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What’s the best interval session?

Michael Donlevy
11 Mar 2020

They’re key to cycling fitness, but how do you decide which interval timing will work best?

It’s well known that interval training – where you break up a session with high-intensity bursts followed by periods of recovery – is a great way to build fitness for a summer full of cycling.

The beauty is that the variations are virtually limitless, but that can also make it hard to know what works best. So is one type of interval better than another?

‘Yes and no,’ says British Cycling coach Will Newton, helpfully. But he has a point. ‘What you do has to be specific to you as an athlete.

‘So if you’re a long-distance time-triallist you need to do long intervals at the pace you race at. Those intervals won’t work if you’re doing a one-hour circuit race.’

Paul Butler, founder of PB Cycle Coaching, agrees, but adds, ‘If one of my clients is aiming to complete a 100-mile ride but only has an hour at a time to train, I would often prescribe intervals to make the most efficient use of their time.’

‘There are so many ways to do them,’ says coach Ric Stern of RST Sport. ‘Intervals target different areas of physiology – one could work on anaerobic capacity, another the aerobic system. However, within each target area there’s more than one way to approach a specific goal. 

‘So to increase functional threshold power [FTP, your ability to sustain the highest possible power output over 60 minutes] you could use the popular 2x20 minutes at just below FTP.

‘But some people may not be up for smacking themselves stupid with such a long, arduous approach, so could use a session of 8x5 minutes at a marginally higher power output, maybe even of only 5 watts. 

‘There are pros and cons for all sessions,’ he adds. ‘The 2x20 interval allows you to work on long, constant efforts and build endurance, whereas shorter intervals will require a higher power output and will force slightly different adaptations.’

For an explanation of what FTP is, see here.

A key word loved by coaches is specicifity. ‘The closer you are to your event, the more specific your training should be,’ says Butler.

‘If you’re training for a flat crit race, find a flat road and do lots of sprints and max-effort intervals of 10 seconds to one minute to simulate the repeated attacks and accelerations out of the corners.

‘But if you’re preparing for a 10-mile time-trial, perform some eight-minute intervals at an intensity above that of your last race.’

Stern agrees, adding, ‘If you’re going to be doing lots of climbing in a race, it makes sense to do lots of training and intervals uphill because adaptations within your cells are specific to the joint angle and velocity at which they’re trained – and this will be different uphill to on the flat.’

If you’re really not sure what you should be doing, coach Stern has some advice: ‘Hire a coach! It’s a tricky balance because not only do the duration and intensity of the intervals have an effect on what you’re trying to achieve, so does the recovery period.

‘There’s no set formula, and a lot of it can be a judgement call by a coach.’

Fluid thinking

What if you’re not in training for a race? ‘If general fitness is the goal, start with a manageable level and then each session make one change to increase the difficulty,’ says Butler.

‘You could increase the number of intervals, the interval length or the intensity, decrease the recovery time or increase the frequency of the workout. Whatever you do, make the increments gradual to prevent injury or burn-out.’

Don’t just jump straight in, though. ‘Beginners need a basic level of fitness,’ says Butler. ‘For everyone else the risk is overtraining because intervals are very catabolic – they break the body down.

‘Alternate with long, easy rides that are more anabolic and therefore help strengthen the body. They’ll actually help you cope better with intervals.’

This type of training has also been heralded as a great way of burning calories, but you have to get it right.

‘Assuming you want to shed fat not muscle, you’re unlikely to be using fat as fuel for any short intervals, whether they’re 10 seconds or three minutes,’ says Butler.

‘What interval training does do is raise your metabolism for the rest of the day – that’s why you’re starving. That’s where the fat-burning happens and, as long as you’ve gone hard in the session, the interval length is unlikely to make a difference.

‘What will make a difference is whether you satisfy that hunger with broccoli or cake.’

Where’s the evidence?

Not even science has all the answers when it comes to choosing the right intervals.

‘A lot of the research is conflicting, or even shaky,’ says Newton. ‘You might read that two minutes of rest is ideal, but on what interval? If you’re doing 10-second max efforts, a two-minute rest isn’t long enough to repeat that effort with the same quality.

‘What’s a sprinter’s favourite position?’ he asks. ‘Sitting in a chair. They roll out, sit up for a few laps, race for one lap at max effort and roll back in. Then they sit in a chair to recover – and they need more than two minutes.’

Stern takes a different view. ‘There’s stacks of evidence in research papers showing how different training regimes alter fitness – everything from very short to much longer intervals,’ he counters.

‘That said, it’s important to understand that no one session is a magic bullet, and that your performance will be affected not only by specific sessions but by your total workload.’

‘Taking a sample of cyclists and giving them different training plans over an agreed time period doesn’t really tell us that one workout is better than another – it tells us that each type of interval training is associated with unique benefits,’ argues Butler.

‘If you want to be good at going flat out for 30 seconds every minute, how could there possibly be an argument against riding like that in training? You get good at what you do a lot of.’ 

Watch - How to ace an interval session

As with so much of training, what works for you will be unique to you. ‘Different people respond better to different training so it’s worth experimenting,’ says Butler.

‘You may be able to go very deep in an interval session but need three days to recover, whereas someone else may be able to get up the next day and repeat the same session.

‘That may mean you go on to be very good at one-day events, while they may excel in stage races.’

‘Danish researchers came up with an interval that goes: 10 seconds flat out, 20 seconds hard, 30 seconds steady – not easy, but steady, so you’re still putting in an effort,’ says Newton.

‘Do that five times, rest for five minutes, do five minutes easy pedalling and then start again. Do it two or three times, but remember the point of intervals is that less is more – you should always finish feeling as if you could go again.

Why does it work? I don’t know, but what I do know is that it works for me and it works for the clients I’ve prescribed it to. Experiment, but always come back to what works for you.’

As Stern says, ‘Ultimately, if you’re increasing the power of either your aerobic or anaerobic systems – or both – that’s the most important thing.

How to complete an interval session

Completing an interval session is quite straight forward, especially when riding on an indoor turbo trainer. For a guide to the best smart turbo trainers, see here.

Start by setting your bike up, grabbing a water bottle, a towel and warming up for 15 minutes at a level just below your functional threshold power before doing the following:

  1. Maximal sprint 30 seconds, 30 sec recovery
  2. 1 minute @ 140% FTP with 1 min recovery
  3. 2 mins @ 120% FTP with 1min recovery
  4. 2 mins @ 120% FTP with 1min recovery
  5. 3 mins @ 110% FTP with 2 mins recovery
  6. 1 min @ 140% FTP with 30 sec recovery
  7. 30 sec maximal sprint
  8. Cool down for at least 10 mins

For a list of more indoor workouts you can do to make you a better cyclist, see here.

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