT CP (3.93 ± 0.50 L·min-1) but the VO2peak values were lower than the VO2max in the ramp incremental test (4.33 ± 0.52 L·min-1) (both P<0.05). CONCLUSION: The CP estimated in a 3-min all-out test evidenced high reliability in a fatigued state. We found that exercise in close proximity below the CP in the fatigued state was not sustainable beyond ~18 min and did not exhibit steady state blood [lactate] profiles. The VO2 responses during exercise above and below CP were characterised by inability to attain the same VO2max as in the rested state. These findings suggest that the well-characterised physiological definition of the CP is altered under conditions of extreme fatigue.