The race is a sport that is identified with weight loss because it is eminently aerobic, but depending on how we do our workouts we can focus the race to lose fat or even help us maintain or gain muscle mass. Everything also depends on our previous form.
First of all, if you are not used to running, the first few days you will experience a certain amount of muscle gain, since running is an activity that requires the strength and endurance of the lower body. But there comes a time when this hypertrophy stops and is no longer so noticeable, so if we want to gain more muscle by running we will have to adapt the training.
The short and intense series are the ones that are going to make the muscles of the legs grow a little more. As with weight work, the muscle needs an intense stimulus to grow in thickness, so series of 100 to 400 meters to 90% or more of intensity can serve to hypertrophy.
The problem with this is that it requires a good running technique and a good aerobic base to support these workouts. We can’t go from zero and run like crazy until we can’t run anymore because we’ll end up injured. Once we’ve been at it for a month or so and can ride comfortably is when we will introduce the work of these series.
The breaks between series must be almost complete to be able to do the next one at a high intensity. At most 6-8 series per session and let these muscles rest for at least 24 hours, just as if we had gone to the gym, so that rest along with proper nutrition (essential if we want our muscles to grow) makes the leg muscles grow correctly.
You also have to be aware of the limitation that the race has to grow these muscles. Depending on our running technique and its own bio mechanics, there will be muscles that will not be worked as much and whose hypertrophy will be limited, so the ideal is to complement it with weight work in the gym.
Finally, to say that if we want our muscles to grow in a remarkable way, simply with the race it is going to be difficult to achieve it, if we just want to tone up and gain some muscle mass this type of training if it can be good for us.