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If you want to take your fitness and fat loss to the next level—without spending more time in the gym—then high intensity interval training (also known as HIIT) could be exactly what you're looking for.

Before getting into the details, notice that I didn’t say HIIT would be easier, just that it would take less of your time. In fact, the HIIT approach to cardio exercise is very physically demanding and isn’t for everyone. If you have any cardiovascular problems or other health concerns that limit your ability to exercise at very intense levels, or if you are relatively new to aerobic exercise or not already in good shape, HIIT is not for you—at least for now. If you have any doubts or concerns about whether it might be safe for you, check in with your medical professional before trying HIIT.

What It Is and How It Works

HIIT is a specialized form of interval training that involves short intervals of maximum intensity exercise separated by longer intervals of low to moderate intensity exercise. Because it involves briefly pushing yourself beyond the upper end of your aerobic exercise zone, it offers you several advantages that traditional steady-state exercise (where you keep your heart rate within your aerobic zone) can’t provide: HIIT trains and conditions both your anaerobic and aerobic energy systems. You train your anaerobic system with brief, all-out efforts, like when you have to push to make it up a hill, sprint the last few hundred yards of a distance race, or run and hide from your spouse after saying the wrong thing.

HIIT increases the amount of calories you burn during your exercise session and afterward because it increases the length of time it takes your body to recover from each exercise session.

HIIT causes metabolic adaptations that enable you to use more fat as fuel under a variety of conditions. This will improve your athletic endurance as well as your fat-burning potential.

HIIT appears to limit muscle loss that can occur with weight loss, in comparison to traditional steady-state cardio exercise of longer duration.

To get the benefits HIIT, you need to push yourself past the upper end of your aerobic zone and allow your body to replenish your anaerobic energy system during the recovery intervals.

The key element of HIIT that makes it different from other forms of interval training is that the high intensity intervals involve maximum effort, not simply a higher heart rate. There are many different approaches to HIIT, each involving different numbers of high and low intensity intervals, different levels of intensity during the low intensity intervals, different lengths of time for each interval, and different numbers of training sessions per week. If you want to use HIIT to improve performance for a particular sport or activity, you’ll need to tailor your training program to the specific needs and demands of your activity.

General HIIT Guidelines HIIT is designed for people whose primary concerns are boosting overall cardiovascular fitness, endurance, and fat loss, without losing the muscle mass they already have.

Before starting any HIIT program, you should be able to exercise for at least 20-30 minutes at 70-85% of your estimated maximum heart rate, without exhausting yourself or having problems.

Because HIIT is physically demanding, it’s important to gradually build up your training program so that you don’t overdo it. (The sample training schedule below will safely introduce you to HIIT over a period of eight weeks.)

Always warm up and cool down for at least five minutes before and after each HIIT session.

Work as hard as you can during the high intensity intervals, until you feel the burning sensation in your muscles indicating that you have entered your anaerobic zone. Elite athletes can usually sustain maximum intensity exercise for three to five minutes before they have to slow down and recover, so don’t expect to work longer than that.

Full recovery takes about four minutes for everyone, but you can shorten the recovery intervals if your high intensity intervals are also shorter and don’t completely exhaust your anaerobic energy system.

If you experience any chest pain or breathing difficulties during your HIIT workout, cool down immediately. (Don't just stop or else blood can pool in your extremities and lightheadedness or faintness can occur.)

If your heart rate does not drop back down to about 70% of your max during recovery intervals, you may need to shorten your work intervals and/or lengthen your recovery intervals.

HIIT (including the sample program below) is not for beginner exercisers or people with cardiovascular problems or risk factors. If you have cardiovascular problems or risk factors should NOT attempt HIIT unless your doctor has specifically cleared you for this kind of exercise.

A Sample Progressive HIIT Program

Please adhere to the general HIIT guidelines above for this program. To maximize fat loss, maintain an intensity level of 60-70% of your maximum heart rate (RPE of 5-6 on the 10-point scale) during warm up, cool down and recovery intervals.

General HIIT Guidelines HIIT is designed for people whose primary concerns are boosting overall cardiovascular fitness, endurance, and fat loss, without losing the muscle mass they already have.

