Training: Why power measurement is important

By Nik Cook, Cycling Plus | Monday, January 4, 2010 4.00pm

There’s a reason all pros measure, analyse and moderate their training with power meters, and not just the heart rate monitors that we can all easily afford – they are the undisputed, most objective measure of real rider output.

According to former pro Hunter Allen, now a top coach and co-author of Training and Racing with a Power Meter, “Power is an absolute number, a direct determinant of performance velocity. Heart rate is just a response, where you don’t know if the road conditions, a dog chasing you or a mad lorry driver gave the heart rate that was logged.”

For example, a rider could go out one day and ride a 60-minute effort in his heart rate zone three with an average power output of 250W. The next week he does the ‘same’ session based on his heart rate but his average power output drops to 220W. This could be due to increased fatigue or even impending illness but the key fact is that, without power data, he’d have no knowledge of this drop in training quality or the effect his training was having on his performance.

Although power meters are expensive, it’s actually the amateur improver who is likely to get the most value out of training with them. “Your average, time-pressed rider stands to gain so much more, because using a power meter means that the few hours he has for training will be more measurable, better quality and therefore effective,” says Allen.

The immediacy and indisputable nature of the data they produce also means that power meters are great for riders who want to experiment with riding position, cadence and aerodynamics to find extra performance – without resorting to the unlikely alternatives such as windtunnels and experts to the stars.

Zoning in

As with heart rate-based training, power training is performed using a series of personalised training zones corresponding to differing levels of intensity. These zones are calculated from a ‘magic number’ known as your functional threshold power (FTP). FTP equates to lactate threshold (LT) and anaerobic threshold (AT), and is the intensity level at which lactate starts to accumulate in the body or that things begin to hurt!

Your FTP can be deduced from ride data or by more formal testing usually involving a maximal sustained effort over a period of either 20 or 60 minutes. This gives you a number that equates approximately to a 25-mile time trial effort or, in more descriptive language, horrible but bearable pain.

Training zones are worked out as a percentage of FTP. For example, at the bottom end, zone one active recovery/easy spinning would be less than 55 percent of FTP; mid-range zone three ‘tempo’ riding is 76-90 percent; and high-end 30-second to three-minute zone six efforts to raise anaerobic capacity, 121-150 percent.

By knowing your zones you can train different aspects of your physiology, identify and address potential weaknesses and accurately gauge efforts in training and racing.

Ways to measure your power

SRM: srm

1 SRM

Cost: From £875 for just the cranks, or from £1,600 for complete entry-level unit (www.srm.de)

How it works: Uses strain gauges within the crank unit

Info: SRM’s power meter systems have been around the longest and are still the ‘gold standard’ against which others are compared. The head unit is a bit bulky, but SRMs will ‘talk’ to the über bike computer Garmin Edge 705 instead. But with the entry-level model – which comes fitted to FSA’s Gossamer crankset – costing almost £1,600, you’ve got to be sure it’s right for you.

CycleOps powertap: cycleops powertap

2 CycleOps Powertap

Cost: From £539 for just the hub with wireless transmission, up to about £1,260 for hub built onto Mavic wheel, with head unit and HR strap (www.saris.com)

How it works: Uses hub-based strain gauges

Info: The wheel is as easy to swap between bikes as any rear wheel and the price is considerably lower than its SRM rival. The head unit is a bit small and can only display three lines of data at a time but the latest units also ‘talk’ to Garmin’s Edge 705.

Polar cs600x: polar cs600x

3 Polar CS600x with Power

Cost: From £418 for power sensor, speed sensor, HR monitor and head unit (www.polar.fi)

How it works: Sensor mounted on chainstay determines power from chain vibration

Info: The upside is clearly the more affordable price for the huge benefits of riding with power but the real cost is how complicated and therefore one-bike-specific the system is to fit. The head unit buttons are a bit fiddly too, and the sensors can be somewhat sensitive to knocks.

CycleOps powerbeam pro trainer: cycleops powerbeam pro trainer

CycleOps PowerBeam Pro

Cost: From £900 including HR, cadence sensors and head unit (www.saris.com)

How it works: PowerTap technology in a static trainer

Info: Using it at its simplest, just punch in the power you want to ride at (30-1000+ watts) and the extremely robust and smooth running unit constantly adjusts to hold you there.

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