Effects of stage duration in incremental running tests on physiological variables.

To study the effect of stage duration on some physiological variables in an incremental running test, 8 well-trained runners underwent 3 running tests, with stage durations of 1, 3 and 6 min. To study maximal lactate steady state (maxLASS) and its corresponding speed, every subject underwent a 4th test with three 15-min stages at three speeds, based on the running speed at 4 mmol/l blood lactate (V4) in the 6 min per stage protocol. The first load in the 15 min per stage test was V4 - 0.5 km/h, the second at V4, and the third V4 + 0.5 km/h. To compare the maxLASS speed with outdoor performance, the subjects also ran 5 km at this speed on an outdoor track. Mean maximal running speed (V (max)) in the incremental test was significantly lower in the 6-min (15.1 km/h) and 3-min stage protocol (17.1 km/h), compared with the 1-min stage protocol (18.3 km/h). Mean peak VO (2) and mean peak heart rate were not different between the protocols with different stage duration. The mean V4 was significantly lower in the 6 min per stage protocol compared with the 3 min per stage protocol (12.9 vs. 14.4 km/h). Mean ventilatory threshold was not different between the 1, 3 and 6 min per stage protocols. No threshold behaviour was found in respiratory rate. MaxLASS can be estimated from V4 in the 6 min per stage protocol, and verified by three 15-min intensities being V4 - 0.5 km/h, at V4, and V4 + 0.5 km/h. The mean blood lactate concentration at the maxLASS speed was not different between treadmill running and outdoor running on a track. In conclusion, for measuring peak values of physiological variables in an incremental running test, the duration per stage is of less importance, however, when measuring blood lactate concentration as a function of running speed, the duration per stage should be at least 6 min.