Is winter mileage a thing of the past? Here’s why coaches are replacing long outdoor rides with short indoor intervals

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Cycling fitness used to be visualised as a pyramid. You started by building a solid, broad base of easy and steady-paced riding, then, brick by brick, you added aerobic endurance, harder efforts and finally the pyramids peaked with maximal power and race-specific preparation. Then, after a taper, you were ready.

This is known as periodisation, and the principles behind it haven’t changed in decades. According to Hunter Allen and Andrew Coggan in their seminal Training and Racing with a Power Meter, “the principles that Dr Tudor Bompa – the so-called Father of Periodisation – put forth back in 1968 still apply today: You have to build, taper and rest in order to create an overload and then allow for an adaptation to that new level of stress.” So an athlete’s annual training plan was divided into periods, with these periods splittable into phases – macrocycles and even smaller microcycles.

In the northern hemisphere the road cycling season runs roughly from March to October, which means that if following a traditional programme of periodisation, riders would need to start laying the foundations of the pyramid in November, building mileage through December and January. The problem is that this is the time of year when the days are at their shortest, the temperature is at its lowest and the roads are in their most potholed and dangerous condition. In the olden days, this phase might have been regarded as ‘character building’. The mental toughness might have come in handy if you wanted to win Liège-Bastogne-Liège in the snow, for example. If it really was too icy to ride outdoors, something even more character-building lurked in the garage: the turbo. An instrument of torture into which you would clamp your bike and yourself and endure a uniquely unpleasant mix of pain and boredom. 

But 10 years ago, all that changed with the advent of Zwift. Suddenly indoor training was not a distant second but instead offered clear advantages over its outdoor counterpart. There were no cars, traffic lights or potholes in Watopia, no punctures or other mechanicals, and riders were not at the mercy of the elements – there was nothing to interrupt your intervals or expose you to the potential dangers of a hostile environment. Zwift not only eliminated those risks but also added unexpected fun and excitement to indoor training with its bright virtual worlds and winding roads packed with the avatars of riders coming together from all over the globe to train, race or just ride.

Could these benefits not be harnessed so that the high-intensity training and racing indoors on Zwift took place during the winter months, postponing longer outdoor endurance rides for when the sun comes out and the days get longer? In other words, could you safely build the pyramid in reverse, from the top down, and reach the same level of fitness? Sports scientists, coaches and riders immediately set themselves to the question. And the answer was yes.

A Norwegian study by Sylta et al published in 2016 in Medicine and Science in Sports and Exercise compared the effects of three different high-intensity training (HIT) models, balanced for total load but differing in training plan progression. Sixty-three cyclists were randomised to three training groups and instructed to follow a 12-week training program consisting of 24 interval sessions, a high volume of low-intensity training, and laboratory testing. The increasing HIT group performed interval training as 4×16 minutes in weeks 1-4; 4×8 minutes in weeks 5-8, and 4×4 minutes in weeks 9-12. The decreasing HIT group performed interval sessions in the opposite order as the increasing HIT group, and the mixed HIT group performed the intervals in a mixed distribution. Pre- and post intervention, cyclists were tested for mean power during a 40-min all-out trial, peak power output during incremental testing to exhaustion, VO2peak, and power at 4mmol/L lactate. All the groups improved by 5%-10%, leading the researchers to conclude that “organising different interval sessions in a specific periodised mesocycle order or in a mixed distribution during a 12-week training period has little or no effect on training adaptation when the overall training load is the same.”

Another study by Ronnestad et al looked into the effect of ‘block periodisation’ on trained cyclists over a shorter four-week period – front-loading the high-intensity training into the first week. And they found that completing the HIT before the LIT in a short cycle led to more improvement than doing it the traditional way. For the ‘block’ group, the first week constituted five sessions of high-intensity aerobic training (HIT), followed by three weeks of one weekly HIT session and a focus on low-intensity training (LIT). Another group of cyclists performed a more traditional organisation, with four weeks of two weekly HIT sessions interspersed with LIT. Similar volumes of both HIT and LIT were performed in the two groups. The researchers found that the block periodisation group increased VO2max, peak power output and power output at 2mmol/L lactate whereas no changes occurred in the traditional group. They concluded that “block periodisation of training provides superior adaptations to traditional organisation during a four-week endurance training period, despite similar training volume and intensity.”

So how might these findings translate into real-world applications?

