Abstract des Autors

Several studies have shown the inadequacy of determining lactate threshold (LT) by using a ramp protocol during cycle ergometry exercise, since a lack of coincidence was evidenced between lactate and ventilatory thresholds. The purpose of this paper was to investigate the relationship existing between ventilatory threshold (VT) determined in a laboratory setting using a treadmill ramp protocol, and LT determined in a field test. Twenty-four trained children performed both types of tests. For the laboratory testing, treadmill speed was increased by 0.1 km/h every 5 seconds, and the protocol was continued until volitional fatigue. Ventilatory data were plotted against heart rate and treadmill speed. The field test consisted of an incremental protocol of 3-minute-stages, and subject running velocity was increased by 1 km/h per stage. The protocol was continued until volitional fatigue. Lactate data were plotted against heart rate and running velocity. The results showed significant differences in mean values of heart rate and running pace at VT and at LT, between the laboratory and the field tests, respectively. The ventilatory parameters obtained at maximum intensities in the laboratory tests were similar to those reported in previous studies. The lack of coincidence between LT and VT may be explained by an increased efflux of hydrogen ions - independent from the lactate carrier - from muscle fibers to the blood stream during the laboratory ramp protocol. Verf.-Referat