I have received this question many times so think I might share with you my thoughts on aerobic training and interval training.
The Purposes and Benefits
Endurance/ Aerobic training is to exercise with your heart rate under 75% max, it is often used for base building and ultrarunning/ exercise 3+ hours.
By keeping a fairly low heart rate (and a constant pace), you teach your body to use fat as fuel and spare muscle glucogen in order to delay muscle fatigue. We often use base building to improve endurance.
Interval training can be done in forms of strength and/ or aerobic, i.e. farklek running/ cycling, etc.
By keeping heart rate from 90% max to 100% (sometimes over 100% for a short burst) and stressing the lactate threshold, our heart muscle is strengthened thus improving oxygen transportation.
Muscle glycogen is used in this training, hence, interval last no longer than 5 minutes. We usually do interval training to improve speed and muscle strength.
In conclusion, aerobic training and interval training stimuate different muscle groups. My suggestion is if you are a beginner, do aerobic training for 2 weeks and add 1 interval session/ week to reap full benefits.
Be Your Best,