Nikoluski, the research that I have found to be most meaningful regarding exercise physiology (of which Viru’s work is definitely among the work that is at the top of my list) suggests that the anaerobic threshold is very closely linked with to the point in which an “equilibrium exists between lactate formation and elimination”. This point, according to Viru, tends to lie between the range of 75-90% of VO2 max in trained athletes.
the degree to which this information is useful in regards to training an athlete, such as a quarter miler, is such that work may be carried out via the use of a HR monitor that ensures that the work is performed at the highest intensity of max HR possible (beneath the anaerobic threshold) in order to yield the adaptations necessary to elevate the anaerobic threshold.
The elevation of the anaerobic threshold would then:
The overall point being to delay the onset of the glycolytic process as much as possible.
So as only one example, providing that the requisite speed work is also being conducted appropriate for 400m needs, either of these cases (in reference to an actual competition) would provide for more energetic resource to be used at the end of the race for a stronger finish.
Point two is a bit tricky because higher intensity in the 400m is a speed issue and so training to improve the anaerobic threshold beyond a certain point can run counter to this goal. That is why the emphasis must always be on the quality of the Special Endurance elements. You will always know the positive and negative influences while there’s still time to do something about it.