Developing both speed and endurance is the recipe for running faster.
Speed is a combination of strength and power.
Force is the maximum force your muscles can produce. It develops through hill training, but also with some weight training that should target the lower body.
Power is a neuromuscular capacity that depends mainly on the strength to which muscle fibers can be recruited for the execution of force and then movement. You train through short sprints and tracks that repeat workouts. For example, repeats of short 60m sprints with full recovery is a great way to stimulate the neuromuscular system in a way that you are forced to apply as much force as possible in a very short period of time.
Less structured types of exercise such as fartlek or lunges are also used to develop speed; These are methods that do not lead to a high level of fatigue and at the same time significantly improve the speed-oriented capabilities of the runner. The neuromuscular system is proven to have memory, so not stimulating speed-oriented components during training is a sure way to not be successful at being fast in the future.
When strength and power improve, and speed is brought to an acceptable level, the next step is to work to maintain this speed for a longer period. After all, it is the overriding principle of long-distance running: run fast and long. Resistance to speed is the term used to describe this ability; it is based on the ability of the muscles to maintain high and rapid force production for longer.
The challenges to be faced when endurance training is the production of lactic acid in the tissues at a certain rate called the Lactate Threshold. The fine art of training is to raise the threshold to maintain a good speed for a long period of time. It is true that the lactate threshold rhythm can be maintained for an hour. So it’s just above the half-marathon pace for non-elite runners.
To train endurance for speed, you need to do medium to long reps on the track at a pace above the lactate threshold. That means, for example, 800 meters or 1k of reps at a 5k running pace. Recovery should be brief so that the muscles do not have a chance to fully recover, and then simulate the endurance conditions and rigor of running.
Finally, work below the lactate threshold to do longer reps or divided tempos for a duration that could extend to an hour at a marathon pace. This type of work allows you to precisely position yourself in the race conditions and teach the muscles exactly what speed to maintain during this given time (sometimes feeling so long during the race).