One of the most exciting areas of physiological improvement seen in people following a High Intensity Interval Training programme has been an increase in mitochondrial density (or, in simple terms, the number of mitochondria).

If you think back to my article on base training, you will remember that mitochondria are the power stations of our cells. This is where the energy needed to produce power on the bike is produced and so the higher your mitochondrial density, the more power you will be able to sustain. Sounds great, right?

Traditionally it has been thought that the way to improve mitochondrial density was to follow a training plan of continuous aerobic exercise – also known as base training. However, in 2008 an exercise physiologist called Karl Burgomaster carried out research that showed a HIIT programme gave similar benefits in the quantity of oxidative enzymes (the substance in the mitochondria that processes oxygen) compared with traditional base training. He showed that a series of 4-5 x 30-second sprints with 4-5mins recovery, just three days a week, was the equivalent to 40-60mins of base training five times a week.

Needless to say, this is obviously a time efficient way of bringing around the same sort of fitness benefits associated with a more laborious training programme – but HIIT has limitations of its own.