High-Intensity Interval Training (HIIT)

Cardiovascular training varies in its degree of impact, level of intensity, and duration of exercise. You should pay close attention to these factors before you select a fitness routine. The current condition of your body will help determine the proper type of cardio training for you.

Basically, there are two main types of cardiovascular training you need to know about:

• Low-intensity steady state cardio (slow prolonged duration cardio training) or “LISS”
• High-intensity interval training (HIIT)

What is high-intensity interval training (HIIT)?

Steady pace training – keeping your heart rate fairly constant throughout your workout – builds endurance and a good base level of fitness. Interval training – exercising for short periods at a high intensity, interspersed with lower-intensity recovery periods – builds cardiovascular strength and stamina. The heart and lungs are worked harder during this type of training so they will become stronger and, as a result, you become fitter.

Basically, HIIT is equivalent to a 30-60 second sprint (defined as “work”), followed by a 15-30-second walk/jogging (defined as “rest”). These “work” and “rest” periods are then repeated for a designated amount of time, usually 10-20 minutes.

This simply means to vary intensity of cardio activity. For example, increase the resistance level on a stationary bike or increase your speed while running on the treadmill. The duration of those high intensity intervals is variable and completely up to you. However, to improve your fitness level, your work time must exceed your recovery time. For example, if you run (sprint) one minute you will have to jog for less than that (e.g., 30 seconds).

During interval training, you tax your heart and then let it recover while you continue to work at a less intense level. In other words, you raise your work level and then from that state occasionally go higher to an anaerobic state (workout without oxygen, almost breathless). You then return to the original level which is not rest, but the previous aerobic state. This state is called active recovery, and the exercise intensity is low enough to facilitate the removal of lactate, a by-product of one of the systems that creates energy for your body.

Target heart-rate zone for high-intensity interval training

Also note that the shorter the interval is, the harder you should be pushing yourself as you move through it. If you’re just doing very short fifteen second intervals, you really want to be pushing your body to the limit. On the contrary, if you’re using longer intervals, you can bring down the pace slightly so that you can sustain the interval for the intended period of time.

Training duration

An HIIT session can last anywhere from 10-20 minutes. Since the intensity is very high and the effort is usually an all out effort, 20 minutes is the maximum duration required. This is enough time for you to complete six to twelve intervals (depending on the interval and rest period lengths).

What is “negative” rest?

The protocol for this type of cardio is to perform “negative” rest. Negative rest simply means you would rest for a lower period than you worked. For example, Jim is doing HIIT on the treadmill for 15 minutes. He is sprinting for 45 seconds and resting for 15 seconds. His rest consists of decreasing the speed and briskly walking for 15 seconds to recover before he has to sprint again.

Who can specially benefit from this type of cardiovascular training?

If you are an avid exerciser, steady state training will maintain your fitness level and you will eventually reach a cardiovascular plateau. To improve your fitness level, think about incorporating some interval training into your program to change your routine and make your body work harder via active recovery.

Advantages of high-intensity interval training

The great advantage to interval training is that more work is done in the same amount of time as in a traditional class (low-intensity steady state cardio), offering such benefits as more caloric expenditure, more cardiovascular training, and more VO2 max training. VO2 max training refers to the capacity of the lungs to use air; the more fit you are, the higher your VO2 max is.

Secondly, one of the biggest benefits of HIIT training is something called “EPOC” (excess post-exercise oxygen consumption). The story behind this fancy term is very simple. High-intensity bouts keep your metabolism elevated at a higher rate and for a longer period after the exercise is over. This means while you’re relaxing in your family room watching TV after completing your HIIT training session you will continue to reap the benefits of your workout because your body will continue to burn oxygen, calories, and fat at a higher rate for many hours.

Finally, interval cardio training is also going to work on your speed and power development as well, as you’ll rapidly have to accelerate quickly when doing each interval.

Drawbacks of high-intensity interval training

Its main drawback is that while some of the energy comes from fat, most of it is derived from reserves of carbohydrate (glycogen inside the muscle). This is an inefficient way of losing fat. The best way is to burn fat rather than carbohydrate.

Exactly which energy source is preferred during physical activity is based upon the level of intensity that’s required. Exercising with a relatively high level of intensity uses a greater percentage of carbohydrates as an energy source; exercising with relatively low level of intensity uses a greater percentage of fat as an energy source.

When to make the endurance method (LISS) your first choice?

Making use of the interval method is not an easy task. Going to the limit during intense interval trainings makes you feel as if your heart is going to burst. This can be painful and you will probably run out of breath fast. However, if your motivation to burn as much body fat as possible is strong enough, you will withstand the discomfort of intense cardio activity knowing that you are going to achieve excellent results. However, in case of low carbohydrate dieting, you may feel a depletion of energy on some days. Those are the days to make the endurance method your first choice when doing aerobic exercise. For example, riding a bike at a constant, moderate intensity level or a low speed, or running at a steady speed without any increases.

Low-intensity steady state cardio (LISS) Versus HIIT

While it’s probably true that exercising at the lower zone will burn more calories in the form of fat, exercising in the higher zone will certainly burn more calories overall for the same amount of time. And since total calorie expenditure is the key to losing fat, theoretically the higher zone should be the best zone. Furthermore, after a HIIT workout, you continue to burn more calories throughout the day as your body works to restore your preworkout oxygen levels.

The key word there is “should” as everyone’s body responds differently. The lower zone may work best for you. Our advice is to start out at the lower zone and gradually work into the upper zone and see what happens. If there is a noticeable difference then select the one that works best. If on the other hand both seem to be yielding equal results, then alternate them. You can alternate them on a daily basis (i.e. high, low. high, low, etc), or one month high and the next low.

The truth is that both high-intensity interval training and steady-state cardio are effective in their own ways. The best system of cardiovascular training probably isn’t the all-or-nothing approach. Rather, it’s a blend of both higher and lower-intensity cardiovascular training that’s tailored to your body and your goals.

Closing thoughts

High-intensity interval training differs from steady state training. The latter refers to any cardiovascular activity aimed at maintaining your heart rate at a consistent level. If you are not in the condition or you are new to fitness, steady state training will improve your fitness level. However, if you are an avid exerciser, steady state training will maintain your fitness level. That means you will eventually reach a cardiovascular plateau.

To improve your fitness level, think about incorporating some interval training into your program to change your routine and make your body work harder via active recovery. During the interval phases, you increase either your speed or the resistance of the machine. HIIT’s major advantage is that it burns maximal calories in a short period of time. Furthermore, high-intensity bouts keep your metabolism elevated at a higher rate and for a longer period after the exercise is over. That is why a solid fitness routine includes HIIT and steady-state components.