Prescribing High Intensity Interval Training

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High-Intensity Interval Training or HIIT is a powerful tool for coaches, trainers, and trainees when prescribed correctly.


What Science Says

Even though the scope of this article is not to show all the research behind the prescription of HIIT, I’m going to name some of the benefits that science has proven:

  • Time-efficient. In a matter of minutes, you can get the same benefits of at least one hour of steady-state cardio or aerobic training.
  • It’s a superior way to lose fat compared to aerobic training.
  • It improves VO2Max and conditioning.
  • You can even gain muscle mass and strength.
  • Improves the metabolism leading to better insulin and blood sugar management.
  • Improves cardiovascular health.
  • Leads to better cortisol:testosterone ratio (anabolism instead of catabolism).

Parameters to Consider When Prescribing HIIT

Here are some of the parameters to consider:

  • Specific needs of the athlete/client.
  • How fast the athlete/client has to lose body fat or get higher conditioning levels.
  • How much time per week the athlete/client can perform HIIT.
  • The current level of conditioning of the athlete/client.
  • The current training program of the athlete/client at the gym.

Equipment to Perform HIIT

Of course, you can do your interval training without any equipment, but as some people might have the need to use it, this is my take on the matter.

As I mentioned in an old post, stay away from any type of equipment that is connected to the electricity. When you do your intervals on this type of electrical equipment, you are exposing yourself to dirty electricity which has proven to decrease insulin sensitivity, amongst others.

My Favorite Ways to Practice Interval Training are:

  • Sprinting upstairs: Provided that you have access to stairs, simply sprint upstairs for the prescribed time, and walk downstairs during the rest intervals
  • Sprinting uphill: go uphill as fast as you can and slowly go downhill during the rest period.
  • Sprints: even though I love sprinting, I don’t prescribe it much because the rate of injuries that I have seen is simply high. In order to perform real sprints, you need to properly warm up, and that is not a matter of a few minutes. It takes time and dedication. I only prescribe sprints to athletes that have mastered the correct sprinting technique and are aware of the importance of a proper warm-up.
  • Spinning bicycle: in this case, you better go for strength and not for high Revolutions per Minute (RPM) on the pedals. Pedaling hard, strength-wise is what brings the higher adaptation levels. If you have one of those gadgets that can measure power on a spin bike, measure your watts.
  • Concept II Rows: Same as in the bicycle, choose resistance instead of speed, and on this piece of equipment, always measure watts.
  • Woodway unmotorized treadmill: even though is not the best option, it’s a feasible alternative to perform interval training. For this ergometer, choose speed as the variable to be measured.

How do I Prescribe HIIT?

There is a common factor in the design and prescription of the intervals training. It’s not a matter of just going outside or to the gym and doing any length of work interval and any length of the rest period. It must have a structure and that structure should match with the current training program the athlete/client is performing at the moment.

The principle that regulates this concept is the principle of consistency. It wouldn’t make much sense if you are training somebody in the gym to become faster and prescribe interval training that will provide endurance.

And this brings me to the energy systems, which are basically related to the form of energy that your body will use and the waste product that it will produce when engaging in physical activity. There are 3 major energy systems:

  • Anaerobic Alactic: does not require the use of oxygen and does not produce lactic acid.
  • Anaerobic Lactic: does not require the use of oxygen and produces lactic acid.
  • Aerobic: requires the use of oxygen.

And each of these subdivides in 2:

  • Power: can be understood as the size of the engine.
  • Capacity: can be understood as the size of the fuel tank.

Getting into the exact details of this matter is out of the scope of this article, and it is a subject I fully address in the online class Science of Program Design.

Going back to the principle of consistency, if the training program is in the range of a time under tension of 50-60 seconds, that should be the length of the working part of the intervals. And as an extension, the same principle applies to the rest intervals, meaning that the rest intervals for the same muscle group on the training program, should be the same rest period on the interval training.

Here is an example:

Let’s say your training program is as follows:

A1. Chin-Ups to Sternum Mid Supinated Grip, 8 x 8, 4-0-1-0, rest 90 seconds

A2. Dips for Chest on V-Bars, 8 x 8, 4-0-1-0, rest 90 seconds

This means that the time under tension for both exercises is 40 seconds (8 reps x 5 seconds), and the rest period between agonists (Chin-Ups) is 180 seconds (90 + 90 seconds).

In this sense, the prescription for the interval training should be done in 40 seconds of work 180 seconds of rest.

Of course, there is some space in the prescription, especially if you want to work the power or capacity component of the energy system, or if you want to slightly decrease (10-15 seconds) the rest interval every 2 sessions in order to force adaptation in terms of conditioning and fat loss.

Going back to the concept of consistency, the whole point is to stay within the same energy system that the client/athlete is using in the gym.

How many sets for the interval training?

This question takes me to the principle of the critical drop-off point. This means that when the magnitude of the power decreases significantly, it’s time to stop the exercise.

Using the rowing ergometer as an example, let’s say you can maintain a power output of about 400 watts during the 40 seconds of work on the intervals. If that power goes below 350 watts in any given interval, it’s time to stop the training session. As you can see, it’s a day-by-day matter.

When sprinting you can do it by measuring distance. When you fall short on covering the distance for about 10%, it’s time to stop.

How hard should I go and how should I rest?

Continuing with the example above, the work part of the intervals should be maximal exertion! That means that if you try to sprint for 41 seconds, you will fall face to the ground. The same applies to bicycles and the other ergometers/forms.

About the rest period, if you are sprinting just walk, if you are pedaling, simply totally reduce the resistance and keep pedaling slowly, if you are rowing, just walk around the machine.

Frequency of interval training

Basically, the goal or needs of the athlete/client will determine the frequency of training. A few cases:

If an athlete/client requires to dramatically improve the conditioning in a short period of time, I normally program the weight training session in the morning and the interval training 4-6 hours after. This is normally done 4-5 times a week. The same principle applies to someone who rapidly needs to lose body fat.

If the athlete/client is relatively lean and conditioned and needs to improve the conditioning a bit more and lean out, I plan the intervals on the rest days from weight training. Let’s say this athlete/client trains 4 times per week (Monday, Tuesday, Thursday, Friday), is 12% body fat, and is running out of breath by the end of certain training programs or by the end of the sports practice, I plan the interval training on Wednesdays and Saturdays. It’s very important to keep in mind that the athlete/client MUST have a FULL day of rest during the week.

For general health and maintenance, I prescribe interval training once per week, on one of the days off from lifting weights.


If your athlete/client is going to embark on HIIT, I strongly recommend rotating the ergometers in order to prevent adaptation.

If you plan it and prescribe it properly, HIIT is powerful and will accelerate the results on your athletes/clients and yourself.

Coach Carlos Castro

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