Bursts of cardio

Is it true that doing short, intense bursts of cardio (intervals) is more effective for weight loss? If so, how long should I do this for, how long should these bursts of speed last and how long should the rest/less intense periods last?

TOM SAYS:

Yes it is true. Click here to read more about high intensity interval training

I do a little bit after most of my workouts - approximately 5-10 minutes of it. It's really tough and it's a much more fun way of training than boring old cardio...seriously, once you've tried this training you'll never go back. Cardio is SO BORING in comparison.

I usually do a 1:1 ratio of sprint to slow-pace. And I don't necessarily keep the interval lengths constant.

I might go...

• 30s Sprint 30s Slow


• 15s Sprint 15s Slow


• 30s Sprint 30s Slow


• 10s Sprint 10s Slow

...just whatever I feel like. It makes it more fun when you can change it up a lot. If you don't feel like you could possibly face another 30s all out sprint, you can break it down into 3 smaller 10s sprints.

Interval training is not something you should do too often though. It is quite stressful on your body (which is good for getting fitter) so you'll need rest periods. Take a week off every now and again, or at least reduce the intensity of your training.

It's also not something you should do if you are a beginner. You need to have at least some base level of fitness first. Otherwise it can lead to injuries and burnout.

Hope that helps
Tom :)

UPDATE - 20th May 2010

Since I answered this question first, I have done some more research.

Apparently it is better to do longer intervals of approximately 60s to 90s.

If you are interested why...here's a slightly simplified explanation.

When you sprint you're using your body's anaerobic energy system.

There are 2 metabolic pathways by which anaerobic energy is generated. The first is the phosphagen system which can generate energy for approximately 30s. The second is the glycolytic system which can generate energy for around 60s to 2 mins.

The reason why increasing the intervals to over 60s is because we want to make full use of the glycolytic system.

This pathway drains muscle glycogen which is important for 2 reasons.

1. Muscles low on glycogen will suck up glycogen from your bloodstream - which previously would have been stored as fat if unused.

2. Circulating fatty acids are increasingly used for fuel instead of glycogen.

Basically you're storing less sugar as fat and the fat you already have is preferentially for fuel.

That's perfect for weight loss.
Enjoy!

P.S. You'll have to decrease your intensity if you want to got for 90s. Aim for about 75% of your maximum speed.