Why Train at High Intensities?

dan powell smart performance torbay sport south devon science guy

Why Train at High Intensities?

It has long been believed that the best way to reduce body fat is through the use of long slow duration training (typical endurance training) i.e. running on a treadmill/road for time periods of around 30-60 minutes or longer in what is labelled the ‘FAT BURNING ZONE’.

Although there is no escaping that endurance training at low intensities (60-80% VO² max) provides a major stimulus for the body to adapt to use fatty acid oxidation to fuel exercise and increase energy expenditure, this training modality imposes a lesser amount of post-exercise stimulus. Therefore, the question should be: is this method the most effective way to reduce body fat for the everyday person who has an extremely busy lifestyle?
On the contrary, high intensity training (HIT) has been shown to be extremely effective in reducing body fat, up to nine times greater than endurance training over the same period of time (Tremblay, 1994). Although this HIT training mainly uses carbohydrates to fuel exercise, what occurs during recovery after HIT is very different to endurance exercise. Excess Post-exercise Oxygen Consumption (EPOC) has a major influence on the amount of fatty acid oxidation during recovery from exercise: the longer and more intense the exercise the greater the EPOC.

When we start to exercise the body goes into oxygen debt; this is when the demand for oxygen is greater than what our body can supply; the greater the duration and intensity, the greater the debt. Therefore, during recovery the body needs to restore itself to the pre-exercise condition (Lee, Ha & Lee, 1999; McArdle, Katch & Katch, 2007).

Ways in which EPOC increase fatty acid oxidation during recovery (McArdle, Katch & Katch, 2007):

  1. Restoring energy stores.
  2. Changing lactate acid back to glycogen.
  3. Oxidising lactate in energy metabolism.
  4. Restoring oxygen to myoglobin in the blood.
  5. Thermogenic effects of elevated core temperature.
  6. Thermogenic effects of hormones.
  7. Effects of elevated heart rate, ventilation and other physiological functions.


In addition to the increases in fatty acid oxidation seen during recovery, HIT has also been shown to have other benefits when compared to traditional endurance training. Not only has it been shown to improve time trial performance to the same degree as endurance training but these improved performance times were seen with a 90% reduction in training volume (Gibala et al, 2006) indicating a time effective method to improve fitness levels.

In summary, the research indicates that, because of the elevated processes the body goes through to recover from HIT, it is an extremely effective method to improve body composition through reduction in body fat. Moreover, HIT also seems to be a time efficient method to improve fitness levels, therefore improving endurance performance. This, however, doesn’t mean you shouldn’t be doing your long slow runs, if training for a marathon for instance. That method of training still holds value in the whole training programme.

Dan Powell MSc, BSc (Hons) ASCC

Gibala, M. J., Little, J. P., van Essen, M., Wilkin, G. P., Burgomaster, K. A., Safdar, A., Raha, S and Tarnopolsky, M. A. (2006). Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. Journal of Physiology. 575. pp. 901-911.
Lee, Y. S., Ha, M.S and Lee, Y. J. (1999). The effects of various intensities and durations of exercise with and without glucose in milk ingestion on post-exercise oxygen consumption. Journal of Sports Medicine and Physical Fitness. 39 (4). pp 341-347.
McArdle, W.D, Katch, F.I and Katch, V.L. (2007). Exercise physiology, energy, nutrition and human performance. Baltimore, Maryland. Lippincott, Williams and Wilkins.
Tremblay, A., Simoneau, J. A and Bouchard, C. (1994). Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism. 43 (7). pp 814-818.

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