The only 4 exercises you really need

I do my best to exercise 5 to 6 times a week, but there are days when I simply cannot pull myself out of bed in time to sweat before work, or when I'm traveling and my normal routine is completely thrown off track. Instead of completely scrapping my routine, I’ll try and squeeze in a few bodyweight exercises—namely squats, planks, chair dips and pushups—throughout the day.

These four moves give you a full-body toning and strength session in just a few minutes. I find that they also boost my energy and mood on days when I'm feeling tired, stressed or overwhelmed, too. (Are you tired, too? See 11 Fast Fixes For Energy.)

Many other fitness experts agree: "I like these moves because they use bodyweight for resistance," says Alice Burron, 45, a mother of four and a personal trainer in Cheyenne, Wyoming. "That means they're simple but still challenging, convenient, and inexpensive—and they work."

To sneak in one set of all of these exercises would only take you about 5 minutes. To build muscle and burn calories, try to do three 5-minute mini workouts with these moves in one day. All in all, you’re only working out for 15 minutes.

Personal trainer and co-author of Thin in 10 Weight-Loss Plan Liz Neporent agrees: "When you do these four moves you're hitting all of your major muscle groups effectively. And they're efficient because you don't waste time isolating one muscle group at a time, as some exercises tend to do, and instead work several major muscle groups in tandem.

These integrated muscle movements use the body exactly as intended— the way you typically use them in daily activities and when you do sports and fitness activities. This helps you perform better and prevent injuries." (If you're injured, check out How to Exercise When You're Hurting.)

Want to give it a try? Follow this workout from Burron and Neporent. Start with 1 set of 8 to 15 reps of each move (unless otherwise noted), and gradually build to 2 or 3 sets.

Must-Do Move #1: Chair Dips Great for toning your triceps and core Sit on the edge of a sturdy, stable chair with legs together, knees bent and feet flat on floor a few feet in front of chair. Place your hands about six inches apart, and firmly grip the edges of the chair. Slide your butt just off the front of the chair so that your upper body is pointing straight down.

Keep your abdominals pulled in and your head centered between your shoulders. Bend your elbows and lower your body in a straight line. When your upper arms are parallel to the floor, push yourself back up, being careful not to lock elbows. Repeat. (Want more arms? Here's how to Tone Your Arms—In 10 Minutes!) Make it easier: Keep feet close to the chair and the dip slow, controlled, and shallow.

Add a challenge: If you’re intermediate, position feet a little farther from chair, and deepen your dip. If you’re advanced, straighten your legs completely, and place heels on floor, or place one or both feet on another chair, bench or exercise ball. Perform deep but controlled dips.

Must-Do Move #2: Push-ups Great for toning your chest, shoulders, triceps, back, hips, and abs Start in a basic push-up position with hands directly beneath shoulders and body in a straight line. Bend elbows out to sides and lower body almost to floor (or as far as you can). Keep abs tight and body in a line. Hold for 1 second, then push back up. Repeat.

Make it easier: If you’re a beginner, do push-ups on knees. Keep the movement shallow and controlled. Still too challenging? Start with a push-up on the wall, progressing to the floor as you become stronger. Add a challenge: If you’re advanced, try lifting one leg off the floor as you do each push-up. (Need a visual? Watch how to Master Push-Ups at Any Level.)

Must-Do Move #3: Squats Great for toning your glutes, hamstrings and quads Stand with feet parallel and hip-width apart. Bend your knees and lower your body into a squat position, as if you are sitting back into an imaginary chair, keeping knees behind toes. Stop when your knees are at 90 degrees. Slowly press through your heels and squeeze your glutes as you return to standing.

Make it easier: Don’t bend knees as deeply Add a challenge: Add weights, do a single-legged squat, or perform squats on an unstable surface, like a balance disc or Bosu ball. To incorporate cardio, do squat jumps.

Must-Do Move #4: Plank Great for toning your abs, back, chest, forearms and shoulders To come into plank pose, hold a push-up position, weight on balls of feet and hands, wrists directly below shoulders, arms straight, and body in line from head to heels. Hold for as long as you can, working up to 1 minute. That’s 1 rep. Do 2 or 3 reps.

Make it easier: Instead of being on hands, lower yourself to your forearms. Add a challenge: Raise 1 leg off the floor and hold for 30 seconds. Switch legs and hold for another 30 seconds to complete 1 rep. To add variety, try side plank: Lie on your right side with your legs straight, and feet stacked, right hand directly under right shoulder.

Lift hips off floor and raise left arm to sky, keeping left hand directly over left shoulder. Hold for 30 to 60 seconds. Switch sides and repeat to complete 1 rep.