“The harder you work right now, the faster your body’s going to change,” says Jillian Michaels in her brand new, game-changing Seven-Minute, Seven-Day Workout Challenge , designed exclusively for Yahoo Life readers. The iconic trainer designed the program to suit busy people of all fitness levels, with an exclusive reward for you, too!Today’s beginner-friendly challenge is all about High-Intensity Interval Training, otherwise known as HIIT. HIIT workouts are major fat-burners, because they require you to exert yourself to the max for short intervals—sort of like a series of sprints instead of a marathon. Putting intense stress on your body for brief spurts followed by brief recovery periods forces your system to adapt fast and turbo charges its calorie-burning powers.“Don’t get mad at me!” Michaels jokes about the intensity of today’s seven-minute workout, which squeezes in 10 high-intensity circuits. “I am looking out for you, because HIIT training burns a crazy amount of calories, and it gets you fitter a heck of a lot faster.”The goal of HIIT training is to reach close to 100 percent of your maximum heart rate (MHR) and then recover at about 60 to 70 percent. You don’t just burn calories during this HIIT challenge—your body continues to melt fat long after it’s over. Keep challenging yourself:This leg-chiseling challenge is just the beginning. Michael’s is offering Yahoo Life readers an exclusive deal on her fitness app, which is stocked with a slew of effective 7-day workouts. Enjoy a free 7-day trial and a 3-month subscription for just $19.99 (usual price is $44.97), and 12-months for $59.99 (usual price is $179.88). (Yahoo Life may receive a share from purchases made via links on this page. Pricing and availability are subject to change.)Ready for your day-six challenge—today’s seven-minute HIIT workout?Watch it at the top of this article. It’s a total-body HIIT program designed to jumpstart your whole system with 10 dynamic circuits you complete in about 20 seconds seconds each. “These very dynamic, explosive exercises burn a lot of calories while we’re doing them but also a lot of calories after the workout is over,” says Michaels. There are 12 body-tightening moves packed into this 7-minute workout. Here’s a preview of 3 of them — watch the video for the rest!Story continuesBoost your metabolism with BurpeesBurpees have a reputations for being tough—but that’s why they work. (Photo: Courtesy of Jillian MIchaels)Is there any exercise more dreaded and more effective than the notorious burpee? Michaels is going for intense, and this aerobic power move is designed to get your heart pumping and your calories burning. “Explode off the ground,” Michaels says as she shows you how smoothly transition from the traditional push-up posture into a jumping upright position.Burn fat fast and fight flabby arms with Speed Bag By just using your arms, you’re knocking out tons of calories and toning your shoulders and biceps. (Photo: Courtesy of Jillian Michaels)Ever marvel at the chiseled physiques of professional boxers? Speed bag training is one of the main tools in their fitness arsenal. Punching at an invisible speed bag per Michaels’ coaching burns an incredible amount of calories while also engaging your shoulders and biceps and targeting soft, flabby upper arms. “I get it. In the moment, sometimes exercise is not fun,” Michaels says. “But the results? That’s what you’re fighting for.”Bolster bone density and get your heart pumping with Speed RopeJumping rope is even simpler when you don’t need an actual rope—but it still has the same intense toning effect. (Photo: Courtesy of Jillian Michaels)One of the most simple ways to boost your heart rate and metabolism is with a good old-fashioned jump rope—an athlete favorite. And with Michaels’ Speed Rope challenge, you don’t even need a rope! For 20 seconds, “synergize your upper and lower body as if you’re really jumping rope,” says Michaels, “and focus on your breathing. This exercise should be done fast and with your feet just barely coming off the ground. It not only burns fat but improves coordination, helps bone density, and strengthens your legs. Just getting started? Catch the rest of our Seven-Minute, Seven-Day Workout Challenge with Jillian Michaels:If you’re out of shape or new to aerobics and strength training, then you’re a perfect fit for Michaels’ beginner-friendly, seven-day workout challenge. The custom program combines a series of High-Intensity Interval (HIIT) and total-body workouts with routines meant to tone abs and legs—and, of course, meditation and recovery routines. Each day introduces an easy-to-follow seven-minute workout—and Micheals’ signature no-nonsense coaching style will keep you right on track.Get serious about your fitness with a subscription to the Jillian Michaels Fitness App. For a limited time only, Yahoo readers can enjoy a free 7-day trial and a 3-month subscription for just $19.99 (usual price is $44.97), and 12-months for $59.99 (usual price is $179.88).