Can this workout predict your half-marathon time?

The newly coined “Fultzy 400s” session is designed to give you an insight into your half-marathon potential. But does it work?


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You might well be familiar with the Yasso 800s workout. Devised by former Runner’s World journalist Bart Yasso, it aimed to offer an accurate prediction of your marathon time based on a relatively straightforward track workout. You run 10 x 800m and your time in minutes per rep is meant to correspond with your time in hours for the marathon.

For instance, if you ran your 800m reps in 3mins 30secs, you may be able to run a 3hrs 30mins marathon. The time between reps should be kept the same as your rep time (in the case above, 3mins 30secs). It’s by no means a perfect formula. Many commentators think that it’s entirely possible to nail a Yasso 800s sessions but fail to run a corresponding marathon time. Coaches also point out that the training for, and ability to run well, at middle distances is very different to the requirements to nail a marathon time. But regardless, Yasso 800s remains a classic workout – and now there may be an equivalent for the half-marathon.

This one has been coined the “Fultzy 400s” by legendary running author and marathoner Amby Burfoot, in homage to 1976 Boston Marathon winner Jack Fultz. The workout involves running 20 x 400m, with a 60-90-second walking recovery between reps. If you’re planning on running a 1hr 45min half-marathon, your aim is to run the reps in 1mins 45secs. If it’s a 1hr 30min half-marathon you’re after, run the reps in 1min 30secs. You get the idea.

But is it actually an accurate predictor of half-marathon time? Former elite marathoner and running coach Jo Wilkinson isn’t so sure. ‘I think it’s hard to extrapolate race predictions from one session alone,’ she says. ‘It’s always an attractive idea. But the best indicator of race times is training as a whole.

‘I think the challenge of Yasso 800s versus Fultzy 400s is the pace you would run the Fultzy session is significantly harder. In physiological terms, the Yasso formula equates closer to threshold pace, which is a better predictor of marathon (and half marathon) times. On this formula, by contrast, you are running at a pace closer to your pace at vo2 max (or even above subject to your HM time), which is much faster.

‘There is some correlation between vo2 max and pace at vo2 max with HM times. But much less correlation than there is between threshold and marathon. What’s more, it makes it a very tough workout.

‘So I wouldn’t necessarily recommend basing your HM pace on this session because the pace is quite hard. However, if you nail this session, you probably are in great form – and maybe should revise your ambitions too.’

Whether or not either workout can really accurately predict your race times, it’s certainly the case that they are both great training sessions in their own way, and as long as it’s not too close to race day, it’s definitely worth giving them a go.

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