High Intensity Workouts: Fitness in Less Time

Chapter summary

Good vascular function is critical for health. Endurance training (ET), three to five hours a week of running or gym work, is the standard way to build it.
High intensity training (HIT) and sprint interval training (SIT) are as effective as ET for most medical benefits.
Both reduce arterial stiffness, increase muscle capillary growth and raise eNOS (an enzyme that helps blood vessels relax).
Both improve small and large blood vessel function in muscle. SIT is the most time-efficient.

Anton Wagenmakers (Liverpool John Moores University) found the same results in under a third of the time. This was shown in the BBC Horizon documentary “The Truth About Exercise” with Dr Michael Mosley.
WHO and most health departments recommend three to five hours of endurance training a week. Most people cannot set aside that much time.
HIT: 15 to 60-second bursts of high intensity cycling, with two to four minutes of easy cycling in between. It can be done on an ordinary spinning bike and suits any individual.
SIT: four to six repeated all-out sprints of about 30 seconds with recovery in between.
Mechanisms: better delivery of insulin and glucose to muscle, more burning of fat stored in muscle fibres, and less stiffness in large arteries.
The results are not one-off. Cocks and colleagues (2013) compared SIT and ET and found similar gains in vascular health.
University of Birmingham pilot: sedentary adults aged 25 to 60 found HIT on spinning bikes more enjoyable than endurance training.

Supporters: A few minutes of intense effort a week delivers the benefit. This beats the time barrier.
The author’s doubt: He does not see it changing the 70% of people who do not exercise. He has tried SIT and says it is not easy, and that to be effective you have to push to your limit. “I can’t be bothered” remains the issue, so it is about change management and motivation.
Caution: These are small studies. Anyone with heart disease or who has been sedentary should see a doctor before starting hard exercise.
Weight: As the previous chapter says, exercise is for health, not for weight loss.

If time is your barrier, intervals can give a lot of benefit for minutes of effort.
Pair it with slow movement and less sitting.
Start after the first diet changes, not at the same time.

Cocks, M. et al. (2013) Sprint interval and endurance training are equally effective in increasing muscle microvascular density and eNOS content in sedentary males. J Physiol 591:641-656.
Mosley, M. (2012) The Truth About Exercise. BBC Horizon.
ScienceDaily (2013) Getting fit fast: inactive people can achieve major health and fitness gains in a fraction of the time.
Australian Bureau of Statistics (2006) Participation in Sports and Physical Recreation, Australia, 2005-06 (cat. 4177.0).