Effects of Two Hours of Heavy-Intensity Exercise on the Power-Duration Relationship

Introduction Changes in the parameters of the power-time relationship (critical power (CP) and W) during endurance exercise would have important implications for performance. We tested the hypotheses that CP and W, estimated using the end-test power (EP) and the work done above EP (WEP), respectively, during a the 3-min all-out test (3MT), can be reliably determined, and would be lower, after completing 2 h of heavy-intensity exercise. Methods In study 1, six cyclists completed a 3MT immediately after 2 h of heavy-intensity exercise on two occasions to establish the reliability of EP and WEP. In study 2, nine cyclists completed a control 3MT, and a fatigued 3MT and constant power output tests to 30 min or the limit of tolerance (T-lim) below and above F-EP after 2 h of heavy-intensity exercise. Results In study 1, EP (273 52 vs 276 +/- 58 W) and WEP (12.4 +/- 4.3 vs 12.8 +/- 4.3 kJ) after 2 h of heavy-intensity exercise were not different (P > 0.05) and were highly correlated (r = 0.99; P < 0.001). In study 2, both EP (F-EP: 282 +/- 52 vs C-EP: 306 +/- 56 W; P < 0.01) and WEP (F-WEP: 14.7 +/- 4.9 vs C-WEP: 18.3 +/- 4.1 kJ; P < 0.05) were lower after 2-h heavy-intensity exercise. However, maximum O-2 uptake was not achieved during exercise >F-EP and T-lim was shorter than 30 min during exercise <F-EP (18.2 +/- 10.7 min). Conclusions The EP and WEP may be reliably determined after 2-h heavy-intensity exercise. The 8% and 20% reductions in EP and WEP, respectively, have important implications for performance during endurance exercise. The physiological characterization of EP (and, by extension, CP) may differ in a fatigued compared with a rested state.