Interval training involves exercising at an intensity close to or exceeding individual's maximal aerobic capacity (VO2max). It has been widely used in endurance training to improve aerobic performance. One of the benefits of doing interval training is the improvement to anaerobic threshold (AT), also known as maximal lactate threshold.This is the point at which maximal lactate production is equal to maximal lactate clearance. At AT, there is also an increase in anaerobic metabolism.
Exercising below AT is commonly known as exercising at steady state. Individuals will be able to sustain this intensity for a long period of time. However, when one exercises at an intensity above AT, he/she will not be able to sustain the intensity for long. Therefore, increasing AT level is essential for improving aerobic performance.
It is a common misconception that lactic acid is the cause of fatigue during high intensity. When lactic acid is produced, it actually dissociates to lactate and hydrogen ion very rapidly.
The lactate is transported by the blood to the liver to be converted to glucose. The H+ is the molecule that is responsible for causing interference with muscle contraction and the burning sensation individuals feel when exercising at high intensity.
When individuals increase their AT, their ability to buffer the H+ improves. This is one of the reasons why having a high AT will benefit aerobic performance.
The training distance and intensity for interval training is dependent on individuals' fitness goal. For individuals who are trying to improve their performance for long distance events, it is recommended for them to do long intervals that last between 3 to 5 minutes. Long interval training requires one to exercise at around 90-100% of VO2max. At this intensity, individuals will be able to train at an intensity above their AT, which is normally 60-75% of VO2max, while not having to alter their usual running mechanics to a large extent.
The common running distance for long interval training is 1km. And the work to rest ratio is between 1:½ to 1:1. Individuals should aim to complete 3-8 intervals of 1km in about 3-4½ minutes, and rest 1½-4½ minutes between each interval. Individuals should utilise low intensity active recovery like walking or slow jogging, instead of complete rest, during the recovery period between intervals.
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