We see it all the time at the gym: You stand there staring at the machines trying to figure out which one will be the least boring and give you the biggest bang for your exercise efforts. Or you just climb on and maintain the same pace until you can’t stand it another minute. No wonder so many of us dread going to the gym! We all need to put the excitement— and results—back into our cardio sessions, so we asked top trainers for their most effective routines to blast calories, boost your metabolism, sculpt muscle, and free you from that “When will it end?” mind-set. The secret: Don’t just change things up every month, change them during every session.

Do five or six of the following workouts in the next seven days (while watching what you eat) and you can say so long to a pound of flab. And who knows, maybe we’ll even catch you smiling the next time you hit the treadmill!

THREE-WAY FAT BURNER

TRAINER Wendy Larkin, personal training manager, Crunch, San Francisco

WHAT YOU’LL NEED A jump rope, group cycling bike, and treadmill

CALORIES BURNED 450–500

“Alternating between different types of exercises allows you to push yourself to your limits—then briefly recover and do it again on the next piece of equipment—while using all your muscles,” says Larkin. “It’s a with both feet, then gradually start alternating feet. If you can’t do 10 minutes, jump for 10 revolutions, then rest for 15 seconds. Add 10 revolutions at a time until you get to 10 minutes. When you’re cycling, begin with just enough resistance to feel a slight pull on the wheel, then increase it from there. During the standing portions, keep your butt over the seat and your legs over the pedals.

LOWER-BODY SCULPTOR

TRAINER Tracey Staehle, creator of the Walking Strong workout DVD (fitbytracey.com)

WHAT YOU’LL NEED A treadmill

CALORIES BURNED 200*

This “lofty” hill routine makes your lower body work extra hard, and the more you engage those large muscle groups, the more calories you burn. “Plus, things are changing frequently, so you have to stay focused—you can’t zone out,” says Staehle. “You’re constantly being confronted with a challenge, whether it’s speed-walking up a steep hill, jogging on an incline, or doing walking lunges.”

*CALORIE BURN IS BASED ON A 145-POUND WOMAN.

MEGA CALORIE BLASTER

TRAINER Paul Frediani, certifi ed USA Triathlon coach, New York City

WHAT YOU’LL NEED A watch with a second hand or a stopwatch

CALORIES BURNED 300–600

Runners and triathletes practice something called “tempo training”—maintaining an intensity that’s challenging but not so hard that you feel like you’re about to keel over. “It’s one of the best ways to improve your stamina, speed, and fi tness level,” says Frediani. Plus, you’re working at a point— about 80 percent of your max heart rate (go to shape.com/heartrate to calculate yours)—that optimizes both your fat and calorie burn . It takes practice to maintain this level for a long time, but this routine, which incorporates mini speed bursts, will help you nail it. Do it indoors or out while biking, running, or speed-walking. (You can also adapt it to almost any other cardio machine, from the rower to the elliptical.)

SLIMMING CLIMB

TRAINER Nicki Anderson, owner, Reality Fitness, Naperville, Illinois

WHAT YOU’LL NEED Any piece of cardio equipment that allows you to adjust the resistance or incline

CALORIES BURNED 260–600

“This program takes you out of your comfort zone by constantly raising the incline for the first third of the routine,” says Anderson. “It’s such an effective workout, especially for your legs and butt, which have to power you upward.” Try to maintain the same speed even as the incline builds, and don’t lean forward too much (if you have to hold on, use a very light grip).

DO-ANYWHERE INTERVALS

TRAINER Cat Manturuk, the Sports Center at Chelsea Piers, New York City

WHAT YOU’LL NEED A watch with a second hand or a stopwatch

CALORIES BURNED 130–300

“I tell all my clients they need to incorporate intervals—it’s one of the best ways to burn fat and improve your fitness level quickly,” says Manturuk. We’re all for speeding up results, so do this workout on any machine, or walk, run, or bike outside (if you’re walking or running, take longer steps when the plan calls for increasing the incline or resistance, or scope out some hills in your neighborhood ahead of time). “Instead of huffing and puffing, make your breathing more rhythmic by inhaling and exhaling for the same length of time,” adds Manturuk. “You’ll get more oxygen to your lungs while keeping your body relaxed, so you’ll be able to power through each burst.”

ELLIPTICAL REFRESHER COURSE

TRAINER Geralyn Coopersmith, senior national manager, Equinox Fitness Training Institute, New York City

WHAT YOU’LL NEED An elliptical machine

CALORIES BURNED 250

“The elliptical offers an excellent low-impact workout that burns serious calories, but it doesn’t feel like you’re working quite as hard as you do on some other types of equipment,” says Coopersmith. Since these no-impact machines vary by manufacturer in their levels of resistance and ramp incline, we’ve kept this workout somewhat generic; follow the RPE and your machine’s options to keep you in the right zone. “The higher the ramp, the more calories you’ll burn,” she adds.

You can increase that tally by using the arm levers and really pushing and pulling with each stride. But if you don’t feel like using them or you’re only holding on while the levers do all the work, don’t sweat it. Just use a natural arm motion: Pump your arms in opposition to your legs, which challenges your core too.