Does cardio replace leg training?

Those who do another sport besides strength training, such as soccer, often ask themselves if they can do cardio instead of leg training. After all, cardio also puts a strain on the legs. In today's article we will clarify for you whether or not cardio can really replace leg training.

Differences in the muscle fibers

Your muscles are made up of muscle fibers, which are divided into different types with different properties. Depending on the type of fiber, the color, number of mitochondria (energy production), volume, and contraction speed differ, among other things.

Basically, there are two types of muscle fibers. However, the fiber type has 2 other subordinate categories.

Type 1 muscle fibers

The red type 1 muscle fibers are the so-called endurance muscle fibers. They are also called slow-twitch muscle fibers.

By twitching, we mean the speed of contraction, which is slow in type 1 muscle fibers. But they are persistent and do not tire quickly.

The reason for this is a higher number of mitochondria compared to the other fiber types. Thus, more energy can be provided. Furthermore, the red muscle fibers are rather thin and do not thicken as quickly.

It has been scientifically proven that endurance athletes have a higher proportion of type 1 muscle fibers than the average. This is significantly higher than their proportion of type 2 muscle fibers.

Type 2 muscle fibers

Type 2 muscle fibers are divided into muscle fiber types 2a, 2x, and 2b. These fibers are white and have an increasing contraction speed from type 2a to 2b.

For this reason, they are also called fast-twitch muscle fibers. They are the exact opposite of type 1 muscle fibers. They are less persistent, are very bulky, and have a lower number of mitochondria.

The fast-twitch muscle fibers (type 2b) are activated primarily during weight training. The more muscle fibers of this type a strength athlete has, the better. But sprinters also have a higher proportion of type 2b muscle fibers.

Still, you can effectively build muscle even with a relatively small percentage of these fibers by making your existing type 2b fibers as powerful as possible.

Furthermore, the muscle fiber distribution of your body is not even. For this reason, many strength athletes often have problems getting their calf muscles to grow. These often have more type 1 muscle fibers and are therefore more suited for endurance.

Differences in the stimuli

Resistance

Cardio and strength training differ in the stimuli to which your body is exposed. One of the factors that is enormously important in weight training is resistance.

If you want to build muscle effectively, you need to stimulate your body with increasingly higher resistance again and again. With cardio, however, you can hardly increase the resistance. This is important for strong leg muscles.

With classic leg training, on the other hand, you can increase the resistance as much as you want. You could wear a weight vest while running or increase the resistance while cycling, but it would be very difficult to achieve progression over a longer period of time.

With cardio, the resistance is too low and (hardly) able to be increased.

Different angles and variations

If you want strong, pronounced leg muscles, you should train them from different angles with different variations. With the right equipment in the gym, this is no problem.

However, it's hardly possible to load your legs from different angles during cardio. With running, you could theoretically choose an elevated route instead of a flat one, for example, but cardio doesn't really offer much more choice than this.

As a result, you have a consistent pattern of movement. In the gym, on the other hand, you can load your legs with different variations.

Cardio won't let you work your muscles from (enough) angles.

Supplementary training

So in terms of the stimuli, cardio can't keep up with leg training. Furthermore, cardio tends to activate type 1 muscle fibers. However, the activation of type 2b muscle fibers is more important in strength training.

However, cardio is still a good idea. While you can't completely replace leg training, cardio is a good complement to weight training. With cardio, for example, you promote blood circulation in your body, strengthen your cardiovascular system, and can even improve your recovery.

If your goal is to develop your strength and muscle mass, you should not do a strenuous cardio session before strength training.

Otherwise, you won't have enough energy for a really challenging strength training session. If the training session did not stress your legs, you can also do a short cardio session after your strength training. However, it is generally best for your recovery if you separate cardio and strength training and do them on separate days.

You should not do strenuous cardio sessions before strength training. However, a relaxed warm-up program of about 5-10 minutes on a cardio machine IS recommended before strength training.

Conclusion

Your leg muscles are loaded during cardio, but it's mainly the type 1 muscle fibers that are used. During leg training, however, the fast-twitch type 2b muscle fibers are stressed.

Furthermore, with cardio you don't have the same training options that you have with strength training. You don't have a wider selection of exercises, you don't have much variation in your workout, and it's hard to increase resistance. However, all of these factors make for a good leg workout when you do strength training.

You cannot replace leg training with cardio. However, you should not necessarily do only strength training and forego cardio either.

Cardio offers many health benefits. It improves your cardiovascular system, which is heavily stressed during strength training. In addition, it promotes blood circulation and can improve your recovery.

Avoid strenuous cardio sessions before strength training. If you haven't trained your legs, you can do cardio after the workout. However, it is recommended to schedule cardio and strength training separately and do them on separate days.