The effects of training intensity on blood lactate breakpoints in runners

The purpose of this study was to determine the effects of an eight week running endurance training program at two different intensities on both aerobic (AeT) and lactate turn point (LTP) thresholds. Twenty-nine male middle distance runners volunteered to participate in this study. Subjects were randomly assigned to 3 groups: two experimental and one control. The low intensity (LI) group trained at HR corresponding to the AeT. The high intensity (HI) group trained at HR corresponding to the LTP. The training contents of the control (C) group was not supervised: they combined mixed athletic training program with sports games. All subjects underwent an interval incremental running test before and after the training program in order to determine the changes if any in AeT, LTP and heart rates (HR) corresponding to these thresholds. Two breakpoints were determined in the lactate (LA) running velocity curve. The LTP was determined as the second abrupt increase of La around 4 mmol·l-1 by means of computer-aided linear regression breakpoint analysis. The AeT was defined as the first increase of LA above resting level. The analysis of training induced changes revealed a significant increase in both AeT and LTP for HI group (p<0.05). The increase of LTP was a little greater than that of AeT (6,8% versus 5,5%). However, these thresholds did not change significantly in C or LI groups. No significant difference either in HR or LA variables in either of the groups was observed. These results seem to indicate that only training program at the intensity of LTP produces an increase in both aerobic-anaerobic transition characterizing variables (AeT and LTP) while the training at the AeT intensity does not cause any changes of these thresholds in moderately trained runners.