Alteration in the Lactate Threshold with Changes in Substrate Availability*

Abstract

The lactate threshold (LT) was studied (N=9) during ergometer cycling under control (C), high blood glucose (G), and high blood free fatty acid (F) conditions. During the G trial blood lactate (HLa) was greater than C at all work loads (P less than 0.05) Adjusted blood HLa values (HLa - pre-exercise value = delta HLa), however, were essentially the same for the C and G trials. Determination of the LT disclosed that there was no difference between the two treatments (C = 53.9 +/- 2.6% VO2 max; G=52.7 +/- 3.1% VO2max). Elevation of blood FFA levels, however, reduced both the HLa and deltaHLa at all work loads from 150-250 W (P less than 0.05) although VO2 was the same as C. In addition, a significant increase in the LT (F = 59.8 +/- 2.6% VO2max) was found for the F treatment. These data suggest that (1) the LT can be altered by substrate availability and (2) that muscle tissue anoxia may not be solely responsible for lactate production during submaximal work.