Indoor trainer: how to improve this winter

In winter, many riders move to the indoor trainer and ride hard in every session, often in front of a video. After a few weeks they are tired and no faster. Here is how to organise your indoor sessions so that winter makes you faster.

Why ride the indoor trainer in winter?

In winter, rain, cold and early nightfall make you skip rides. The indoor trainer lets you keep riding anyway, in slots of 45 minutes to an hour during the week.

It also helps with intervals. With no red lights, descents or traffic, you hold your efforts at the planned power from start to finish.

It doesn't replace the road, though. Keep your long rides outside at the weekend, when the weather allows.

Is 250 W on the indoor trainer the same as 250 W outside?

The power is the same, but the effort is harder indoors. Here is what changes.

Because you never stop and you are hotter, an hour at the same average power tires you more on the indoor trainer.

That is why many coaches count an hour of endurance on the indoor trainer as 1 h 15 to 1 h 30 outside. If you move an endurance ride indoors, you can shorten it. Intervals keep the same length and the same power.

Finally, your indoor trainer and your power meter don't always read the same. If they are 10 W apart, pick one and always use the same one to compare your sessions.

Which mistakes stop you improving on the indoor trainer?

The same five come up almost every time.

For the first three, the simplest fix is to plan your week in advance. Decide which day you do each session and what it should work on, and put an easy day after every hard session. In the evening, you just ride what is planned.

To check whether you drink enough, weigh yourself before and after a session. The American College of Sports Medicine advises not losing more than 2 % of your body weight during exercise, which is 1.4 kg for a 70 kg rider. If you lose more, drink more next time. For food, count the same carbohydrates per hour as for a ride outside.

Does a fan make a difference?

Yes, a big one. In a study published in 2023 by Fernandez and colleagues, 16 adults rode 40 minutes indoors at the same heart rate, with and without a fan. With the fan, they produced 15 % more work on average, and they felt cooler.

That figure holds for the conditions of that study, but the principle is the same at home. Without airflow, your body spends energy cooling down, and it has less left for pedalling.

You can check it on your own sessions. During a block of at least 20 minutes at steady power, watch whether your heart rate climbs as the minutes go by. If it climbs mostly on days without a fan, the heat is holding you back.

FTP, CP or lactate test: which number should you train on?

All these tests estimate your threshold, the power above which fatigue comes very quickly. You then use it to work out your training zones.

You can do FTP and CP tests on your own, with a power meter or a smart trainer. The lactate test and the lab test measure what happens in your body directly, but they need equipment or an appointment.

The indoor trainer is a good place for these tests in winter, because there is no wind and no junctions. Always repeat them on the same trainer and in the same way, so you can compare your results.

Which zones should you use?

Once you know your threshold, you can work out your zones. Here is a common split into seven zones, as a percentage of your CP.

For example, with a CP of 260 W, your zone 2 runs from 138 to 190 W.

Which sessions should you ride on the indoor trainer?

Give each session one goal, and choose it before you get on the bike: endurance, threshold, VO2max or sprint. Here are three examples.

With a smart trainer, you can use ERG mode. The trainer then sets the resistance so that you stay at the planned power, whatever your cadence. It works well for threshold or endurance blocks. On very short efforts it takes a few seconds to adjust. For those, switch to free resistance and control the power with your gears, as you would outside.

What does a realistic week look like?

Here is an example 7-hour week for a sportive rider who is already used to training.

The two hard sessions are on the indoor trainer during the week, when you are short of time and want to hold precise power. A rest day separates them. The long endurance rides are outside at the weekend.

If 7 hours is too much for you, cut some volume, for example by shortening the endurance rides. A lighter week that you finish will make you faster than an overloaded week you give up halfway through.

How do you choose tomorrow's session?

Look at four things before you decide.

• Your form: how you slept, how you feel, how tired you are.

• What you did over the previous days.

• The time you have: 30 minutes, an hour or two hours.

• Your goal: a sportive, a climb, more power.

If you missed a session, don't make up for it by doing two the next day. Move it if your week still has an easy day before the next hard session. Otherwise, let it go.

Your watch can help too. If you sleep badly, or if your resting heart rate stays higher than usual for several days in a row, that is often a sign of fatigue. If you are ill or have an unusual pain, stop and see a doctor.

What should you do in your next session?

1. Put a fan in front of you, at full speed, and a bottle within reach.

2. Before you start, write in one sentence what the session should work on.

3. If your last hard session was yesterday, ride easy today.

Sources

• Fernandez et al., Research Quarterly for Exercise and Sport, 2023, doi:10.1080/02701367.2021.1946467: 16 adults, 40 minutes of indoor cycling at 70 % of heart rate reserve, with and without a fan.

• Jones A. M. et al., "Critical power: implications for determination of V̇O2max and exercise tolerance", Medicine & Science in Sports & Exercise, 2010, 42(10): 1876-1890.

• "Perspective on HIIT", Sports Medicine, 2024.

• Sawka M. N. et al., "American College of Sports Medicine position stand: exercise and fluid replacement", Medicine & Science in Sports & Exercise, 2007, 39(2): 377-390.

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