The key to training effectively is riding at different intensities depending on the purpose of the workout. Your intensity shouldn’t be the same if you are training for endurance or for power or for speed or doing an active recovery ride. This applies whether you’re riding outdoors or on the trainer. To train at different intensities you need a way to gauge intensity and a method to define the different levels of intensity, i.e., a set of training zones.
However, your training zones on the road may not transfer directly to the trainer.
Ways to gauge intensity:
Perceived exertion is the simplest, requiring no equipment. It means learning to listen to your body. Lab studies show that perceived exertion is as effective a way of tracking intensity as heart rate. This is how I train.
A heart rate monitor tells how fast your heart is beating. It is an indirect way of measuring how hard your muscles are working because it’s looking at the input to your muscles. Heart rate may be inaccurate because it is determined not only by how hard your muscles are working but also by how well you slept, if you are excited or stressed, how hot it is, what you ate (e.g., sugar, caffeine), if you are dehydrated and other factors.
A power meter measures the wattage you produce at any given instant. It is a direct way of measuring how hard your muscles are working and is the most accurate method, but it requires the most specialized equipment and learning how to interpret complicated data.
Which method of gauging intensity is best for you depends on your goals. If you have a high goal, for example being competitive in age group racing, then you need very accurate feedback on intensities when you train so you’ll find a power meter very helpful.
If you are training for good performance, for example on club rides, but aren’t racing, then either perceived exertion or a heart rate monitor is fine. If you ride for recreation then perceived exertion is the way to go.
The right method also depends on your personality. Some people like data and keep extensive training logs, some people don’t care for numbers. Data alone are useless. If you like numbers and can interpret them (or have a coach who can interpret them) to provide useful information, then you may want to use a heart monitor or power meter. If numbers don’t mean a lot to you then stick with perceived exertion.
Here’s a column on The Benefits of Training by Intensity.
Gauging Intensity on the Trainer Isn’t the Same as on the Road
Conditions may be different when you’re riding your trainer. For example, you’re probably getting hotter for the same level of effort than you would riding on the road.
For perceived exertion to be accurate you need to focus on two indicators: how rapidly you are breathing and what your legs feel like. When you’re hot on the trainer it’s harder to ignore the general feeling of discomfort and focus on the two meaningful indicators: your breathing and your legs.
When you get hot your heart beats faster to circulate more blood to your radiator, your skin. On the trainer your rate monitor may read higher than on the road for a given level of effort. You can offset this by putting a big fan in front of the trainer. Better yet, do your training in the garage in cooler weather with the door open.
If you train by power, it’s not affected by how hot you’re getting. However, there are still differences between power on the road and power on the trainer. Most cyclists can produce more power on the road than on the trainer. Here’s a good explanation. Equipment also makes a difference. Although smart trainers often claim that the power reading is the same as on the road this often isn’t true. You can mitigate this by using the same equipment the trainer that you use on the road: the same bike and the same equipment to gauge power (e.g., Garmin, Stages).
Training by Zones
6 Kinds of Intensity Training: Which One is Best for You? explains the different training zones and which zones you should use depending on your personal objectives.
How Cyclists Should Approach Intensity Training for the Maximum Benefit describes how to set your own training zones and then explains the principles of training by intensity.
You can download a spreadsheet to calculate your training zones here.
My eArticle Intensity Training: Using Perceived Exertion, a Heart Rate Monitor or Power Meter to Maximize Training Effectiveness explains in more detail your physiology, which type(s) of intensity training is right for you and how to do intensity training including whether RPE, heart rate or power is best for you. The 41-page Intensity Training is only $4.99.
Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.
Power should not vary much indoors vs out. You absolutely should not get into the mindset that being on the turbo is “harder” and use this an excuse to go more easy and reduce target watts. Muscles respond to real watts and will just get weaker if you do.
If you feel there is a difference it will mostly be down to not having enough cooling so get more fans.
The other main cause will be mental, there is more to keep the mind occupied when riding outdoors which is why platforms like Zwift are so much more fun than staring at a blank wall.
If you do not own a power meter then you should fit speed sensor to your rear wheel and use that as an independent measure to judge RPE and HR against. Aim to go a little faster or further each session. This can work very well, Graeme Obree used it as a method to train for his record breaking hour ride,
I recently read that the oxygen levels inside a building are much lower than outside. Could this have anything to do with it?