Using a Power Meter for a Triathlon by Aidan Rich @ 20 Nov 2017
Part One – Introduction and Training
This article is designed to be a ‘quick and easy’ guide on training with a power meter. If you want lots of detail, I’d recommend buying the book ‘Training and Racing with a Powermeter’ by Allen and Coggan. In terms of choosing which powermeter to buy, have a read through some of the articles by DC Rainmaker (dcrainmaker.com). I use a powertap laced into a rear wheel which I can use for training and racing. Other popular choices include Stages (crank based) and Garmin Vector or Powertap P1 (both pedal based).
So you’ve installed your power meter, what’s first? It’s worth changing the display settings on your watch or cycling head unit so you can see how much power you are generating. The four settings that I display when I’m doing efforts (or in a race) are:
• 10 second power
• Lap time
• Lap distance, and
You can also use 3 or 30 second power but I find that they are either too responsive (3 second) or not responsive enough (30 second).
Next thing – just go for some rides! Watch how your power spikes on a short uphill, is lower when drafting, and feel how hard it is to hold high power on a slight downhill. The power on the head unit should represent how much pressure you can feel between your feet and the pedals.
After that, it’s time for testing! The best test to do is to measure what’s called FTP, of Functional Threshold Power. This is how much power you can maintain for about (not exactly) one hour in a maximal effort.
There are a few methods of FTP testing but the most accepted is by Allen and Coggin, which involves:
• Warm up
• 5 mins very hard
• 10 minutes very easy
• 20 minutes MAX
A couple of notes on how to best do this
• Be rested e.g. 1-2 easy days prior
• See it as a training session (“testing is training, training is testing”)
• Do it somewhere where you won’t be distracted by traffic. A velodrome is best, a long flat road in the country would also work. Up a 20 minute hill generally gives higher numbers than flat, and a trainer (indoor bike) generally gives lower numbers.
Your FTP is 95% of the 20 minute figure. So say you averaged 211 watts for 20 minutes, your FTP would be 200 watts (a nice round number to use for this piece).
This becomes the number that you can use to guide your training sessions, some examples of what could be done:
• Vo2max intervals (great for increasing FTP): 6 x (4 minutes at 110-115% of FTP, 3-4 minutes very easy), so 220-230 watts in this example
• ‘Sweet spot’ intervals (good ‘bang for buck’ for cycling fitness): 2 x (20 minutes at 88-92% of FTP, 5 minutes very easy)
• 70.3 sim ride: 2-3 x 20-45 minutes at 70.3 power (this will be 70-85% of your FTP depending on your fitness, e.g. a front of pack triathlete may only take 2hr 15 minutes for the 90km ride so can ride at a higher intensity, and a mid-back of pack athlete may be 3-3.5 hours, so will ride at a lower intensity
• Ironman sim ride: 5.5-6 hours as: 2 hours easy, 2 x 90 minutes at Ironman power (10 min easy between), 1 x 60 minutes at 70.3 power, cool down
It’s worth retesting your FTP every 6-8 weeks or so, a really good training block may see it change significantly. The exact sessions depend on which phase of your training you are in, as well as your fitness and target races.
After a while you’ll start to see where your race efforts will fall, e.g.
• Sprint (20km) ~100% of FTP
• Olympic (40km) 90-95% FTP
• 70.3 (90km) 70-85% of FTP
• Ironman (180km) 60-75% of FTP
For context around FTP, elite male triathletes are around 5 watts per kilo (so 350W for a 70kg athlete). Males 25-45 who qualify for Kona are typically 4.1+ watts per kilo (so 287+W for a 70kg athlete).
The other terminology I’ll introduce now is ‘Average Power’ (AP) and ‘Normalised Power’ (NP). Average power is a strict average of your power over a given time, while normalised power is ‘what your legs feel’, i.e. a representation of the effort of the ride. Here is an example to show the difference:
• John rides for 1 hour on a completely flat road. He holds 150 watts the entire time. His Average power is 150, and his normalised power is also 150
• John rides a small hilly loop for an hour, where he rides uphill at 250 watts but downhill at only 50 watts. His average power is still 150, but the effort of this ride is a lot higher, and the normalised power (which would be about 180) reflects this.
