Photo Credit by Flickr, lululemon athletica

In these tough economic times, many people are tightening their belts and cutting back on spending. However, if part of that financial belt tightening includes canceling your gym membership, the resulting paunch around your waist may cause your belt to fight back a bit. Thankfully, it's entirely possible to get a good workout without a stitch of fitness equipment, and chief among the many great muscle-toning, equipment-free exercises you can do is the push-up.

Researchers from the University of Queensland in Australia found that regularly performing resistance exercises can build strength and improve overall quality of life, particularly in older people. To that end, dropping and banging out twenty is a great way to keep your body active and healthy at home, at the office, or just about anywhere you can find a 4' x 4' space to call your own.

Since most people are familiar with traditional push-ups, here are five variations to the exercise that you may want to try -- all of which cost zero dollars but make good fitness sense (sorry for the pun. I couldn't resist). Oh, and by the way, click on each of the exercises if you'd like to see a video demonstration.

1.) Plyometric Push-Ups
Very Rocky-esque move where you thrust your body upward, to the point where your hands leave the ground. Throw in a hand clap before hitting the ground and you may be ready to take on Ivan Drago.

2.) One-Armed Push-Ups
The Jack Palance at the Oscars move. Very, very difficult. Don't be discouraged if you can only do a few -- if any at all. Although, Jack Palance was about 125 years old when he did his. I'm just saying ...

3.) Spider-Man Push-Ups
That's a lot of hyphens. It's also a great way to work your chest and triceps with this climbing-type move. You can either do it while remaining in one place, or you can 'spider crawl' your way across the floor. My only suggestion is that you don't wear Spider-Man underoos while you do it, as it may get you tossed from your gym.

4.) Handstand Push-Ups
Frankly, I don't even know why I'm bothering to mention this one, since my guess is that only .0000001 percent of the world population can even do them (and, believe me, I'm not one of them!). Then again, it serves as an example of just how varied a standard exercise like the push-up can actually become. It also demonstrates the amazing potential of the human body.

5.) Leg-Raised Push-Ups
As the name indicates, this variation of the push-up involves keeping one leg raised in the air. Using this posture requires more core strength than a standard push-up, so you may want to incorporate it into your routine. Be sure to switch legs at some point to ensure that you work your body evenly.

There are dozens of other push-up variations (Hindu push-ups, Bosu push-ups, Swiss ball push-ups, breakdancing push-ups, etc.), but these five are certainly enough to get you started on your recession-proof workout.