The fourth article in a seven part series in partnership with Verve Cycling - the official power crank supplier to the Great Britain Cycling Team - explains what is FTP, why it’s important and how to test it.
What is FTP?
Functional Threshold Power (FTP) has been traditionally defined as the power that you could theoretically maintain for an hour. However, unless you’re an extremely well trained or elite level rider, it’s better thought of as your sustainable power. This might be 35 or 40 minutes but, rather than trying to put a number on it, a good analogy is to see it as the red line on your cycling rev counter.
Why is it important?
Knowing your FTP allows you to set accurate and personalised training zones. This is vital for constructing appropriate workouts and pacing rides. Also key power based metrics, such as Training Stress Score (TSS) and Normalised Power (NP), which we’ll discuss in more detail later, are intrinsically linked to and will only be valid with an accurate FTP.
Also, on Zwift, for ensuring you’re in the right category for races, group rides and are riding at the right intensity on group and regular workouts, having an accurate FTP is essential.
Different test protocols
There are a number of test protocols you can follow to test your FTP but the key thing is to find a protocol that works for you and stick with it. Most of the protocols use a maximal effort over a shorter period of time than an hour and then apply a percentage reduction to the average power figure achieved. It can be tempting to opt for one of the shorter protocols but, as FTP is a test of sustainable output, a 20-30 minute test represents the minimum we’d recommend.
The British Cycling Threshold Test
The British Cycling Threshold Test uses a 30-minute protocol of which your average power is recorded for the final 20 minutes and then a 5% reduction is applied to calculate FTP. Over years of using this protocol with thousands of riders of all levels, from Olympians to novices, we’ve found it strikes the perfect balance between accuracy and usability.
For details of the British Cycling Threshold Test click this link.
Indoors vs outdoors
Although the discrepancy is typically less than with heart rate, there can be a difference between your indoor and outdoor FTP. However, if your ventilation and cooling indoors is good, you’re on the same bike/riding position and measuring using the same power meter, then the difference will be minimal. If these criteria aren’t met or you’re finding indoor session based on your outdoor value unusually hard, it’s probably worth performing an indoor test and setting indoor training zones. If using a smart trainer it’s important to ensure you switch to slope/level mode as opposed to ERG mode when testing for FTP.
How often to test
On the British Cycling Digital Training plans we’ll typically schedule in an FTP test every 8-weeks. However there are a number of over scenarios which might indicate that a the-test is necessary.
If you’re following FTP based workouts and you’re starting to get through them fairly comfortably, it’s probably time to re-test your FTP and to bump up those training zones.
If you track your workouts on TrainingPeaks, you’ll be aware of the Training Stress Score (TSS) metric. An hour riding at your FTP would result in a TSS of 100 so, if you manage to log over 100 in an hour, your FTP is definitely off. Also, for longer rides, TSS will typically be accumulated at a rate of about 50-60 per hour. If you’re above this, it’s time for a re-test. It’s worth noting that TrainingPeaks can be set to automatically update your FTP based on your ride data.
If you’ve had to take time off training due to injury, illness or life just getting in the way of your cycling, re-test before getting back into it again. If you don’t, you’ll probably find workouts harder than they should be, struggle to get through them and risk overtraining and demotivation. A couple of weeks off shouldn’t necessitate a re-test but any longer and it’s a good idea.
If you’re new to training with power and/or FTP testing, you might not have felt that you managed to pace the test well and squeeze every last watt out. The British Cycling Test Protocol is surprisingly robust at dealing with poorly paced tests and the impact on training zones will be minimal. See how a couple of workouts feel and, if you find the zones very easy, try a re-test.