“Can’t I get in shape for soccer just by playing more soccer?” my son asked me recently. It’s a natural assumption. After all, your body does adapt to whatever activity you do.

But the answer is “no.”

Think about it. Professionals — the people who play soccer the most — still get hurt doing it. And these injuries can happen when you are several feet from anyone else.

As I mentioned in my previous post, good running form will help you avoid these “non-contact” injuries. But you also need to work on your strength.

By playing a sport a lot, you may strengthen the muscles you use most often in that sport. But just about every muscle has a counterpart that performs the opposite action. You might not use it as much when you are playing, so it doesn’t get as strong. It’s like a car needing both an accelerator and a brake.

For example, soccer players often develop strong quadriceps. Strengthening these muscles in the front of the thigh can also help protect the knee, for example by absorbing force when you land from a jump.

But a soccer player’s hamstrings, the muscles in the back of the thigh, must be strong enough to balance the quadriceps.  Without that balance, the quadriceps may exert too much force on the knee joint, potentially damaging it. Some ACL (anterior cruciate ligament) injuries happen this way.

The same applies to the outer hip muscles, gluteus muscles and core. Soccer players (and athletes in many other sports) should focus on building these muscles. “They’re not so much weak as imbalanced,” says Holly Silvers, a physical therapist who helped design the FIFA11+ soccer injury prevention program.

In addition, many of use spend far more time sitting at a desk than we do playing a sport. While we are sitting, our muscles adapt to that position, which is the opposite of what we need them to do on the playing field.

Restoring balance to these muscle groups protects not only knees but also ankles, groins, feet, calves, shins, Achilles tendons and everything else below the waist.

To show you how to strengthen these muscles, I’ve collected some videos based on the FIFA program as well as Sportsmetrics from the Cincinnati Sports Clinic. You should perform these exercises after warming up with the running exercises in the previous post:

1. Hamstrings

This exercise, called the Nordic (or Russian) hamstring exercise not only strengthens the hamstrings, it strengthens their ability to do the eccentric contractions they make to balance the concentric contractions the quadriceps make.

(video by Marc Sand)

2. Core

An advantage of these core-building exercises is that they strengthen the muscles in the trunk without stressing the lower back.

(video by Expert Village)

(video by Expert Village)

3. Hips

Hips move in multiple directions, and these exercises capture most of them.

(video by Chad Madden)

(video by eHow Fitness)

These exercises will help with other sports besides soccer. And they’re likely to increase your performance as well as protect you from harm.

Try to do them two or three times a week. You may find you’re most likely to remember if you do them just before or after you play. (They can substitute for those stretches you used to do.)

If you get bored of these, let me know. I can help you find variations to strengthen the same muscle groups.

But you’ll need more than these to protect yourself from injury. In my next article, I will lay out some exercises that improve your agility and power.