Before starting any HIIT program, you should be able to exercise for at least 20-30 minutes at 70-85% of your estimated maximum heart rate, without exhausting yourself or having problems.

Because HIIT is physically demanding, it’s important to gradually build up your training program so that you don’t overdo it. (The sample training schedule below will safely introduce you to HIIT over a period of eight weeks.)

Always warm up and cool down for at least five minutes before and after each HIIT session.

Work as hard as you can during the high intensity intervals, until you feel the burning sensation in your muscles indicating that you have entered your anaerobic zone. Elite athletes can usually sustain maximum intensity exercise for three to five minutes before they have to slow down and recover, so don’t expect to work longer than that.

Full recovery takes about four minutes for everyone, but you can shorten the recovery intervals if your high intensity intervals are also shorter and don’t completely exhaust your anaerobic energy system.

If you experience any chest pain or breathing difficulties during your HIIT workout, cool down immediately. (Don't just stop or else blood can pool in your extremities and lightheadedness or faintness can occur.)

If your heart rate does not drop back down to about 70% of your max during recovery intervals, you may need to shorten your work intervals and/or lengthen your recovery intervals.

HIIT (including the sample program below) is not for beginner exercisers or people with cardiovascular problems or risk factors. If you have cardiovascular problems or risk factors should NOT attempt HIIT unless your doctor has specifically cleared you for this kind of exercise.

A Sample Progressive HIIT Program

Please adhere to the general HIIT guidelines above for this program. To maximize fat loss, maintain an intensity level of 60-70% of your maximum heart rate (RPE of 5-6 on the 10-point scale) during warm up, cool down and recovery intervals.

Week/Warm up/Work Interval(Max Intensity)/Recovery/Interval(60-70% MHR)/Repeat/Cool down/Total Workout Time

1    5 min. 1 min.                   4 min.                      2 X.   5 min.   20 min.

2    5 min. 1 min.                   4 min.                      3 X.    5 min.   25 min.

3    5 min. 1 min.                  4 min.                    4 times. 5 min. 30 min.

4    5 min. 1.5 min.               4 min.                    2 times. 5 min. 21 min.

5    5 min. 1.5 min.               4 min.                    3 times. 5 min. 26.5 min.

6    5 min. 1.5 min.               4 min.                    4 times. 5 min. 32 min.

7    5 min. 2 min.                  5 min.                    3 times. 5 min. 31 min.

8    5 min. 2 min.                  5 min.                    4 times. 5 min. 38 min.

After completing this eight-week program, you can continue working to increase the number of work intervals per session, the duration of work intervals, or both.

You can adjust this training plan to accommodate your particular needs and goals. If you find that this schedule is either too difficult or too easy for your current fitness level, you can make adjustments to the duration and/or number of high intensity intervals as necessary. For example, if you want to train yourself for very short, frequent bursts of maximum intensity activity, your program could involve sprinting for 20 seconds and jogging/walking for 60 seconds, and repeating that 15-20 times per session.

You don’t need to swap all of your aerobic exercise for HIIT to gain the benefits. A good balance, for example, might be two sessions of HIIT per week, along with 1-2 sessions of steady-state aerobic exercise. As usual, moderation is the key to long-term success, so challenge yourself—but don’t drive yourself into the ground. Get ready to see major changes in your body and your fitness level!

If you're new to exercise, overweight, or dealing with pain caused by an injury or a chronic condition like arthritis, your doctor may have recommended that you start a low-impact workout program. But what does "low impact" really mean—and can it really help you burn enough calories to lose weight and get in shape?

For an exercise to be low impact, one foot must always be in contact with the ground or your weight must be supported by water or by a machine. So you've got plenty of options when it comes to choosing a low-impact workout—and that doesn't mean it has to be easy (unless you want it to be). The things you want to avoid are high-impact moves like running, jumping, skipping rope, plyometrics and dance workouts that involve leaping.

Here are 15 low-impact workouts you can try today, ranked by calorie burn (based on a 150-pound female exercising for 30 minutes). Remember, the amount of calories you will burn during a particular fitness routine is determined by several factors including your weight, gender and intensity level.

