In running as with other endurance sports lactic acid threshold (the point at which lactic acid reaches a critical level in an athlete's blood) is widely regarded as one of the chief determining factors in athletic performance. As such it is important for athletes to train in a way that increases the rate at which lactic acid is absorbed and processed by the body (the liver in particular). In order to accomplish this sort of training several important variables about an athlete's physiology must be known the most important of which, and the one we will primarily be discussing, is the specific heart rate zone that corresponds to the lactic threshold. For most people the lactic threshold is reached when the blood lactate concentration reaches 4-4.5 millimoles (mM). However since most athletes do not have ready access to the equipment necessary to accurately read lactate levels through blood sampling other types of tests can be use, or if accuracy is not something you consider important in your training a simple formula can be used.
LT is generally said to fall between 80%-85% of your max heart rate,
so you can theoretically find max heart rate and then extrapolate from
there, and the formula would look something like this.
(220-age) x 0.80 = Min. LT and (220-age) x 0.85 = Max. LT
So by this estimation if you are a 22 year old male your lactic
threshold (LT) would fall somewhere between 160-170 BPM which is a
pretty wide scale and could be off by as much as 10% which when you
figure a max heart rate of 200 BPM could be as much as 20 BPM which is
huge when you are trying to pin point a specific heart rate zone for
training. For example max heart rate is meant to be 220 minus age, so my
max should be 197, in reality it is 215 so the calculations would be
way off in my case.