In a previous article we briefly mentioned power measuring devices for cycling and alluded to a future article on what exactly power is and why it is something you should consider as training tool. I had intended to go through a big technical explanation of the physics of cycling and power, work, velocity, etc. but after I read through what I had written I thought – hmmm – got a lot of glazed over reader’s out there. There are plenty of technical articles out there already so let’s keep it simple.
What does everyone want to do when they ride their bike? GO FAST!!! It’s doesn’t get any simpler than that. However, when we ride our bikes we have all kinds of forces working against us and they SLOW US DOWN. The more forces working against us, the more POWER we need to generate to GO FAST! That’s really the best way to think of power (if you are just chomping at the bit for a more technical discussion and equations and stuff go to the end of this article for some links to just that) How can we generate more power? One way is to get stronger and push bigger gears. Other ways include pedaling faster and getting in better shape. Or, my favorite – do all of the above. Do any of these things and you will ride faster. Of course, generating lots of power is not the absolute bottom line when it comes to riding faster – aerodynamics, weight, weather, road surface and other forces that work against a rider can always be minimized (I like to think of all that stuff as FREE SPEED and you will have to wait for future article on that). For now, let’s talk about training and the EARNED SPEED which comes from increased power output.
There are many training methods and philosophies and there a many ways to measure intensity when you ride. You can simply watch that cycle computer and see your speed. Unfortunately, speed is subject to all of those pesky forces working against you and so it becomes a fairly unreliable measure of training intensity (hey, I can ride 30 mph on my rollers but it’s not all that hard) unless you are riding under very controlled conditions. You can train by your own sense of perceived exertion. Many experienced athletes train this way very effectively and will continue to laugh at the idea of doing anything but getting on the bike and riding that thing until you have to puke. (I must admit to occasionally falling into this category, myself). At the very least, I believe perceived effort should always be part of the training intensity equation. However, used exclusively and by itself, it leaves a lot of room for errors in training. I have found that most athletes, when left to their own sense of perceived effort, tend to train too hard when they should be going easy and not hard enough when they should be going hard. You can train using heart rate as your measure of intensity and I am guessing that most of you reading this article do just that. Still, heart rate training has it’s own set of limitations. Heart rate always lags behind your actual intensity. It takes a solid 3-5 minutes before heart rates reach a steady state level that matches your effort level. Because of this, heart rate is not very practical for measuring the intensity of shorter work bouts, and really the first 2-3 minutes of ANY work bout. Heart rate is also affected by many variables such as heat, hydration, stress, illness to name just a few. Like perceived effort, I do believe heart rate should be incorporated when measuring intensity. It can tell you a lot about your current state of health and fitness. Still, though, for longer steady aerobic training, I find heart rate is still my primary guide for measuring training intensity.
Power, however, is an instant, objective and direct measure of just how hard you are working. Back in ancient times you were and maybe still are asking or are being asked “what’s your heart rate?” These days you may often hear group ride banter with questions like “how many watts are you pushing?” or “what wattage can you maintain for that climb?” You ask, “aren’t watts those things that light up your house?” Yup. “Ok, so, will the rider who can light up the biggest house always be the fastest and win?” Not necessarily – remember FREE SPEED? Somewhat like heart rate, power is unique to each athlete. The more force you have to overcome the more power you need to generate. When you are really light and really aerodynamic and your bike is really clean or you take advantage of any other FREE SPEED available, you will require much less power to travel at the same speed than if you just rely on EARNED SPEED. I have been using power to earn my speed since the early 90’s when I first started using my Velodyne trainer. At first, it was really nothing more than another number to look at while I was training. Over the years, particularly when power measurement became available for riding on the road, I have found it to be extremely valuable when it comes to pacing and starting time trial, interval and hill climbing efforts. Most riders will start any training or racing effort much too “fast” or “hard” without realizing it – they see heart rate low, their perceived effort isn’t very high – yet – so they push, but their power output, if they were measuring it, will typically be much higher than they can maintain for the entire length of that effort. Ultimately, they end up having to slow down to reduce their heart rate and lactate production. I believe that any training at levels higher than basic aerobic endurance training is going to be more effective when using power as the primary guide ro measuring intensity.
There are currently three reliable and relatively accurate systems available to measure power output while riding your own bike on the road or trail – The SRM, the Power-Tap and the Polar S-720i. They all have advantages and disadvantages associated with them and to go over all of that and try to determine which is the “best” has more or less already been done (see http://mywebpage.netscape.com/rechung/wattage/ ) The SRM is generally regarding as the most accurate and most direct measure but also the most expensive. The Power-Tap is nearly as accurate although not quite as “direct” since power is measured at the hub/wheel rather than the crank/bottom bracket (I kind of think this provides a more useful measure, myself, although you will be giving up a few watts to brag about). It sells for a quite a bit less than the SRM. The Polar S-720i, at first glance, seems like it would not be very accurate, but it actually does a pretty good job and it’s only real drawback is the actual set up and calibration process which I know is enough to scare away a number of potential buyers, regardless of the price. A complete system will cost you about the same as the Standard Power-Tap and a bit less than the Power-Tap Pro. I have used the Standard Power-Tap since it first came out and currently use the Power-Tap Pro which has been updated and improved by Saris/CycleOps. I love it and recommend it. I’ll even sell you one if you are interested ;-)
Finally, you ask, “ok, if I go out and buy a power meter for my bike, how do I use it in training?”. If you are familiar with heart rate training zones it won’t be a difficult transition to understanding power training zones. In both cases, the zones are based an athlete’s output or intensity at their lactate threshold. One way to determine lactate threshold is to go visit Doc Dan and undergo a lactate test in the lab. Another way, that may be more convenient but definitely more painful is to perform a 20-30 mile time trial or make an attempt at your own hour record. The power/heart rate/lactate that a cyclist can maintain for ~60 minutes is very very close to the lactate threshold determined by a laboratory test. If you are not in shape for that kind of ride or simply don’t have the stomach for such an effort, I would recommend the lab test. You can always do a shorter distance – maybe 8-12 miles and consider 93-95% of that power to be close enough to your actual threshold. Once you have your number – let’s use 300 Watts as our example – you can determine your other training zones.
AEROBIC (30-360 minutes)
A1 = <75% or <225 Watts (Recovery and Easy rides)
A2 = 75%-85% or 225-255 Watts (Aerobic, Endurance, Long rides)
A3 = 85%-90% or 255-270 Watts (Aerobic Threshold, Tempo, Long races)
LACTATE THRESHOLD OR AEROBIC POWER (20-150 minutes)
AT1 = 92%-95% or 275-285 Watts (Tempo, Longer time trials, sub-threshold training)
AT2 = 95%-98% or 285-295 Watts (threshold training, road races)
AT3 = 98%-103% or 295-310 Watts (time trials, threshold training, long climbs)
VO2 MAX or AEROBIC CAPACITY (3-10 minutes)
VO2 = 103%-125% or 300-375 Watts (shorter time trials, pursuits, VO2 max intervals)
LACTATE TOLERANCE or ANAEROBIC POWER (30-150 seconds)
VLa = 120%+ or >360 Watts
MAX POWER or ANAEROBIC CAPACITY (5-30 seconds)
VLa MAX = all out
For more technical discussions of power and related information try
http://www.analyticcycling.com/