Kettlebell Class: 600 calories per half hour

Kettlebell classes combine strength training and cardio conditioning by using special spherical weights called kettlebells that you move in a swinging motion—and they're one of the highest calorie burners around. While kettlebell workouts are considered strength training, the moves are so intense (engaging many large muscle groups) that they also elevate your heart rate to an aerobic level simultaneously. If you're new to kettlebells, you'll want to get to class early and have the teacher explain proper form and technique. Spend the first part of the class watching the instructor carefully and only join in once you understand how each motion is supposed to be completed. These classes typically involve traditional strength-training movements like squats, presses and snatches, along with kettlebell-specific moves like swings, arranged in a circuit to boost the cardio burn. Because one or both feet are usually planted on the floor when using kettlebells, the closed-chain, low-impact movements are easy on the joints when done correctly.

Lap Swimming: 363 calories per half hour

Swimming is a great, no-impact exercise that maximizes calorie burn. You may feel awkward about wearing a bathing suit in public, but if you go early in the morning, you're likely to find a small group of people who are just like you. Start with a basic freestyle stroke (or crawl) that you likely learned as a child. You'll use all your major muscles including your back, shoulders, core and glutes to propel yourself through the water. Besides a supportive swim suit, you might want to consider buying a pair of goggles to protect your eyes from the chlorine (and so you can see where you're going). Water exercise has a host of benefits; in addition to being easy on the joints, people generally work harder in water without perceiving their workouts as intense, thanks to the water's cooling effects.

Boxing Class: 287 calories per half hour

Don't worry, you won't actually have to hit someone if you take a boxing class. Instead, you'll hit punching bags and shadow box (throw punches that don't make contact with anything), which is more challenging than it sounds. Your boxing instructor will likely lead you through some traditional calisthenics (be sure to skip the jumping jacks and burpees, which are high-impact) as well as squats, wall sits and sit-ups. If you explain your needs or limitations ahead of time, a good instructor will offer you alternate moves for jumping exercises. Note that some boxing classes also involve various kicking drills. Keeping one foot on the ground at all times will keep your joints a little safer, so skip any jumping or hinge kicks.

Rowing Machine: 281 calories per half hour

Few cardio workouts work your body from head to toe—without impact—the way rowing does. If you use proper form, a rowing machine will target all your major muscle groups, as well as provide a serious cardiovascular challenge for any fitness level. You can control the intensity of the workout by increasing or decreasing the resistance of the machine and/or your own speed. To increase the calorie burn, try doing intervals of one minute of all-out effort, followed by a minute or two of lower intensity to catch your breath. Repeat the intervals 10 times to start. You can experiment with adjusting the length of time you spend at max effort versus recovery, as well as the number of intervals you complete per session.

Circuit Training: 264 calories per half hour

Circuit training adds an aerobic challenge to resistance training by alternating between different muscle-strengthening exercises with little to no rest between exercises. This elevates the heart rate and makes for a super-efficient workout. Many bootcamp-style fitness classes use circuits to burn calories and build muscles at the same time. You can design your own circuit workouts using simple equipment like dumbbells, medicine balls and even your own body weight.

Spinning: 238 calories per half hour

Although Spinning (indoor cycling) happens in a class environment, it's a very personal workout: You control everything from your speed to your resistance level, and no one but you knows just how hard you're working (or if you're taking it easy). Spinning is perfect for people who can't follow the choreography of a typical aerobics class since all you have to do is pedal a stationary bike. But if you push yourself, you certainly feel a burn in your lungs and your legs that means you're building strength and endurance. If it's your first class, make sure your instructor helps you set up your bike properly; this will help keep your joints at the proper angle and alignment so that they don't become irritated or painful as you ride.  At first, your "seat" will likely be sore after class but that should diminish over time. You can also wear padded bike shorts to ease the discomfort.

Elliptical Machine: 232 calories per half hour

Elliptical trainers get their name from the elongated oval pattern that you move your legs in while you operate them. These machines combine aspects of the treadmill, stepper, bike and cross-country skier to create a low-impact cardio workout that burns major calories. Some ellipticals include moving handlebars to offer more of a full-body workout (and greater calorie burn), but you should always avoid leaning on the handlebars whether they move or not. To get started, you can try one of these interval workouts for the elliptical.

