- High Intensity Interval Training (HIIT) Definition
- Interval Training Sessions
- Heart Rate
- Where to Work Out
- How Often
- Warnings & Precautions
- Burning Calories & Fat
- Losing Weight
- Circuit Training
- Warming Up
- Cooling Down
Are you pressed for time? Are you interested in improving your aerobic capacity and exercise performance in less than one-fifth the time of traditional endurance training? If so, then interval training is just what the exercise physiologist ordered. Indeed, research proves that you can improve your endurance and recovery from intense bouts of exercise with just one hour per week of interval training compared with five hours per week of traditional endurance training.
Athletes know the magic of intervals. They use them all the time to improve their performance, and they know that intervals help speed up recovery so they can get going quickly after a blast of energy (like a sprint). In this article, we will review what interval training is, describe the benefits and the studies that prove it works, and I'll show you how to design an interval-training program.
There are several advantages to interval training:
- Fitness and performance improve quickly with interval training, typically in just a few weeks. I've known athletes who reported an improvement in speed after just two interval workouts.
- Recovery time improves with interval training. Recovery is critical for athletes in sports like tennis, basketball, soccer or hockey, where the sport demands continuous stops and starts, or an endurance bike ride or road race where you hit hills and need to catch up quickly at the top in order to keep your pace. You'd never perform well if you sprinted all-out or climbed a hill and then needed two minutes to recover (also known as sucking wind). It would never work.
- Research confirms that interval training improves fitness similarly to traditional aerobic training in much less time.
- In one study comparing interval training to traditional training, subjects increased their fitness and the activity of many of enzymes that contribute to using oxygen efficiently with two and a half hours of intervals over two weeks compared with 10 and a half hours of traditional endurance training over the same time period.
- In another study comparing the two methods of training, subjects increased the use of stored glucose (glycogen) and fat by the same amount after five days a week of training for six weeks, but the interval subjects trained only one and a half hours per week compared with four and a half hours per week for the endurance subjects.
- Some interval training schedules can be too rigorous. In a study of subjects who did interval training every day for two weeks, the oxygen capacity increased, but anaerobic capacity did not. The investigators suggested that this was due to overtraining and exhaustion from daily interval sessions.
- To reduce the effects of overtraining, investigators had subjects perform six, two and half-minute interval sessions over a two-week period, with one to two days of rest in between sessions, to promote recovery. Interval sessions consisted of four to seven "all-out" 30-second sprints on a stationary bike with a total of four minutes of recovery. This training regimen increased fat burning and doubled endurance capacity with just 15 minutes of intense cycling over a two-week period!
Interval sessions are tough, and you must "dig down deep" to find the motivation to push yourself, but the payoff is big. Find a training partner if you need help pushing yourself. Commitment to a partner will get you out the door when you don't feel like it, and a little healthy competition never hurts to increase performance.
What is a high intensity interval training (HIIT) workout?
Interval training is a method of training where you increase and decrease the intensity of your workout between aerobic and anaerobic training. Interval training in Sweden, where some say it originated, is known as fartlek training (Swedish for "speed play").
The protocol for interval training is to push your body past the aerobic threshold for a few moments and then return to your aerobic conditioning level with the objective of improving your performance (speed, strength, and endurance).
The aerobic threshold is the intensity where your body switches from burning a greater percentage of fat to a greater percentage of carbohydrate and is generally 85% of your maximum heart rate (train below 85% and it's considered aerobic exercise; train above 85% and it is considered anaerobic exercise).
How are interval-training sessions designed?
Interval training can be personalized to the individual in almost every facet. The idea is to set up work to active-recovery ratios (work:active-recovery) in intervals of minutes.
For instance, let's say you usually train comfortably at 6 mph on the treadmill. So, after your warm up and a few minutes at 6 mph, you sprint for one minute at 7.5 mph and then jog again at 6 mph for three minutes (1:3 ratio: a total of four minutes). You continue these intervals for your entire workout and then cool down for about five minutes.
