Power meters: Everything you need to know
Power meters: everything you need to know
Check out what Power meters are available to you>>>
Let's face it, cycling's a great sport for gadget lovers. Heart-rate monitors, GPS, smartphone training apps and power meters are all there for the taking. But among them power stands out as the ‘future' best friend for any cyclist that wishes to train to their full potential.
As such, power, or more specifically the mighty ‘watt' has become common currency for riding and training discussions among the growing percentage of cyclists who have invested their ‘hard-earned' in a power measuring device.
The knock-on effect is strong, and aspirational riders, listening with intent, seek to get on the bandwagon, such that now power meters are a booming market.
However, do we actually understand fully how the magical wattage figures displayed on the screens of our various bicycle computers are generated and what they're telling us? In many cases we suspect not, and what's more even with an understanding of what is being measured, using that information beneficially is a different ball game again.
As we progress through this feature, we'll summarise what products are currently available, touch on the relative pros and cons of the various systems, talk to industry experts, leading coaches, pro riders past and present, and challenge some myths and misconceptions.
Although power has only hit the mainstream in recent years, the first commercially available portable power meters, the SRM (Schoberer Rad Messtechnik) system designed by German Ulrich Schoberer, appeared over two decades ago, in the late Eighties. Cost was a big factor in the early years, making the SRM system prohibitively expensive to most, and kept it penned within physiological test labs and the pro racing ranks for a long while.
Since those early days, as with other electronica such as computers and mobile phones, technology has made the seemingly impossible viable, and costs have fallen considerably.
The science bit - What is power?
That about wraps up what products are out there, but to explain what the data is actually representing we needed to get scientific. For that we needed expert help, and a man in a lab coat - enter Professor Louis Passfield (pictured).
Not just any old prof, Passfield is currently based at the University of Kent Centre for Sports Studies, and has a vast wealth of experience in this precise field.
He was the first scientist to work and study with SRM power meters in the UK, which included his involvement in the preparation for Boardman's successful attempt on both the Barcelona Olympics and the Hour record. He's also a man world renowned for his work with pro riders and national squads, so with credentials like that, who better to ask?
Here's what we gleaned... in distilled form
The maths: power (W) = force x distance / time
Watts are the energy required to a move a mass a certain distance in a known time period. 1W = 1Nm/s in other words to move one Newton one metre in one second costs one watt of energy.
So in bike speak, the mass is you plus your bike, and the distance is the ground covered, but moving a bike is a far more complicated scenario, as its resistance to motion is far from consistent, hence the measurement of power is not taken quite so literally as the raw equation implies.
Given that power = force x distance (or displacement) / time
And, displacement / time = velocity
A simplified equation is:
power = force x velocity
And that is the key to understanding how a power meter works. It's essentially applying that equation to a given part of the bike - be that BB axle, crank, hub, pedal axle etc.
whereby, the speed of the movement, or angular velocity is measured and multiplied by the size of the force - force having been calculated by strain gauges. With those figures in hand the energy cost is therefore quantifiable as power (watts).
Accurate measurement of this force is one of the biggest challenges power meter manufacturers face. The microscopic bending measured by the strain gauge is the key to accurate results, so the smallest details become important for instance the placement of the gauges, the quality of the gauges themselves and even the temperature of the measured material. This may help to explain why the best systems are not cheap.
What is a strain gauge?
So, we know that power meters use strain gauges, but what exactly are they?
In short, a strain gauge is a component within a balanced electrical circuit ie resistance is known and constant. As a force (or strain) is applied, two things happen - the strain gauge shape deforms and subsequently its electrical resistance alters, plus there is a piezoelectric effect (a voltage generated by pressing on or squashing electrons).
These two reactions to the applied force upset the balance of the circuit and it is this difference and the resultant electromagnetic force that is effectively being measured and converted into a quantifiable measurement of force.
Power: the game changer
Power changed training fact. Monitoring your speed can tell you only so much about a ride, heart-rate monitors can tell you a bit more, but knowing your power output is a quantitative, repeatable way to assess how hard you are actually working. As Professor Passfield perspicaciously puts it, "enabling another layer of the onion to be peeled back in the scientific conundrum of analysing performance".
From a coaching perspective, the flip side is that with power data you can also accurately determine the specific performance requirements of a given event/discipline. That's almost like being given the answers to the exam questions, except of course the athlete still has to put the work in to reach the targets. But just having that predictor is hugely beneficial.
Professor Passfield stresses there is still much to be learnt, and we are, in his opinion, still a way off knowing enough to be overly prescriptive with training techniques. But, he says, "a power meter provides us with a far better understanding of different events so you can be incredibly precise in working out what needs to be replicated in training".
Passfield goes on to say: "Having access to power is one thing - but having numbers alone isn't going to make you a better bike rider - it only adds value if you are able to use the data. Heart rate data still has its place and it's important to use that alongside wattage. Riding to a specific power alone will tell you what work you are doing but not at what physiological cost."
