Fuelling Indoor Training: Zwift, Turbo and Treadmill Sessions Explained

Indoor sessions have a reputation for being nutritionally simple. No wind, no hills, no pockets to rummage through, and the kitchen is ten steps away. In practice, plenty of athletes get their fuelling wrong indoors, usually by assuming that a one-hour turbo spin needs nothing and a three-hour Zwift epic needs a bottle of squash. Neither is true, and the mistakes show up as flat legs in the final third of the session or a stomach that complains halfway through.

The reason is that indoor training is physiologically harder than the same effort outdoors. There is no coasting, no descents and almost no airflow, so your core temperature climbs faster and your sweat rate can double. If you want to get fuelling indoor cycling right, you need to treat the session as a proper training day, not a throwaway one. Here is how to do it for the bike trainer and the treadmill.

Why Indoor Sessions Burn More Than You Think

Studies comparing indoor and outdoor cycling at the same power consistently show higher heart rates and core temperatures indoors, because convective cooling is so much weaker. A fan helps, but it rarely matches the airflow of riding at 30 km/h. Sweat rates of 1 to 1.5 litres per hour are normal for a lot of riders on a turbo, and some lose well over that in a warm garage.

There is also the matter of continuous pedalling. Outdoors, a two-hour ride might include 15 to 20 minutes of freewheeling. Indoors, that time is spent working. An hour of structured Zwift intervals often delivers more training stress than a lazy 90 minutes outside, and the carbohydrate cost goes with it. As a rule of thumb, a rider averaging 200 watts burns roughly 700 to 750 kcal per hour, and most of that comes from carbohydrate once you pass a moderate intensity.

How Much to Eat by Session Length

Match your intake to duration and intensity rather than the venue. These are sensible starting points for most adults:

• Under 60 minutes, easy to moderate: water is enough if you have eaten in the last two to three hours. Add electrolytes if you are a heavy sweater.
• 60 to 90 minutes, or any session with hard intervals: 30 to 45g of carbohydrate per hour, starting within the first 20 minutes.
• 90 minutes to 2.5 hours: 45 to 70g per hour, using a mix of glucose and fructose so the gut can absorb more.
• Over 2.5 hours (long Zwift races, group rides, back-to-back blocks): 60 to 90g per hour, only if you have trained your gut to cope with it.

Short, sharp sessions deserve a mention. A 45-minute threshold workout will not empty your glycogen stores, but the quality of your final intervals can still drop if you start under-fuelled. A proper meal two to three hours before, or a small carbohydrate snack 30 to 45 minutes before, usually does the job.

Fuelling Indoor Cycling: Practical Tips for Zwift and the Turbo

The big advantage of the turbo is control. You can set everything up before you clip in, so use it. Put your fuel where you can reach it without breaking cadence, ideally on a small table or the handlebars, and open the packaging beforehand. Pastilles and chews are excellent here because you can eat one or two at a time without losing focus on a workout or a race effort.

Set a reminder. It sounds trivial, but a recurring alert every 15 to 20 minutes is the single most useful habit for indoor fuelling. Zwift racing is the classic trap: the effort is so absorbing that 75 minutes pass before you realise you have eaten nothing. If a session has a hard block of intervals, take your carbohydrates in the recovery periods rather than during the efforts, when breathing is laboured and chewing is unpleasant.

Drink to a plan as well. Aim for 500 to 800ml per hour indoors, more in a warm room, and include sodium. A fluid with 500 to 1,000mg of sodium per litre is a reasonable range for heavy sweaters. Weigh yourself before and after a few sessions. If you are losing more than 2% of your body mass, you are under-drinking and your power will fall as a result.

Treadmill Sessions: A Different Challenge

Running indoors brings its own problem: you cannot easily carry or access fuel while moving, and the impact makes the gut less forgiving than cycling. For anything over 75 minutes, take carbohydrates every 20 to 30 minutes in small amounts, around 20 to 30g each time. Soft pastilles that you can chew quickly work far better than gels that need water to wash down or bars that require serious chewing at pace.

Keep a bottle on the console and a small stash of fuel within arm's reach. Heat is again the issue, so use a fan, keep the room cool and watch your hydration. Most runners find treadmill long runs feel harder than the same pace outside, and underfuelling makes that perception much worse.

What We Use at FTP Endurance Fuel

Indoor sessions are where we do a lot of our own testing, because you can control every variable and see exactly how your body responds. For turbo and Zwift work we reach for our Mixed Fruit Pastilles: they are a fixed glucose and fructose blend, easy to portion into 10g to 15g hits and soft enough to chew during a recovery interval. For a change of flavour there are the Tart Cherry Pastilles, which are tart cherry flavoured; real Montmorency tart cherry is in Power Fluids.

If you have never tried pastilles instead of gels, the Taster Pack lets you test them on a few indoor sessions before committing to a larger bag. The turbo is the perfect place to find out what your stomach tolerates.

Putting It Together

Fuelling indoor cycling and treadmill work comes down to a few habits: eat before anything over 60 minutes, take 30 to 90g of carbohydrate per hour depending on duration, set reminders so you actually do it, and replace the fluid and sodium you are losing in a warm room. Practise your plan on indoor sessions and you will arrive at race day with a strategy that has been tested dozens of times. Ready to try it? Browse our full range of bundles and build a fuelling routine that works for every session, indoors or out.