For most triathlons on flat courses with minimal wind, your average power and normalised power should be very close together. On hilly/windy courses, it’s fair to see a slightly larger difference.
The term ‘Variability index’ (VI) shows the difference between the two. Variability index equals normalised power divided by average power, e.g. normalised power of 210 divided by average power of 200 equals a variability index of 1.05. Most triathlons should see a number of 1.05 or below.
In terms of how to analyse your power files, strava and garmin connect both give some good information. To see more you need either Training Peaks (a paid service) or Golden Cheetah (free).
Especially with long course racing, there is a ‘fine line’ with how hard to push on the bike. Every second you spend about 95-100% of FTP has the potential to hurt your run performance. But more on racing with a powermeter in the next article!
Part Two – racing with a power meter.
You’ve done the training and you’re ready to race! How can a powermeter help you to execute your perfect race? Read on…
Sprint race (20km) – turn the power meter off! Or at least don’t worry about checking the numbers. A sprint race should be pretty much as hard as you can go! It does give good data to look at after, often in the heat of competition you can produce higher numbers that you ever could in training.
Olympic distance race (40km) – remember the target for this is likely to be about 95% of your FTP (so 190 watts in our example). It’s probably wise to avoid sustained periods above 110% of FTP (220 watts), so perhaps just keep an eye on the 10 second power and make sure you’re not going too crazy, especially in the first half of the ride.
70.3 race (90km) – here is where the power meter really becomes valuable. Ideally you should look at gradually building power throughout the ride, as well as avoiding periods above FTP (this will hurt your run). For someone with an FTP of 200 watts, they may look at averaging 150 watts for the ride (your training will allow you to determine an exact target). Perhaps split the ride into thirds, e.g. 30km at 140-150 watts, 30km at 145-155 watts and 30 km at 150-160 watts. This enables you to build through the ride and finish strong. If you are feeling great midway through the ride, you can adjust towards the higher end of the range. There is no easier way to destroy your race than spending the first 30km at 20+ watts above goal power – this cooks your legs and makes it hard to get valuable nutrition in!
Ironman race (180km) – the guidelines are similar as the 70.3 race, but patience and diligence to following a plan is rewarded even more. Again, split the ride into thirds and aim for slightly increasing power throughout the ride. Especially on a flat course, limit periods above 90% FTP, this will hurt your marathon (it’s a long way to run on beat up legs!). Keep the head down, keep your eye on the power and try and keep it as close to target as possible. I look at 10 second power and also use ‘auto lap’ every 10km to monitor power of the course of a 10km segment. Ironman power will feel easy in the first hour or two but becomes a real challenge after 130km or so!
A few more tips for racing:
• (legal) drafting. Sitting 10-12 metres behind someone is typically about 10-20 watts less power for the same speed. If you are aiming to hold 160 watts, and holding 155 sitting 10-12 metres behind someone, it’s probably wise to stay there. The benefit is greater into a headwind and less with a tailwind
• Hilly courses. This is tricky! It’s better for your race time to go a bit harder uphill and a bit easier downhill. There aren’t a lot of long hills in any 70.3 or Ironman race in Australia that I’m aware of. You might push up to 90-100% of FTP for short hills (1-3 minutes) in a 70.3 (higher for fitter athletes) and 80-90% of FTP for short hills in an Ironman (again higher for fitter athletes). You’re rewarded by a slightly reduced effort on the downhill!
That’s enough detail for the scope of these two articles. There is a lot more to learn including performance management charts (PMC), Training Stress Score (TSS), Chronic Training Load (CTL), Acute training load (ATL), Training Stress balance (TSB), Intensity Factor (IF), Quadrant Analysis… I could go on and on! However being comfortable with the content from the two articles I’ve written is well and truly enough to get you using a power meter effectively.
I’m happy to give more specific advice if anyone wants to contact me, and there is also the book I referenced in the first article if you’re keen to learn more. Alan Couzens is an Australian physiologist who has produced some excellent articles on triathlon and power (alancouzens.com)
Happy (and smart!) racing