How do I determine how hard to work?
Heart rate is a good indicator of how hard you're working, and it's easy to measure, so it's an ideal method for setting up and monitoring intervals. Here's an example. Say your heart rate is 70% of your predicted maximum when you jog at 6 mph. After you warm up and spend a few minutes at that pace, you increase the speed for your work interval to 7 mph, which might be 85% or even 90% of heart rate max, and then you cut back on the speed to 6 mph at a heart rate of 70% of max for your active-recovery.
Below is a sample 28-minute interval workout (excluding warm-up and cooldown). Keep in mind that you can spend the entire workout doing them or vary it and do just some of the work intervals, and note that the time of each interval in this example always adds up to four minutes.
Sample HIIT Workout
- Warm-up: five minutes at 5-6 mph
- Interval 1: three minutes at 6 mph (70% of max heart rate)
- Interval 2: one minute at 7 mph (80% of max heart rate)
- Interval 3: three minutes at 6 mph
- Interval 4: one minute at 7 mph
- Interval 5: three minutes at 6 mph
- Interval 6 - harder: one minute at 7.5 mph (85% of max heart rate)
- Interval 7: three minutes at 6 mph
- Interval 8: one minute at 7.5 mph
- Interval 9: three minutes at 6 mph
- Interval 10: one minute 7.5 mph
- Interval 11: three minutes at 6 mph
- Interval 12: one minute 7.5 mph
- Interval 13: three minutes at 6 mph
- Interval 14: last push -- one minute at 8 mph (90% of heart rate max)
- Cool down: five minutes at 5-6 mph, then walk
Some athletes train as high as 100% of heart rate maximum. I don't recommend that beginners go above 85%-90%, and 1:3 work:active-recovery ratios are the standard starting point. Remember to stay well-hydrated during the entire exercise.
How often should I increase the intensity of the intervals?
Interval training will improve your conditioning and performance quickly, usually in just a few weeks. As your conditioning improves, your heart rate will be lower at both the work and active-recovery interval even though you are training at the same speed you started the intervals with. When that happens, you increase the work ratio by one-half minute or even a full minute and decrease the active-recovery interval.
For example, you change the 3:1 ratio to 2.5:1.5 or 2.0:2.0. You keep changing the ratio over the weeks until you are doing all the work intervals for four minutes and then you start over with a new 3:1 ratio.
Sample Six-Week Program
Here's an example of a six-week program using one-minute interval increases:
- Week one. 6 mph:7.5 mph (three minutes at 6 and one minute at 7.5)
- Week two. 6 mph:7.5 mph (2.0:2.0)
- Week three. 6 mph:7.5 mph (1:3)
- Week four. 6 mph:7.5 mph (all at 7.5 mph for four minutes) Now a new interval at higher speeds
- Week five. 6.5 mph:8 mph (3:1 minute)
- Week six. 6.5 mph:8 mph (2:2)
Important: Intervals are tough, and so you might want to increase each week in half-minute intervals. You should be out of breath and sweaty during the work interval to make it work but not so hard that you put yourself at risk for injury. For instance, if you can't run at 7.5 mph because your legs simply won't go that fast, then don't do it. Instead, you can increase the incline of the treadmill, and outdoors you can perform the work interval on a hill.
Listen to your body and experiment until you find what works best. It's much safer and more effective if you slowly and efficiently work up to a long-term goal rather than try to achieve it as quickly as possible.
How do I know how high my heart rate is?
The intensity of your intervals will make it tough to remain still enough to monitor your heart rate with your hands or even with the monitor on your treadmill or bike. This is where a heart-rate monitor comes in. They are excellent tools for measuring intensity during intervals. Heart-rate monitors can be easily found online — they can be inexpensive or you can opt for one with more features on the higher end.
Can I do intervals inside or outside, with or without exercise equipment?
