Interval training: How it works

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What is it?

A lot of race training plans suggest that you do intervals – also known as speedwork. The session is designed to get you used to running at speed and, used well, it can do wonders for your fitness – although it’s not exactly a walk in the park. When you started running, you probably went through a period of mixing up running and walking. Interval training is based on the same principle. In simple terms, you run fast for a bit, then you take an ‘interval’ to recover and get your breath back (this is where the session gets its name from), and then you do it again for a number of ‘repeats’.

Sounds hard. What are the benefits?

When you reach the point where you’re running a decent mileage but your performance has reached a plateau, it’s time to consider incorporating an interval training session into your weekly schedule.

Hardworking muscles produce lactic acid. If you’re running at a comfortable pace, your body has the ability to flush it away. But as you start to run faster and work harder, there comes a point when your body can’t do that quickly enough. The lactic acid builds up, leaving you with burning muscles – and a burning desire to stop. Interval workouts push you just above this point so your body learns to process the lactic acid faster and your muscles become more efficient, and the recovery intervals give you the chance to do this repeatedly.

I’m a beginner. Should I do them straight away?

It’s wise not to rush into it, especially if you’re a novice. Bones, tendons, muscles and brains need time to adapt to the stresses of regular training. The great news is that you don’t need to do intervals from day one. If you’re running less than about 20 miles a week, a gradual and consistent increase in your mileage should be enough to improve your times without speedwork.

How often?

A weekly interval session (with a week off every now and then) will do wonders for your race times.

How fast should I run each repeat?

Typically, your 5K pace is a good starting point, but you can also aim for 85 per cent of your maximum heartrate, or an eight or nine out of 10 on a scale of how hard you’re pushing yourself. Aim to run your final interval at the same pace (or in the same time) as your first one – setting off like a scalded cat is counterproductive as it means you take longer to recover, and can compromise not just the rest of the session but your next one too. It can take practice to get it right, but finishing strongly is great for your confidence.

And the recoveries?

Adequate rest between efforts is important. Even though you’ve taken your foot off the gas, your body is still trying to bring things under control, and it’s all part of the adaptation process. Once again, it can take a bit of adjustment to get the length right, but you should at least feel capable of jogging by the time the recovery ends.

Does the workout vary much?

There are three variables – the length of repeat, the number of repeats and duration of the recovery intervals. So naturally, the sessions are easily tweakable, and the choice of session can depend on your goal race distance and your fitness level. Take time to learn what works for you – at first, it’s better to undercook your pace and overcook your recoveries. As you progress, your pace will improve, your recoveries will be more effective and you’ll be able to run for longer. 

SIMPLE SAMPLE SESSIONS

The following sessions are popular:

  • 8x400m with 1-min recoveries
  • 5x800m with 2-min recoveries
  • 3x1 mile with 3-min recoveries 

But you can also get inventive. Mix things up with a pyramid session: 400m, 800m, 1200m, 1600m, 1200m, 800m, 400m, with varying recoveries. It’s a tough workout, so start with a 1:1 repeat-to-recovery ratio, and gradually cut the recovery time as you get fitter.