Why is my indoor power lower?
Can’t match your outdoor output? It could be one – or all – of these things…
There are a number of reasons why you can’t produce as much power indoors on a turbo as you can on the open road, and the biggest one is purely a matter of mechanics – a turbo applies resistance through the entire pedalling circle, whereas there’s no significant resistance at the bottom and back of the pedal stroke on a road bike. This is 90% of the reason your watts are lower indoors.
Think about how you ride as well. On the turbo you’re essentially ‘locked’ into a single position, and we create effective watts by using our upper body as we ‘wobble’ the bike outdoors. Indoors, it’s very difficult to use all of your collateral muscles.
Heat is another big factor. Indoors you will get hot, whereas outdoors you will at the very least have more of a breeze and fewer walls hemming you in. The cooler your body, the higher the wattage you can maintain. Then there’s the mental aspect – going nowhere fast. I’d say this is huge. Most cyclists I know love to ride because they love being outside, going to a cool location and riding at maximum speed. There’s great satisfaction in being able to travel long distances under your own power. I’ve seen some beautiful ‘pain caves’ and that is at least a great way to help stay motivated, but it’s still not the same as riding outside at 50kmh with the wind in your hair.
One other thing to consider is where you are measuring your power output. It can be measured in multiple places on your bicycle, but the closer the measuring device is to where the power is being transferred from your foot to your bike, the more accurate the reading. If you measure power in your rear wheel, you’ll lose
7-10 watts from inefficiencies in the drivechain system. So 250 watts at the pedal is probably 240 watts at the hub of your smart trainer.
Then there’s your bike. If you can mimic your exact fit from your bike to your indoor trainer, you should be able to produce the same watts, right? But there’s also this thing called gravity, and virtually everyone will produce more power outside while climbing (seated or standing) than on the trainer. Gravity is a powerful form of resistance and the ability to stand and climb or stay seated and use your entire body to help push down on the pedals is significant compared to just riding in the saddle on a trainer. One British racer I coached could only hold 300 watts at his FTP on the flats, but put him on a climb and his FTP was 360 watts.
The turbo trainer does have its place. Of course we are tough endurance athletes so you’d better be able to overcome any negative self-talk or you might find needlework is a nice hobby… but it does take practice and it takes purpose. What is your goal and why do you want it more than anything else? I ride indoors because I’m doing specific intervals that I just can’t do outside, racing in Zwift or coaching a client over Trainerroad. All of those are motivating factors for doing my best.
So there are benefits. Working out indoors has always been a very effective way to train. You have fewer distractions, no traffic, no stop signs. You can do perfect intervals every time and address the correct energy system with no guesswork. It can help you produce more power, full stop – whether it’s higher or lower indoors or outdoors doesn’t really matter as long as your power output is going up.