Rollerblading: 231 calories per half hour

If you enjoyed going to the skating rink as a teenager, you might enjoy this slightly more grown-up version of skating. Rollerblading, which you can do on any paved surface, is a low-impact cardio workout that's also a lot of fun! You an increase the calorie burn by skating faster or uphill. You can also do rollerblading intervals like you would an en exercise machine like a rower or elliptical. Like biking, safe rollerblading requires you to be aware of your surroundings at all time, keeping an eye out for vehicles, pedestrians and cyclists, and have good balance to avoid falls. You'll also want to wear a helmet to protect yourself from potential head injuries. It's also common to wear knee and elbow pads. Just pretend like you're suiting up for the roller derby!

Recumbent Bike: 231 calories per half hour

Stationary bikes come in two varieties, upright and recumbent. Both provide an excellent low-impact cardio workout. But for people who are new to exercise or who suffer from low-back or hip pain, the recumbent bike offers a more supported seated position that will allow you work out longer with less discomfort. On a recumbent bike, your legs should extend almost fully, with only a small bend in the knee. The seat moves forward and backward along a track and is easy to adjust. To increase your calorie burn, you can try an interval workout for the recumbent bike.

Zumba Class: 198 calories per half hour

Cardio dance classes (including Zumba) offer a fun way to burn calories in a group fitness setting that emphasizes music and rhythmic movement. Don't worry if you can't pick up all the choreography right away; Zumba is designed to be repetitive so that you can learn it more easily. You'll have plenty of chances to practice all the moves and you'll catch on in no time. Be sure to bring a towel and a water bottle with you because you are definitely going to sweat. A typical class lasts an hour with 30- to 60-second breaks between songs. Use them to catch your breath and take a drink. Some instructors may incorporate high-impact jumping movements into their classes. Just let your instructor know ahead of time what you can and can't do so that you can take care of your joints.

Ballroom Dancing or Square Dancing: 182 calories per half hour

Have a good time while you burn major calories—without setting foot in the gym. Your local dance studio probably offers a variety of dance classes and lessons. You can find classes on everything from classic ballroom to swing to square dancing. Not only does dancing burn calories, the social aspect of dance reduces stress, depression and loneliness. If you don't have a partner, you can likely find someone else to pair with in your class.

Walking (15-minute mile or 4 miles per hour): 148 calories per half hour

Walking is the ultimate low-impact cardio workout. Just throw on a decent pair of athletic shoes and step right outside your own front door. But you need to move quickly to get the full cardio benefit of walking. You can add an app to your phone to make sure you're walking fast enough and keep track of your distance. Keep your elbows bent and pump your arms to help increase your speed. To burn more calories, try walking uphill. Be sure to keep your knees bent while going back down in order to absorb some of the extra impact. You can also add intervals to your walks to burn even more calories.

Power Yoga (Vinyasa or Ashtanga): 139 calories per half hour

While not all forms of yoga provide a good cardio workout, power yoga (which involves continuous movement from pose to pose) can bring your heart rate up, burn calories and build strength and flexibility. Look for classes that are described as vinyasa, Ashtanga, power or flow for those benefits. If you're new to yoga, you'll want to take a few beginner classes to learn the proper form and how to safely move from one pose to another. (Also, keep in mind that just because "hot" yoga make you sweat more, doesn't mean that it's burning more calories.) Some styles of power yoga involve light jumps (such as from plank to forward bend or from forward fold to plank), but you can always modify by stepping in and out of poses instead of jumping to protect your joints.

Water Aerobics: 132 calories per half hour

There are lots of ways to move your workout to the water, but water aerobics classes are easy to find at large fitness centers that have pools—and even at your local swimming pool during the summer months. Some classes will be more suited to new exercisers, older adults or people with injuries, so be sure to ask which class is right for your needs. If you find you really enjoy this type of workout, you might want to invest in a pair of water shoes to give yourself better traction on the pool deck.

Rebounding (Trampoline Jumping): 111 calories per half hour

Even though it involves jumping and both your feet will leave its surface simultaneously, rebounding or trampoline jumping is still considered a low-impact workout because the trampoline absorbs most of the shock (whereas a hard surface would not). Mini-trampolines are affordable and easy to use outdoors, or in a basement or room with a high enough ceiling and a sturdy floor. You can find DVDs with different fitness routines or you can simply jog in place. You can even do interval training on a trampoline, moving between fast jogging and marching in place. For many people with bad knees, hips or ankles, trampoline workouts offer the higher intensity workout they crave without the jarring impact of running or traditional exercise.

