You see it all the time at the gym -- people sitting on the exercise bikes, the weight machines or even while performing certain free-weight exercises. Many exercises call for you to be seated, but did you know that those seated exercises could actually be less effective than the exercises involving more standing and moving?

If you study the human body, you'll see that it wasn't designed to be still for hours on end. Many of us work desk jobs, which already involve plenty of hours of sitting. If you go to the gym and spend more time sitting, you could end up causing all kinds of health problems.

What Happens When You Spend A Lot Of Time Sitting?

• Your butt muscles lengthen, and they don't work quite as well as they should.
• Your front hip muscles tighten, and they may even shorten.
• Your lower back's natural arch will either round off or become flat -- both very bad for your health.
• Your shoulders hunch forward, your chest muscles shorten and your upper back tends to round forward.

All of these things go against your natural posture, which is why it's advised that you stand up and walk around regularly if you sit at your day job.

But now you're at the gym, so why are you continuing this degradation of your posture by sitting down? The more time you spend sitting -- both at the gym and at work -- the greater the wear and tear on your body.

Plus, when you sit down, you aren't forcing your core or your glutes to work as hard as they could. Take the overhead shoulder press as an example:

• When you perform this exercise while standing up, your legs and abs have to work with your lower back, upper back, shoulders and arms to keep your balance.
• When you perform this exercise while sitting down, you take the weight off your legs, reduce core strain by leaning back against the chair, and only your arms and shoulders do the work.

You see how much more effective exercises are when you stand up? Even if the workouts aren't targeting your lower body and core, just doing the exercises in the standing position will naturally work the muscles. It will be a minimal workout that you will hardly feel, but it will be a workout nonetheless.

When you sit, your body doesn't need to activate your core, glutes or leg muscles. The chair is doing all the work, so your glutes don't get worked at all. Too much of this, and your brain may "forget" how to work your glute muscles, which could lead to muscle catabolism. If you want a nice rear end, that's the worst thing that could happen!

Another downside to sitting at the gym: the exercises you do compress your spine. If you sit, you place greater strain on your spine, but seeing as your back muscles are relaxed, the pressure is all placed on the spine itself. This increases your risk of injury drastically!

Replace Seated Exercises With Standing Ones

• Do standing overhead dumbbell press instead of seated dumbbell presses.
• Hit the elliptical machine or treadmill instead of the stationary bike.
• Do standing curls instead of seated curls.

If you want to make your workouts as effective as possible, do them on your feet. The less time you spend sitting down at the gym, the better!