How can power meters help you perform better?

Riding with power and mastering the zones are key to establishing a swifter triathlon bike split. Here’s our guide to wattage, learning the zones and maximising your power meter

Credit: The Secret Studio

Porsche is well versed in horsepower, but it’s far better known for tuning car engines than human ones. Yet tucked away in its ‘Experience Centre’ at Silverstone, where excitable car enthusiasts prepare to tear round a purpose-built race track in souped-up sports cars, you’ll find its Human Performance Lab, where clients are put through their paces aboard the resident Wattbike indoor trainer.


We’ve been training with a Wattbike during the season, using training zones devised from a 20min threshold test. It’s an effective solution, but obviously comes up short compared to Porsche’s lab-based offering. In the home test you pedal as hard as you can for 20mins and subtract 5% from your average wattage, which gives you an estimated Functional Threshold Power or FTP – the power you can notionally sustain for between 45 and 60mins. With this figure you can work out training zones, and by riding within each zone you can work at increasing your triathlon endurance and delaying fatigue.

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To get true power zones, blood lactate should be directly measured, and it’s in labs like Porsche’s where it’s possible to do so. Under the watchful eye of its resident sports scientist Eliot Challifour, a former pro triathlete who coaches, among others, McLaren F1 driver Stoffel Vandoorne in his physical training, we were able to do just that.

Porsche is able to run the full gamut of physical tests, but we opt for the lactate threshold and body composition tests – essential touchstones for building an effective power training plan. The former monitors the level of lactate in your blood during increasing exercise intensities and finds your aerobic (AT) and lactate (LT) thresholds. The latter uses the InBody720 body analyser to accurately measure your fat and muscle composition, giving you a starting point to improve triathlon performance by working on diet.


The lactate threshold test had us on the Wattbike, beginning at 150 watts and increasing 25 watts every three minutes. Heart rate is monitored, and fingertip blood samples are taken in the final minute of each intensity. Lactate levels are analysed as you go, and the intensity at which these thresholds occur provides an important physiological measure of your endurance capacity. It’s a fairly stressful test – although not as painful as a VO2 max that takes you to your aerobic limits – but does work you for longer. Lactate threshold tests are about how much of your limit you’re tapping into, ending before you’re totally fatigued.

Ours lasted for 24mins, taking us up to 325 watts and the point at which our blood lactate went off the chart at 9.3mmol/l. At this point, total fatigue isn’t far away as the lactate production far exceeds the body’s ability to remove it.

Our aerobic threshold (AT) was 141bpm and 208 watts (2.64w/kg) and our lactate threshold (LT) was 171bpm and 263 watts (3.33w/kg). This gave us our heart rate and
watts figures for each of the six categories within both aerobic and anaerobic systems:

Zone 1 (recovery) <55% FTP
Aiding the recovery process, this is training at an easy pace on low resistance. It increases bloodflow to muscles and reduces passive stiffness, helping you to recover faster for your next hard session.

 Zone 2 (base endurance) 56-75%
Aids the development of the aerobic system, as well as improving its efficiency (for example, improved use of fat as a fuel source).

 Zone 3 (tempo) 76-90%
Still mainly aerobic, done in timed blocks with consistent pacing. It’s more demanding than base, and

her-intensity training above aerobic threshold.

 Zone 4 (lactate threshold) 91-105%
Sustainable for around two hours in trained individuals. Interval training here increases this threshold, so increases speed that can be sustained for a given effort. It’s demanding and needs to be balanced with recovery sessions. Aim for one to a maximum of three sessions per week.

 Zone 5 (race tempo) 106-120%
Intensities sustainable up to one hour. Short interval work is a good training tool.

 Zone 6 (max effort) > 121%
Intense anaerobic efforts. Less than 15secs can improve peak power, or a few minutes to work on VO2 max.

Working at zones 2-3 on longer outdoor rides will delay the onset of your AT, while zones 4-6 does the same for LT, during interval sessions practised best on an indoor trainer. Ideally, we’d visit the lab regularly to go through the process again, having committed to a training plan devised by Eliot or the free plans on Wattbike’s website.

Repeating it is expensive and time consuming, yet mimicking the test at home using heart rate and Rated Perceived Exertion, from 0-10, is achievable. Power meters aren’t über-cheap, but to make them more than an expensive trinket these tests are a crucial starting point, providing data that motivates you to push against.

Why use a power meter?

While heart rate measures your body’s response to a workload, power meters show the workload you’re putting out, or how hard you’re pushing on the pedals. This will help you to track and measure your progress over time far better than other training tools.

Back in the day you had only a couple of options when it came to buying a power meter and they didn’t come cheap. But the big players, like SRM and Powertap, now have competition from other brands such as Stages and 4iiii, which has driven prices down. They’re still not exactly cheap (with the tech on the facing page starting at the £379 mark and going up to north of two grand), but there are now enough options out there to fit nearly every bike and funny bottom-bracket standard, making them more accessible.

Using a power meter means you can make every ride count, providing information like what training works best for you – for example, cutting out junk miles – and refining your rides and routes to stimulate the desired physiological adaptation. With access to a mine of ride and race data to pour over, if you’ve slipped off the pace or not had the fitness to hang on, you’ll be able to make an accurate judgment and adjust your training accordingly.


Probably the greatest development in power meters has been in managing fatigue and form to peak for races, but its key sell is flexibility.  “There’s no one proper way to use our system,” says analysing and coaching software TrainingPeaks founder Dirk Friel. “Each athlete and coach has a different methodology. Did the triathlete hit peak power values today? How hard was the ride? Where’s your fatigue score?”


The rise in power-meter use has created huge amounts of data, with TrainingPeaks the professional package for many triathletes (two more reputable packages are Golden Cheetah and Today’s Plan), including British Triathlon’s, who upload their ride data for dissection by coaches. The results then dictate the intensity and duration of subsequent sessions. You can also compare this day-by-day, week-by-week to see if the training is having the desired effect: to race longer and faster.