Beginning an exercise program can be very overwhelming-- even painful if you aren’t careful. Warming your body up prior to exercise is very important for your health (and safety) and will also help you enjoy your workouts more. Warming up for 5-10 minutes will raise your body temperature and prepare your cardiovascular, respiratory, and nervous systems for the demands of exercise by slowly increasing the blood circulation to and from your heart and muscles.

Warming up helps your connective tissues better handle the stress of exercise, decreasing your chance of injury. Connective tissue is similar to hard plastic; if you don’t warm-up plastic it won’t be flexible, and is much more likely to "break."

Proper warm ups (and cool downs) also help reduce the severity of soreness in the next day or two following your workout. The increased blood flow helps deliver more oxygen to the muscles and gets rid of the waste products that contribute to soreness. Increased blood flow also helps bring more fuel to your body, resulting in better performance.

Warm up with a low-impact exercise at a slower, more comfortable pace than your actual workout. Warm up exercises like biking, an elliptical machine, walking, or rowing allow your body to warm up with limited stress to your joints.

Another reason for soreness is trying to do too much too soon. Don’t try to make up for lost time. Start out with a few exercises and slowly progress. Your body will gradually adapt to the increased stress. If you are starting resistance training for the first time, try picking 1-2 exercises for each area of the body - the upper body, lower body and core. Also take into consideration the anterior (front) and posterior (back) parts of the body. For example, if you pick two core exercises, you might try bicycle crunch for the abdominals (front of the body) and lumbar extension for the lower back (posterior part of the body).

If you are a beginner to aerobic training, start out with something like walking that raises your heart rate a little bit, nothing that will get you too out of breath. Try doing this for 10 minutes the first few times you exercise, slowly progressing the duration of the workout. If you've increased the time to a point where you can handle 30 minutes at that pace, start building a little more intensity. For example, you could attempt 2 or 3 days of 30 minutes each at your initial pace, followed by a 10-minute day at an increased intensity.

Another area of frustration for the beginner is energy level. Most people expect to exercise the first few weeks and experience a shot of energy. In actuality, the opposite often occurs. Your body isn’t used to the added stress, which causes you to feel fatigued and even drained, especially if you overdo it. Don’t get discouraged; it’s natural to feel this way until your body adapts. As your body acclimates itself, your cardiovascular system will become more conditioned, causing you to have more energy and focus throughout the day. Your efforts will pay off.

Overexertion will trigger stiffness and soreness, causing many people to give up on exercise completely. If you do overdo it, there are a few things you can do to feel better. Exercise actually breaks your muscles down – sleep, nutrition, and hydration play a vital role in their recovery. Proper rest, refueling your body with healthy food, and drinking plenty of water will help you recover much more quickly. In the days that follow, doing a low impact exercise at a low to moderate intensity and stretching will deliver more oxygen and blood to help clean out the waste and bring more nutrients to your muscles.

Your body loses a large quantity of water when you work out, so it is very important to drink more water as you exercise. Active people should drink at least 10-12 eight-ounce cups a day, throughout the day, taking extra care to rehydrate during the workout. This will keep your joints moving fluidly and flush out the toxins that might be building up in your muscles. Headaches, stiffness, and cramping are all results of dehydration.

There's a lot of free advice about physical activity out there these days − some reliable, some not. It's easy to fall into the trap: A friend gives you an activity tip, and then you pass it on to several buddies you know. One day, you're at your weekly yoga class, and sure enough, you hear the same tip repeated, so you figure it must be true. When you're unsure, the important thing is to ask a qualified fitness professional for advice. In the meantime, knowing the difference between fact and fiction will keep you healthy, injury-free, and on track to meeting your physical activity goals. Here are some myths that need some challenging:

Myth #1: An aerobic workout will boost your calorie burn for hours after you stop working out.

