"Squeeze your stomach!" or "Push out your shoulders!" or "Keep your legs straight!" are all common forms of the general command, "Stay tight!" All gymnasts will hear some version of this many times in the sport, and even seasoned veterans need a reminder now and again.
But have you ever wondered what the reason behind all this is -- other than just the fact that it makes your gymnastics better and to avoid injury? There's a bit of physics involved, but if you take a little time to understand the mechanics, there's a good chance that it will help out in the long run.
No matter what apparatus you're on, there's almost always the need to keep a tight body position. This week, we'll focus on using a tight body to maximize the power in tumbling and jumps, and in the following weeks, we'll see how it applies also to twisting and turning, and keeping good balance.
Notice that most of the equipment in gymnastics is designed to give you lots of power in your tricks. The floor has an underlying layer of springs, the bars have a flexible metal rod in the wood, and even most of the modern beams have a small spring quality to them. Gymnastics has, over the years, co-evolved with the equipment. Imagine seeing someone do a Shushunova or a double layout on a floor with no springs ... it would be extremely difficult, right? Luckily for most of us, spring-enhanced equipment is readily accessible.
First, let's take a look at how a spring works. A good spring will take the energy transferred to compressing it and return almost all of it back from the direction it came. But because you're not jumping directly on a spring, but rather a surface covering the spring, you only get a portion of the total energy. The good news is, it's enough to give you the power you need in today's gymnastics.
Now, here's where you come in. You can think of your body as a spring as well -- more specifically, your muscles are the springs (although the info at this link is applied to dancers, but can work for gymnasts as well). Imagine that your body can take on two forms of springs: a Slinky, and a firm spring (like the ones in the springboard). When your body is loose, it acts like a Slinky -- it only absorbs energy. It is limp and doesn't return any energy back out. Now, think of your body as the firm spring when your body is tight and your muscles are squeezed. When you make impact with the floor (or springboard or beam), your muscles "compress" like a spring, transferring that energy into the springs of the floor. And when those springs expand again, that energy transfers back to your body and "expands" those "springs" to propel you into the air.
Here's another way to think about it:
When the potential energy stored in the compressed spring transfers out of it as it expands back to its original position, that energy is passed into the motion of your body. Ask yourself, would your body bounce higher if your body moved as one rigid object, or if it was loose? Try this quick visualization/experiment: gently hold a pencil (or pen, or other solid object) vertically in one hand. With your other hand, push up on it from underneath. It moves upward as a whole and quite easily, right? Now, find a soft (pliable) object, like a tissue, and do the same thing. Rather than the entire tissue moving as a whole, it starts to bend at one point. This is a weak point, and your body will behave very much the same way (although not as drastic) if you are loose.
When a part of your body bends loosely as a force is applied to it, that energy is in a way lost -- at least in terms of what it could potentially do for you. So, say you have your arms bent in the middle of a flip-flop. The energy of your body weight coming down onto your hands will have nothing to stop it if from continuing down towards the floor. And you will find yourself landing hard on your head. On the other hand, if your arms are straight and tight, the muscles and joints in your body can act like a spring and keep the transfer of energy moving in the right path.
Likewise, this is why you bend your legs when you want to stick a landing. You want your weight to come down, but not back up. Therefore, bending your legs causes your body to absorb the downward momentum and bring you to a stop. Note that this doesn't mean to relax your muscles either. If you did, you would continue falling to the ground.
Common sites of "weakness" where your body can bend and absorb energy are the arms, shoulders, midsection (stomach and back muscles), hips, and knees. Keep them in check now and again to see if you can't improve performance by tightening up accordingly.
Just a few of the many
things you can do to check how tight your body is: