How important is the lactate threshold to running and cycling performance?

Your lactate threshold essentially defines the upper limit of your sustainable pace in training and competition. Once you cross over your lactate threshold and blood lactate accumulates, this hinders the functioning of the working muscles, it becomes very difficult to sustain that particular pace and fatigue sets in. Two athletes with the same level of fitness (VO2max) can have very different running paces because their lactate threshold occurs at difference percentages of their VO2max. In the example presented in figure 2, athlete 1 and athlete 2 have the same level of fitness (VO2max) but athlete 1’s lactate threshold occurs at 60% of their VO2max corresponding to a running speed of 6.8 miles per hour, where as athlete 2’s lactate threshold occurs at 70% of their VO2max, which corresponds to a running speed of 7.8 miles per hour. Thus even though both athletes have the same level of fitness (VO2max), athlete 2 has a higher lactate threshold, can work at a higher percentage of their VO2max and thus can maintain a greater running speed. In this example Athlete 2 will cover the race distance quicker than athlete 1.