Yes, intervals work both indoors and out. Your body won't know the difference between running sprints on a track or the treadmill, cycling on the road or on a stationary bike (spinning classes are great interval workouts), or working on an elliptical or any other exercise machine. You can do intervals with swimming, rowing, cross-country skiing, or any other sport you like. Intervals work as long as you get your heart rate pumping and follow the ratios.
How often should I do intervals?
Intervals are intense, and so I recommend only one or two sessions per week to start, with at least three days in between for recovery and growth. You can do more than one or two after six weeks of training. Overtraining is a common mistake of the overly eager beginner, and can lead to impaired health and performance.
Are there any disadvantages to interval training?
Intervals are tough on your body. If performed too often they increase the risk of overtraining. Overtraining is uncomfortable and a set back and so it's important to prevent it by allowing time for recover and growth between sessions. I recommend at least two days of rest between sessions and even more if you suspect you are becoming overtrained. Symptoms of overtraining are
- loss of strength speed, endurance, or other elements of performance,
- loss of appetite,
- inability to sleep well,
- chronic aches and pains or soreness,
- chronic colds or respiratory infections,
- overuse injuries like tendinitis,
- unusual fatigue,
- occasional increase in resting heart rate,
- irritability, and
- malaise and you don't feel like exercising anymore.
If you have any of these symptoms and it's from overtraining and not a medical condition (for which you should see your doctor), then you will need to either take a break from working out (generally seven to 10 days) or experiment with fewer intervals. Don't worry about losing your fitness if you take a break. Virtually everyone comes back stronger after a break.
NOTE 1: If you have trouble with your knees, then speeding up for work intervals of walking, jogging, or running, might be too tough. You don't want to irritate your joints, so stop the exercise that hurts and modify your workout to make it pain-free (or as close to pain-free as you can. You never want to work through pain, and especially pain that gets worse during your workout. See your doctor if pain persists.
NOTE 2: Check with your doctor before starting interval training if you have any questions about the health of your heart or other medical conditions that might be affected by high-intensity workouts.
What are the physiological effects of interval training, and how do they increase fitness and performance?
Imagine that your muscles are engines that burn fuel (fat and carbohydrate) to keep you going, and in that engine there are two energy systems, aerobic (more fat-burning) and anaerobic (more carbohydrate-burning). Athletes and others who play sports that demand stopping and starting, or individuals who participate in endurance events that include hills or a sprint at the end, require that the muscles switch quickly between both systems.
For example, say you're on a long-distance bike ride and you come to a large hill. Along the flat road your heart rate is at the low end of your training range and you're working aerobically and burning lots of fat (comparable to the active-recovery of your interval training session), but then you hit a very large hill. Now your heart rate increases and you start breathing harder (the work interval of your interval session), and so your muscles must make the switch to the anaerobic system where you burn more carbohydrate than fat.
If you've put your time in with interval workouts, then at the top of the hill you'll catch your breath quickly and be ready to go. But if you haven't been doing intervals, your recovery will be sluggish (your muscles don't make the switch back to aerobic metabolism) and your performance will be compromised. In a nutshell, interval training trains your muscles to switch quickly between the two energy systems to keep you going, and the results are awesome.
How do I know if I should do intervals?
There are several reasons why you might do intervals.
- Recovery is the best indication of fitness, and intervals dramatically improve recovery. Next time you climb a hill while running or biking, or climb a flight of stairs, or sprint down the field, check your recovery time. If you find yourself bent over catching your breath instead of getting right on with it, consider intervals. In just a few weeks, your recovery will improve.
- Intervals might help you break a weight-loss plateau. There are no studies that I am aware of to prove that intervals break weight-loss plateaus, but many individuals have reported this to me and I have seen it happen myself. I can't explain exactly why it works, nor does it work for everyone, but it's certainly worth the effort if your weight loss has stalled. At the very least, you will improve your fitness.
- Intervals might be just the thing if you're bored with your routine. First off, it's a new activity. Second, you experience results quickly (within a week or two), and nothing is more motivating and exciting than near-instant gratification!
