The “411” on High Intensity Interval Training (HIIT) in 2001

What Is HIIT?

High-intensity interval training (HIIT) is often described as “doing intervals” but this is inexact. More precisely, the idea with HIIT is to alternate periods of brief, high intensity (i.e., anaerobic or maximal exertion) exercise with equal, shorter, or longer duration periods (or distances) in lower exertion zones. Alternating between warm-up and aerobic levels would qualify as intervals but not as HIIT. So, while all HIIT are intervals, not all intervals count as HIIT.

HIIT is neither about sustained anaerobic nor sustained aerobic effort; it is about alternating periods within the same workout session. Neglecting the lower intensity segments for recovery and recuperation will obstruct reaching maximum or near maximum intensity – 95 % or more of maximum heart rate – repeatedly.

How It Works

While HIIT makes forays out of the fat burning zone, it actually prompts so-called excess post-exercise oxygen consumption (EPOC). This means the body will expend energy recovering from the high-intensity workout after the workout has finished.

When training purely for endurance or purely for musculoskeletal strength and power, the most appropriate muscle fiber type develops toward its ideal condition and less appropriate types adapt as well as they can. HIIT, however, more evenly stimulates all the muscle fiber types in the body, from endurance-leaning slow twitch to power-leaning fast twitch.

Benefits and Drawbacks

HIIT, in less time, stimulates many of the same bodily responses of endurance training as well as speed training. HIIT is generally beneficial in the triad of physical fitness and athleticism, offering improvements in:

  1. Cardiovascular and respiratory endurance represented by the ability to capture and deliver large quantities of oxygenated blood (and remove metabolic wastes) throughout the body over extended periods;
  2. Musculoskeletal strength represented by bone density, muscle mass, and power; and
  3. Neuromuscular linkage represented by coordination, quickness, and agility.

HIIT will encourage fat loss and a faster metabolism too and is excellent for increasing one’s VO2 max.

Continuous, regular exercise in the aerobic zone improves cardiovascular and respiratory endurance. However, long sessions – like 30 minutes or more – of sustained, moderate-intensity exercise will encourage catabolism of excess muscle mass (imagine a bodybuilder converting into a marathon runner). On the other hand, HIIT supported by a dietary caloric surplus originating in proteins can be anabolic (imagine a marathon runner converting into a sprinter). HIIT, considering body type with a proper diet, should support modest muscle gains while reducing body fat!

What are the drawbacks of HIIT? These intervals are not ideal for all athletes pursuing specific goals and results. Exclusive HIIT will not suffice if an athlete – like an ultra-marathon runner – is looking to develop peak endurance; sustained (i.e., steady-state) distance training in the aerobic zone would be the cornerstone of such a pursuit. As well, improperly structured or excessive HIIT could be a hindrance for athletes desiring massive muscle gains in short order.

Putting High Intensity Intervals into Your Training

Intervals of higher intensity can be introduced while running, jumping rope, stair climbing, and in other activities. Track-and-field athletes will be familiar with “alternating blocks,” whereby one city block will be covered at a full sprint and the next at a jog. Athletes in many other sports run “wind sprints” with the same aim.

Beginners should try to do 10 to 15 minutes of intervals. Begin with a steady-state warm up lasting 2 to 5 minutes. When you’re warm up period is over, bump up your intensity into the fat burning zone (if you can handle it go into the aerobic zone) for 1 to 2 minutes. Either way, this would mean a non-leisurely pace and a level of exertion that breaks a sweat. When the minute or two is up, now you should do your first high-intensity interval for 15 to 30 seconds. This means your maximum effort with your lungs and muscles burning! Alternate from 1 to 2 minute recovery intervals in the fat burning/aerobic zone to 15 to 30 seconds of your best effort; finish with a steady-state cool down of 2 minutes.

Intermediate-level trainees should try making things more challenging. The challenge can come from extending your HIIT session to 15 or 20 minutes, moving from the fat burning zone to the aerobic zone, reducing recovery periods from 2 minutes to 1 minute, or raising high-intensity intervals up to and over 30 seconds.

Advanced athletes should make things harder still. Here, your recovery periods should never drop below the aerobic level. Your sessions may actually fall below 10 minutes but your recovery periods would be under 1 minute. High-intensity intervals will extend to 1 minute or more to simulate an actual dash – like 400 meters – on the track or a round in the ring.

HIIT may take 24 hours or more to fully recuperate and may preclude your best effort in other types of training the following day.

Is HIIT Right for You?

High-intensity interval training (HIIT) is not for everyone. It demands an unambiguous departure from levels of effort considered comfortable and not everyone is mentally or physically up to the challenge. If there are risk factors for an individual, a stress test might be appropriate.

For the most part, HIIT yields much the same benefits as conventional endurance training with benefits not offered by conventional endurance training. If your interest is in a sport-specific training practice, general fitness, or in burning fat while engaging in a shorter workout, HIIT is worthwhile. For some athletes, HIIT should be considered essential.

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