Of course everyone is different, but my experience - reading articles written by elite level coaches and being coached by elite level coaches - is that there are very commonly held principles that are recommended by exercise physiologists and well trained, expert coaches.

Like others have said:

Almost all (approximately 80+ percent) of your training should be at level 1 or 2 which is also known as the aerobic zone. 60-80% of your max heart rate. The "easy talking" zone. Also known as base training.


The other 20% of your training should be INTELLIGENTLY PLANNED intensity training.

The zones between "easy/aerobic" and "intense" should be avoided because they don't serve any purpose in improvement - it neither is optimal for base training, nor does it provide the benefits of intensity training.

Examples of intensity training are pickups, race pace work outs, time trial work outs, races, intervals etc. The type, duration and frequency of intensity training should be part of a plan oriented toward a goal - and that goal depends on the distance, speed, etc. you want to achieve. A 5 K high school XC runner will have a different plan than a marathoner, although the principles will be the same.

Intelligent, planned intensity is not done at 100%. It is almost always done at an intensity, duration, etc. that is intended to incrementally improve some aspect of your performance.

For instance, "intervals" are generally not done at maximum output. They are generally intended to be just above the rate/speed you want to perform at in competition to gradually push that higher. So if you run a 4 minute mile, your intervals might be about 10% faster than that rate, for shorter distances, repeated.

Just like if you want to train yourself to be stronger, you don't go out and lift your maximum weight once per day, but you gradually increase your strength with sets or repetitions.

They are generally done at an intensity that can be sustained through several repetitions with the final one being either faster/stronger or at least equal to the first. This sort of thing cannot be done if the early reps are done at too high a level.

The other, less intense training (the aerobic training) should be done in a way so that base can be built, but also so that the body isn't so tired that you can't put out the effort you need on the intensity days. Also, over all training has to be intelligently designed to avoid injury and creeping fatigue (over training).

A lot of times young people don't understand this because they have incredible untapped reserves and see huge improvement regardless of whether their techniques are optimal or not. What they don't know is how much better, and/or easier they could train for better results. Many coaches, especially if their only qualification is that they are themselves good athletes and are youngish don't know either.

Pushing yourself to the point of pain as a regular training technique is not what elite coaches do and I've NEVER seen an expert who recommends it.