Rate of Perceived Exertion (RPE)
Many triathletes and cyclists will find that given a particular heart rate or power production, RPE is much higher indoors than it is outside. This perception could be caused by higher indoor temperatures and lack of air flow.
Another theory is that riding on an indoor trainer requires fewer muscles, because you don't have to balance yourself. With fewer muscles working, you need to work harder to produce a given heart rate. While I've never seen a study to confirm it, some coaches believe that these balancing muscles also contribute to power production. If that's the case, then with fewer muscles engaged it's tougher to produce any given heart rate or power level.
Finally, some people believe it's just not as interesting to ride inside and that makes it feel harder.
What all this means is that you may need to adjust your intensity zones down slightly for indoor sessions.
Tempo and Threshold Sessions
If your aim is to improve your tempo riding speed, hill climbing ability or lactate threshold speed, then it's best to have some structure to the workout. I like a warm-up, a main set and a cool down.
A lot of people think that improving lactate threshold speed, means all sessions need to be 20 minutes of steady effort. But broken intervals and even very short intervals can improve threshold speed and power production.
Improve Power
If you want to put your head down and produce huge amounts of power for a short duration, inside is the place to do it. You don't have to worry about accidently weaving into traffic, hitting a pothole, or having an animal or human dart in front of you mid-effort.
Improve Cycling Technique
Some people think that cycling doesn't require any special technique. After all, you just spin your legs in a circle, right?
It was Lance Armstrong that made high cadence riding popular. While many other top cyclists in his era used big gears and low cadence, Armstrong worked on higher rpm.
Do both of your legs produce equal power and are they both smooth and efficient? If not, you can gain benefit from doing drills to improve your technique.
Make it Count
With some planning and forethought, you can take what could be a boring indoor training session on the bike and turn it into one of your key sessions for the week. These sessions add up over the course of a few weeks and can make a significant impact on your goals.
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