Will interval training help me burn more calories and more fat?
Yes it will. Intervals improve your aerobic fitness level significantly, and when that happens, you're able to do more work and burn more calories (given the same amount of time and/or distance).
For instance, say you can only run on the treadmill at 6 mph. In 30 minutes at that speed, and if you weigh 150 pounds, you'll run 3 miles and burn 300 calories (100 calories per mile for a 150-pound person). However, if you're more fit and can run at 6.5 mph, then in 30 minutes, you'll run 3.25 miles and burn more calories. And as a bonus, you'll burn more fat as a result of your improved fitness.
Keep in mind that intervals are tough and could potentially increase your appetite. If that happens, I suggest that you drink lots of water when you do them, and that you have a snack with carbs and protein (and a little fat is OK) 20-30 minutes before you train. Energy bars or something like a bagel with peanut butter are good choices. Snacking before a workout usually decreases appetite afterward. You can also experiment with a small snack after your workout.
Will interval training help me lose weight?
The key to weight loss is to burn more calories than you consume. Intervals contribute to weight loss because they make you fitter, which allows you to work out harder and longer and burn more fat and more calories. But don't forget that you must burn more calories than you consume to lose weight even with intervals.
Is circuit training an interval-training workout?
Circuit training is where you spend 30-45 seconds at one weightlifting machine, or a station with dumbbells or a resistance exercise like crunches, and then move quickly to the next station. It's a great aerobic and resistance exercise workout in one, and yes, it is interval training because during the switch from one exercise station to another your heart rate will drop and then increase once you start working again at the next station. It won't work as well as dedicated running or cycling intervals to increase endurance and recovery, but it will tone and strengthen muscles, particularly in the upper body, and that's a benefit you don't typically get with intervals.
Is interval training the same as cross-training?
Interval training is not cross-training. Cross-training is a break from your normal workout where you train using alternative exercises. For instance, you could use the treadmill instead of the elliptical, the bike instead of the treadmill, or some other combination. With cross-training intervals, you could switch machines and start intervals (for example, switch from the elliptical to the treadmill), or you could stay on the elliptical and start intervals. A cross-training workout that includes intervals will increase your fitness and performance and can break up the boredom of your normal routine.
I'm a bodybuilder. Should I do intervals?
There's conflicting opinions on this. Some individuals suggest that intervals will burn too much muscle and reduce mass. Others argue that the conditioning from intervals will allow for more weight lifting in the gym, which ultimately leads to more muscle. I suggest experimenting until you find the right combination of intervals and weight lifting that works for you. Cut back on interval training if you find your muscle growth isn't what you expect or you're too tired from the intervals to give 100% to your bodybuilding workouts.
Should I warm up before interval training?
Absolutely. Intervals are tough on your muscles and your heart and so you need a good warm up beforehand. I recommend an 8-10 minute warm-up or performance at your active-recovery intensity before you hit the work intervals. It is always good to listen to your body. If you still don't feel warmend up and ready to begin intervals after the initial 10 minutes, then keep warming up for another five to seven minutes. A proper warm up is essential to injury prevention. As previously mentioned, consult with your doctor if you have any questions or concerns about interval training being too tough on your heart.
What should I do for a cool-down after interval work?
I recommend a minimum of five minutes of cool-down at a low intensity after your intervals. I also recommend stretching afterward because the leg muscles will be tight after an intense session. Quad, hamstring, calf, and low-back stretches will help. Sometimes muscles are too tight to stretch immediately after your interval session and so you might want to walk around for a bit and then stretch later in the day.
Wrapping it up
There you have it. Interval training is an efficient and effective training method that will help you improve your aerobic and anaerobic capacity, your performance, your recovery from short and intense bouts of work, and all in less than one-fifth the time of traditional aerobic conditioning. Intervals are tough but worth the effort. Give it a try and see what you think. Good luck with your training!
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Gibala MJ and others. "Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance." J Physiol. 575(Pt 3) Sept. 15, 2006:901-11.
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