False: Don't confuse calorie burn with metabolism. While your metabolism will continue to rev at a slightly higher rate after you finish an aerobic workout, the amount of calorie burn is not statistically significant. In fact, you'll only use up about 20 extra calories for the rest of the day. While there's a little bit more of a metabolic boost after strength training, it's still negligible. In other words, don't use the fact that you worked out to eat more.

Myth #2: If you're not working up a sweat, you're not exercising hard enough.

False: Sweating or perspiring is not necessarily an indicator of exertion. Perspiring is your body's way of cooling itself. It's possible to burn a significant number of calories without breaking a sweat.

Myth #3: Strength training will make me "bulk up."

False: Gaining muscle mass is something you have to work very hard at to achieve, male or female. Women tend to avoid weight training because they don't want to look bulked up. However, strength training is a critical element to maintaining a healthy weight and strengthening your body. What we know is that the average woman doesn't typically gain bulk from strength training because she doesn't have the amount of hormones necessary to build massive amounts of muscle.

Myth #4: Machines are a safer way to weight train because you're doing it right every time.

False: Although it may seem as if an exercise machine automatically puts your body in the right position and helps you do all the movements correctly, that's only true if the machine is properly adjusted for your weight and height. Before using any equipment or performing any exercise, you should ensure you understand the full mechanics of the movement and the proper endpoints. Unless you have a coach or a trainer to figure out what is the right setting for you, you can make just as many mistakes in form and function and have just as high a risk of injury on a machine as if you work out with free weights or do any other type of workout.

Myth #5: When it comes to physical activity, you've got to feel some pain if you're going to gain any benefits.

False: While you should expect to have some degree of stiffness or soreness a day or two after physical activity, that's very different from feeling pain while you are working out. A fitness activity should not hurt while you are doing it, and if it does, then either you are doing it incorrectly, or you already have an injury. As for "working through the pain," experts advise against it. If it hurts, stop, rest, and see if the pain goes away. If it doesn't go away, or if it begins again or increases after you start an activity, see a doctor.

Myth #6: If I can't be active often enough, I might as well not even do it.

False: Remember: Any activity is better than no activity, even if it's only a 15-minute walk. Being physically active is important for heart health and is proven to reduce stress. So, even if you can't make it to the gym or yoga class, you can always do something active each day. Taking a walk, climbing the stairs instead of hopping on the elevator or escalator all count!

Myth #7: You can take weight off of specific body parts by doing exercises that target those areas.

False: This concept is called "spot training" and unfortunately, it doesn't target fatty areas. When you lose weight, your body predetermines which fat stores it will use. For example, doing sit-ups will strengthen your abs but will not take the fat off of your stomach. Similarly, an activity like running burns fat all over your body, not just your legs. You can, however, complement a balanced physical activity program with a selection of weight training exercises to gradually lose weight and tone your body.

Myth #8: You will burn more fat if you exercise longer at a lower intensity.

False: The most important factor in physical activity and weight control is not the percentage of fat calories burned, but the total calories burned during the activity. The faster you walk, bike or swim, for example, the more calories you use per minute. You may still be burning more calories (and likely will be) from fat but the relative percentage of the source will be altered. So high intensity exercises will likely burn more calories total, as well as attributable energy to fat metabolism.

Myth #9: I can eat what I want because my workout will keep the weight off.

False: If you tend to eat large-portion meals such as 340 g/12 oz steaks, two to three cups of pasta, three to four slices of pizza, or high-calorie foods such as chocolate shakes and fries on a regular basis, no manner of workout will burn enough of those calories off to keep your weight in check. A healthy way to achieve and maintain a healthy weight is to combine healthy eating with regular physical activity – they go hand in hand. Need help? Try our Healthy Weights Action Plan.

Myth #10: The best time to be active is early in the morning.

False: There is no one optimal time to be active. The best time is the time that appeals to you and fits into your schedule on a regular basis. Some folks love to jump-start their day with a morning workout, while others swear that physical activity at the end of the work day is a great way to boost energy for the evening and eliminate stress. Choose whatever works for you.

Before starting any activity program, be sure to talk to your doctor or other healthcare professional.

This physical activity column was written by a certified personal trainer and fitness instructor and reviewed by a specialist in kinesiology.

Provided by Heart and Stroke Foundation.