You may still be your own worst enemy when it comes to getting into shape, but you also are your own best piece of gym equipment.

That’s right, you’re definitely the dumbbell that tolls for thee. In fact, you’re really all you’ll ever need to create the body you deserve.

There are about 40 million health-club members out there paying billions in fees, and their ranks swell every spring as that perennial I’m-getting-in-shape-and-this-time-I-really-mean-it resolve kicks in. But while you might be a tad pudgier than last year, exercise is just as time-consuming and inconvenient as it ever was.

And we can’t all be Phil Black, who spent many a fun-filled evening playing the push-up game, PUG for short, with his fellow Yalies. It was a simple idea: Pick a card and do that number of push-ups, and the person who can make it through the most cards wins.

Now Black, a former Navy SEAL, has applied that concept to his FitDeck, a pack of 56 playing cards that features body resistance exercises like crunches, jumping jacks, dips and variations on the granddaddy of ’em all, the much-maligned and highly underrated push-up.

“With push-ups, it’s fairly easy to start at a low beginner level — you can get on your knees, and it’s a relatively safe range of motion,” Black says. “I have beginners who are doing half of one modified push-up. As you progress over time, you can move to variations that work a wider range of muscles.”

Black’s FitDeck cards, which he says can be shuffled into more than 3 million workouts, are portable and adaptable to any fitness level. College sports teams might blast through the entire deck in 33 minutes every other day, while some business types do a card an hour at the office.

Older couples could do an exercise every time they come to a lamppost on their daily walk, Black says, while students get a kick out of picking a card to demonstrate to their gym class.

Body resistance exercises can be done at a slower pace for a strength/toning kind of workout or faster for more of an aerobic workout. Either way, you get something you can’t get from the limited, muscle-specific movement of a weight machine.

“The thing missing is all those stabilizer muscles — around the shoulders, chest, lower back, abs. All those things are taking a pass when you’re sitting on a machine,” Black says.

Resistance exercise increases stability, balance, overall body awareness and coordination. It’s called “functional fitness,” the kind of conditioning you need to drag your children out of bed in the morning or juggle four bags of groceries while digging in your pocket for your house keys because your children have the TV turned up so loud they can’t hear you kicking the door with your foot.

The push-up variations I demonstrate here can strengthen your core and improve your functional fitness, so modify them to suit your fitness level and give them a go.

How-to guide

Beginners
These are tough, so modify each exercise by doing them either on your knees or standing with your hands against a wall and your feet 12 to 24 inches away. Do what you can do with good form. Don't get discouraged -- you will get stronger.

• Unless otherwise specified, do all these push-ups from a strong plank position by maintaining a straight line from your head to your heels.
• Hands should be under shoulders, and feet should be shoulder-width apart.
• Pull in your stomach — think of wearing a tight belt. Use those back and ab muscles to avoid dropping your hips.
• Tuck your butt under so it lines up with your body and doesn’t stick up.
• Remember to breathe — inhale on the way down and exhale on the way up.

Push-up plank extension

Works: Back, abs, shoulders, chest, arms and glutes.

How to: Start in a plank position with feet slightly wider than hip distance apart. Lower your body until your chest is close to the ground. As you near the top of the push-up, rotate to one side until your arm is extended above you. Stabilize yourself, then rotate back into the plank position for the next push-up. Alternate sides.

Three-point push-up

Variation: To make this easier, spread your feet wider for more support or do the exercise from your knees, rotating onto your side with your knees bent at a 90-degree angle. To make it tougher, bring your feet closer together, or line them up on top of each other.

Three-point push-up

Works: Back, abs, shoulders, chest, arms and glutes.

How to: Start in a push-up position. Lift one leg up and to the side; keep it straight. Lower your body, return to the starting position. Do an entire set on one side, then switch.

Staggered push-up

Variation: To make it tougher, take leg farther to the side. To make it easier, just lift the leg without taking it to the side.

Staggered push-up

Works: Back, abs, chest, shoulders, arms and glutes.

How to: Put one hand near your stomach and the other near the top of your head. Lower and return to start position. Do one set on one side, then switch arms.

Variation: To make this tougher, push off the ground as you come up and switch arms in the air.

Intermediate/advanced

Do two to three sets of eight to 12 on knees or toes. To make any exercise harder, lower very slowly to a count of 10.