A racer who might have at one time been given the traditional linear periodisation programme is British multiple national time trial champion Kate Allan. Having just finished her 2024 season, in which she won four national titles, she would traditionally have been resting and heading into the preparation phase of mileage in zone one, but her coach Matt Bottrill is keeping one session of intensity to keep up Allan’s VO2max while focusing on strength and endurance – torque work to increase strength and also pedalling efficiency. She’s keeping volume up in zones two and three but, says Bottrill, Allan is training in “different zones so we can be consistent”. And, crucially, Bottrill says he “always structures training based on how you’re adapting to the training given.”

Dr Auriel Forrester of Scientific Coaching has 40 years of coaching experience, a PhD in human physiology and is a former international rider and multiple Masters world champion. She agrees that good sense has been prevailing over misguided heroism recently. Fewer people are doing six-hour rides in sub-zero temperatures, but she’s seeing another advantage to Zwifting over and above simple safety and comfort. Dr Forrester firmly believes that since the first element of a rider’s form to disappear when they finish their season is top-end speed and power – the peak of the pyramid – there’s a lot to be said for continuing high-intensity interval training through the winter. “Use it or lose it” is how she sees it. The next element of fitness to disappear, or at least start to decrease, is functional threshold power. As regular Zwifters know, it takes a lot of work to get it back. However, the base of the pyramid, the endurance, is relatively easily replaced even though it takes time to put in the miles – and that is best done when the weather warms up and the days get longer.

Five years ago Dr Forrester was advocating for ‘reverse periodisation’ –  high-intensity intervals during the winter and then adding the endurance in spring – but says that since 2020 everything has changed.

“Since Covid I’m not seeing so many people training for a season of British Cycling races or CTT time trials. Many riders want to stay fit all year round so that they can target Zwift challenges in the winter and then perhaps go to the Alps in the summer – sometimes they’ll only decide to ride an event two or three weeks before. So since they’re not prioritising a year in advance, I would say there is less periodisation. A lot more coaches are giving their clients a more rounded program across the whole year: you might have a HIT session every week and also a stamina session every week. You might have a rest and recovery session too and the progression comes through those individual sessions.”

Dr Forrester reports that whereas five years ago Zwift might have been used as a safer, more engaging and more dependable way to perform intervals or races in the winter, what it offers now is an end in itself for many of her clients. “I ride with PACK on Zwift and we get 400-500 riders. We ‘sweep’ beginners on the no-drop rides; just like in the real world they’re getting dropped but then they’re not getting dropped, and then they’re winning sprints They’ve been able to finish a 1.5 W/kg than a 1.8 then a 2.1, then they do a couple of Zwift races and move up the categories. That’s where the competition is for many cyclists now – It’s about XP points and levelling up on Zwift. It’s not about winning a club 10 any more. The sport is evolving.”

However, says Dr Forrester, the fact that riders want to stay fit all year round makes her life as a coach more challenging compared with when everyone was training for the same outdoor racing season. “You’ve got to almost secretly apply periodisation,” she says. "If in the short term someone might be going to Mallorca for a 10-day trip we’ll build them up for those long rides, then put in a few easy days and then they go and do it. You’ll have an easier week when you come back, but not so easy that you lose all your gains. It’s a far looser framework because we don’t have a race season, a recovery season and stamina season like we did in the olden days or when reverse periodisation did it the other way round more recently.”

However, what hasn’t changed is the understanding – as evidenced by the ‘block periodisation’ study – that it’s possible to speed up a rider’s training adaptation for a fast-approaching event by prescribing high-intensity intervals. On top of that is the proof that interval training throughout the year preserves hard-won threshold and peak power. And finally, says Dr Forrester, “my rule of thumb has always been that two hours indoors is equivalent to three hours outdoors, because you don’t freewheel or stop at traffic lights, so the training stress score is higher. However, if you told me 20 years ago that I would spend three hours on the ‘turbo’ I’d have laughed at you, but now I’ll happily spend three hours on Zwift chatting on Discord. It’s like going out on a club run without potholes and manic drivers.”

Zwift has recently expanded its range of hardware to make indoor training even more accessible. The revolutionary Zwift Ride smart bike is an all-in-one indoor cycling setup that's designed for ultimate simplicity: it can be assembled and adjusted for multiple users with a single tool that stows away on the frame. The Zwift Ride comes bundled with a Wahoo Kickr Core Zwift One trainer or separately so that you can select your own from a range of compatible units. Outside of Zwift's own product range, virtually every smart trainer and smart bike on the market is compatible with Zwift. You could could opt for the high-end Wahoo Kickr Bike or use a much lower-priced trainer such as the Wahoo Kickr Core with your own bike.

So when you're faced with freezing fog on a Sunday morning, you can be safe in the knowledge that hitting Zwift instead of heading out into the gloom will light up your training programme in all senses.