Bull riders. Long jumpers. Runners. Tennis, football, baseball, basketball, hockey and soccer players. Professional athletes and weekend warriors.

Dr. William C. Meyers has treated them all. What they shared were injuries that used to be called sports hernias but now are referred to as core injuries.

In 2013, he established the Vincera Institute. Located in Philadelphia, it is dedicated to prevention, diagnosis and treatment of core injuries. His recent book, "Introducing the Core: Demystifying the Body of an Athlete," distills what he has learned over the decades. Here are excerpts from a conversation about that:

Q: We hear the word core a lot. What, exactly, does that mean?

A: It's the trunk. Think of it as the strike zone in baseball. The core includes everything in there. It's a network of muscles, tendons, ligaments and joints. It's major organs and large blood vessels.

It's important because it's our engine room. It's where the center of our body is in terms of athleticism, in terms of movement. It has a tremendous amount to do with controlling the upper extremities and lower extremities.

Q: Why are core muscle injuries so common?

A: Everyone is susceptible to them. Like most of us, as you progress in life, you get occupied by your profession, your children. You get out of shape. Then you try to get back into shape. If you get too vigorous, and you haven't been using those muscles for a while, you rip them apart.

There are 35 different muscle groups in there. Any one of those can be injured. It really comes down to use, overuse and understanding that you've got to apply these muscles together.

If you injure one of the muscles, you start to compensate with the other muscles, and you wind up with a compensatory tug-of-war. The cartilage rubs, and it hurts. The whole art of treating these injuries is figuring out where the primary problem is and where the secondary, compensatory injuries are. It's usually a matter of repairing the primary, and then loosening the secondary ones.

Q: Are any new developments on the horizon?

A: There are some important ones. They all have to do with understanding the far-reaching nature of these injuries. It turns out that there is a connection between core injuries and cognition and the brain. It's demonstrable. You have an injury in the pelvis, and you actually lose things like reaction time — reflexes, basically — and portions of your visual field. These things return to normal when the injury is fixed.

Q: What does all this mean for weekend warriors?

A: Most people like the concept of staying in shape and equate longevity with fitness. But the weekend warriors are tremendously susceptible to these injuries because their fitness is so variable. We are seeing more and more people who have hurt themselves by engaging in occasional fitness.

Knowing if you're overdoing it is very important. There's an old term in sports: playing within yourself. It means not going to the extreme. You also want to vary what you do. Don't work on just one muscle. Do planks, where you're making all the muscles work together. And do things in a sequential way, so you're not working out one muscle vs. another too much.

Everything you do — even just getting up from the dinner table — involves a logical sequence of muscle contractions. You have to learn when you work out to have all those muscles function.