If you want to progress qualitatively, minimize the likelihood of injury, strengthen the heart, train muscles, then it is important to know that everything should be uniform in running. Either it is uniform motion or it is uniform acceleration.
Consistency in running pace
When you are doing a run, it is very important to know what exactly you are doing it for. For example, if you need to develop stroke volume, then you run at a slow pace with a heart rate of about 70-80% of your maximum. When running like this, you need to maintain an even average pace that will keep your heart within the stated heart rate range.
If you run in spurts, then the training will already lose the main task that was assigned to it. And the slow run will turn into a fartlek. That is, a chaotic alternation of slow and fast running. And fartlek's tasks are different from the workout you are doing.
If you are doing interval training, there should be consistency during your tempo segments and during your recovery run. For example, you have a task to train the threshold of anaerobic metabolism. To do this, you need to complete 3 segments of 3 km at a heart rate of 90% of your maximum. That is, again, you will have to maintain a certain average pace for this during the tempo run. Otherwise, you will not be able to maintain the intensity range you need.
And during recovery stretches, the twitching of the pace will only interfere with the rapid recovery.
And so in everything. Even the best form of running tactics, "negative split", which implies that the first half of the distance is covered more slowly than the second, still basically implies running evenly over two halves of the distance. Slightly slower in the first half. In the second half, a little faster.
As with any rule, there are exceptions to this. The exceptions are start and finish accelerations and fartlek. Otherwise, the effect of uniformity always works in preparation.
Uniformity in load growth
Uniform means the same throughout. In this case, during your training. And the load build-up should also be the same.
When preparing for long distances, it is important to run a long run once a week. It must be gradually increased, bringing it to certain values that are required in preparation for a particular distance. And this increase should be the same throughout the training. For example, once a week, increase the length of the race by 1-2 km. It would be wrong if after 4-5 weeks you want to increase the mileage of a long race by 5-7 km. This can easily lead to overwork.
If you do some kind of tempo work, then with an increase in training, the pace of such races will grow by itself. And this growth will also be uniform.
As for the tempo, I would like to add that there will be one more point, which will consist in the fact that as your readiness increases, the increase in tempo will gradually slow down. If at the beginning you can increase your average pace, for example, from 7.00 to 6.30 at a heart rate of 150 for 3 months. The faster you run, the more time you will spend on improving your pace relative to your heart rate. It will kind of slow down progress. But it will also be uniform. In physics, this is called "equally slow motion". That is, we are still faced with the principle of uniformity. Let in this case uniform deceleration.
