Evaluation of blood lactate elevation as an intensity criterion for exercise training.

We sought to determine whether exercise intensities not elevating blood lactate produce alterations in physiological responses to exercise associated with training. Twenty-seven sedentary young men performed five cycle ergometer training sessions.wk-1 for 5 wk. Training power outputs were randomized to power outputs corresponding to either 80% of the lactic acidosis threshold (LAT), 25% delta or 50% delta (where delta is the difference between LAT and peak VO2 power outputs estimated from incremental exercise tests). Exercise sessions were 30 min for the 50% delta group and were proportionately longer for other groups, so that total work did not vary among groups. Before and after training, subjects exercised for 15 min (or to tolerance) at pretraining 80% LAT, 25% delta, 50% delta, and 75% delta power outputs. Continuous O2 uptake, CO2 output, ventilation and heart rate, and end-exercise blood lactate, norepinephrine, and epinephrine were measured. For the 80% LAT group, posttraining end-exercise values for the 75% delta test were significantly lower for each of these variables. There were similar reductions in each variable in all three training groups; no significant differences among groups were seen. Thus, in healthy subjects exercise which does not elevate blood lactate alters constant power output responses as effectively as exercise which elevates lactate, provided that total training work is the same.