For example, one use for mapping power and heart rate simultaneously is to indicate whether the pace you're riding is sustainable. A constant power but rapidly increasing heart rate means it's highly likely that you will soon blow. A decreasing heart rate could mean there is scope to press on and up the power output.
Power meters give you the scope to gather data for the same ride over a period of time. It's this aspect that Passfield believes is their biggest advantage, allowing you to be more objective with your training. In other words - you might well have got a slower time over a given training route, but if your power numbers are up, for a lower physiological cost (reduced heart rate) then it's pretty conclusive - your training is working!
Power can also tell you when it's time to rest. Seeing either significantly lower power outputs for a known heart rate, or higher heart rate for a known power means it's probably time to cut a ride short and head for home.
Heart rate data still has its place, and it's important to use alongside wattage. Riding to a specific power alone will tell you what work you are doing but not at what physiological cost.
Chris Boardman interview - Boardman: power in perspective
A household name in UK cycling and a man synonymous with a meticulously calculated approach to training, especially in the lead-up to his successful Hour record attempt, working with coach Peter Keen, Chris Boardman takes us through his thoughts on power and training.
"Power meters are superb tools, but you need to be able to use the data. Before you use any measuring device, you need to define exactly what you want to achieve.
It's a bit like using scales in loosing weight - it's a tool to help you achieve your goal. "The most important thing to remember when measuring performance is the three Ps - Power, Perception and Pulse. Numbers don't tell you how you feel. I never raced to data - either the hour record or at a prologue.
I removed the data from sight and once the effort was completed I would then look at the numbers. I simply used the information retrospectively to back up my own perception of effort.
"People forget about perception. British Cycling coaching style changes with every athlete it coaches. You have to be careful not to over-focus on the data. Power is a big part of [modern] coaching, but the rider needs think about perception.
It's the intangible stuff, but it's what controls the ride. Power data needs to be used by more than one person to allow it to be used in perspective - it needs a levelling voice such as a coach. Power needs to be used in partnership.
"Power can be dangerous to a super motivated person, using it without the levelling voice can mean athletes struggle to take time off. Ninety per cent of athletes who should have performed better in a race did too much training - recovery is where you improve. Power meters can help training, but need to be used with the three Ps!"
What can a power meter do for you?
Power meters are an invaluable tool in facilitating reliable, quantitative analysis of training loads and efforts, but they are not for everyone. If you're still left scratching your head and undecided about whether to make the leap and invest, then maybe the following balanced argument will help.
If nothing else it will at least make sure you aware of the bigger picture before you get started.
- Eliminates guesswork from gauging exercise intensity, so training becomes less haphazard.
- Quantitative tracking of fitness levels over time (when combined with other physiological data - heart rate etc) that provides conclusive evidence of training adaptations, including overtraining.
- Help to define your weaknesses.
- Monitor your effort levels (pacing) during an event.
- Train more specifically for the demands of your chosen event(s).
- Aerodynamic position testing.
Best suited to a rider who is interested in analysis and number crunching, otherwise it tends to end up as ‘just another thing to do'. That's an expensive lesson to learn.
It's not an instant gratification product. Just owning a power meter does not make you an overnight pro. It takes patience, learning and dedicated training to reap the rewards.
Self-diagnosis is not a sensible or recommended path to follow. Interpretation of data requires knowledge and experience, either yourself, or with the help of a coach. The idea of having a power meter was to remove the guesswork - remember?
You can easily get bogged down by numbers. Don't forget the fundamentals of why you ride a bike - to enjoy it. Beware of the ‘paralysis by analysis' syndrome where you are a slave to the numbers. Trust us, you'll quickly start to lose your ride buddies if you do.
Power meters are highly sensitive electronic devices that need to be treated with some care to maintain accuracy and functionality. They are not fit-and-forget items. Expect some upkeep and servicing costs, which might range from simple battery replacements to more skilled procedures carried out by service centres.
Five things we recommend before you start.
1) We can't stress this enough... Have a clear idea about how you intend to use a power meter in order to get the most out of owning one. Bragging rights in the cafe or just getting one because your mates have all got them is likely to be a big waste of your money.
2) Get a fitness test so you can be conclusive about what your starting point is and also provide clear goals/targets to re-evaluate.
3) Understand training zones and the need for rides to be more specific and outcome-dependant. Be aware this may mean some rethinking of your daily rides or habitual old routes.
4) Consider a coach and following a set training plan to ensure your power meter is going to provide the best return for your investment with an upward spiralling of your wattage figures.
5) Be clear about the bike, or indeed the possibility of multiple bikes that you would like to use the power meter on. This will help steer your purchasing decision, and potentially cut down your options.
Trouble deciding to make the leap? Why not rent a power meter? It's a good way to make 100 per cent certain it's for you before you take the plunge. Searching online is your best bet. Cyclepowermeters.com is well established in the UK, and offers all the latest designs and configurations on monthly rental plans.
Another idea might be to split the cost with a friend, and share the use of a power meter, on a weekly or monthly basis. Food for thought at least?
Check out what Power meters are available to you>>>
This article was first published in the April 26 issue of Cycling Weekly. You can also read our magazines on Zinio and download from the Apple store.