Interval Training is a fun and effective way to improve fitness, health and performance, but how much interval training is too much?


The Cost of HIIT

In an earlier article, I talked about the costs of performing too much High-Intensity Interval Training. These costs eventually surface as nagging injuries, zombie-like fatigue or reduced performance. These effects are brought about by cells in the body becoming too acidic.

Now don’t get me wrong, I am not anti-Interval Training, far from it – most of my swimming and indoor rowing achievements have been built on a heavy dose of interval work. However current research and anecdotal experiences have proved that you can get too much of a good thing (well, unless it’s peanut butter!).

When I talk about the ‘damaging’ results of interval training, I am talking about daily maximal effort intervals between 30 seconds and 2 minutes, with short rest periods. These intervals are focussed on the glycolytic energy system – the by-product of this is burning muscles and the desire to puke. In this article I want to introduce a method of interval training that will still allow you to build fitness and performance, but without those damaging side effects.


Energy Systems

The human body runs using 3 energy systems. These systems are always working together, but each system is dominant within the following time domains:

  1. Creatine Phosphate (CP) – 10 to 15 seconds
  2. Glycolytic – 30 seconds to 2 minutes
  3. Oxidative/Aerobic > 2 minutes

The CP system runs out quickly but it is incredibly powerful. Think of it like the drag car – it can’t be beaten but the maximum power runs out quickly.

The Glycolytic system kicks in after the CP system, and the power is turned down slightly. It will dominate up to 2 minutes. This is the boy racer – pretty quick, but produces lots of smoke (lactic acid) and then the exhaust pipe falls off.

The Aerobic system is in its element after 2 minutes. It is the least powerful of the three but it is the eco-car – it can run and run at low speed without any harmful side effects.

If you are an athlete then your training will likely be programmed such that you are performing in the appropriate energy system at the right time.

However, for the recreational gym nut, they tend to spend far too much time beasting themselves in the boy racer zone, and in doing so neglect their complete cardiovascular development. It is critical to remember that all three energy systems are important.

Anti-Glycolytic Training

Russian sports scientist Yuri Verkhoshansky (the pioneer of plyometrics) has researched the benefits of anti-glycolytic training. This is training that seeks to squeeze the glycolytic energy system by making the CP and aerobic engines bigger – we are trying to make the drag car last longer by using eco-technology. So rather than trying to make our bodies more tolerant to the effects of glycolytic training (the burning sensation), we are trying to keep the burning sensation at bay.

If a maximal effort sprint lasts for about 15 seconds, then how do we recover? The answer is by using the aerobic system! The aerobic system uses oxygen to regenerate ATP (the energy currency) so that the CP system is ready to go full throttle again. So If you have a poor aerobic function then you will need much longer to recover between sprints.


A number of studies have been conducted on ball sports – rugby, football, hurling. These studies show that approximately 70 – 80% of the game, players are using the aerobic system (jogging, running backwards, lateral movement), and 5% of the time they were using the CP system (sprinting, scrummaging, tackling).

The rest of the duration was made up of stoppages and standing around. Although the glycolytic system was used its contribution was much smaller than expected. So next time you watch a game, keep your eyes on a player for a few minutes (not the ball) and you’ll see this in effect – sprint, jog, sprint, jog etc  – as they switch between CP and aerobic energy systems.

How to Use It

One of the easiest ways to programme anti-glycolytic intervals into your programme is to perform flat-out sprints between 6 and 15 seconds. The CP system typically requires a work to rest ratio of 1:6-12. This means for 10 seconds work you are looking at 60 seconds to 120 seconds rest. The recovery should be something like easy walking whilst shaking the hands and legs off. It is during the walking that the aerobic system is working hard – you are likely panting, but your heart rate is dropping and your body is recharging the CP system.

You can play around with the work to rest ratio. The fitter you are, the more likely you can work on the reduced rest period. The key is to avoid the burn and to repeat the sprint once you are comfortably able to breathe through your nose once more.

“But I don’t need that much rest” – that’s because you aren’t working at the right intensity. The idea is to produce a maximal intensity effort, to rest, and then to repeat that maximal intensity effort at the same quality. If you are only taking 20 seconds to rest then either you aren’t being explosive enough on the sprint or the quality of each subsequent interval will be dropping (back in the boy racer zone).

You might start by performing 10 minutes of total work, but as you get fitter and your energy systems adapt then you can push this all the way up to 40 minutes.

Imagine how fit you will be when you can perform high-quality sprints for that length of time!

What to use

The best exercises to use with this are those that stimulate the whole body with maximal power. Good examples include…

  • Sprinting.
  • Prowler pushing at approx. 30 – 50% max load.
  • Hill sprints.
  • Rowing.
  • Kettlebell swings – using a kettlebell close to 30% of bodyweight.
  • Assault bike.

Example Sessions

Session 1 – Sprint 8 seconds max effort – rest 60 seconds* (repeat 10 times).
Session 2 – Prowler (load 30 to 50% max) 10 metres max effort – every minute on the minute* (repeat 15 times).
Session 3 – Assault Bike 15 seconds max effort – rest 90 seconds* (repeat 10 times).

* Lengthen the rest period if the quality of your sprints is decreasing.

Remember that this is an alternative to traditional HIIT. However, it is important to develop all energy systems in your conditioning. This might include low-intensity steady-state (LISS) work, anti-glycolytic training AND High-Intensity Interval Training.

Be bulletproof.

Coach Craig.

Author - Craig Peterson - Personal Trainer & Mentor

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