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Why Do I Need a Power Meter?
Written by Dr. SkibaExercise professionals have always wanted to be able to track athlete training accurately, and with good reason: Athletes exhibit different, specific responses to different types and amounts of training. However, you encounter problems when you try to describe training. For instance, if I asked you how much cycling you do, how would you respond? It is a more difficult question than it might appear. If you responded by saying, “I put in about 100 miles a week,” you really didn’t tell me anything. You rode 100 miles, but you didn’t say how fast you went. 100 miles at race pace is a lot harder than 100 miles of easy spinning with your mates.
Instead, you might say, “I put in about 100 miles at about 17 mph.” Yet, even this statement does not tell the whole story. Is 17 mph fast for you? What percentage of your race pace does that translate into? Moreover, you really didn’t just train at 17 mph, did you? You did a variety of different rides. These details make important differences not only in communication, but also in your development as an athlete and your body’s response to the training you do.
Most triathletes answer this challenge by relying on heart rate based training methodologies. They divide their training into zones (e.g. percentages of maximum HR), and then say things like, “I did 2 x 30 minute intervals on the bike in zone 3.” Now we are headed in the right direction: We know how long the athlete trained, and we know how hard the athlete trained. Or, do we?
I’m going to break some bad news to you. Your heart rate monitor is not a good measure of training stress. The problem is that what it measures (your heart rate) is variable based not only on the exercise you are doing, but a lot of other stuff that has very little to do with the training task at hand. For instance, heat stress will make your heart rate higher at the same work rate. Overtraining may make it lower. Excitement will make it higher. Dehydration will make it higher. Lack of sleep plays a role. You get the idea here. Heart rate is just plain too unreliable. It’s what we call a dependent variable: your heart rate is dependent upon all those things, and on how hard you train. You might think you are in zone 3, but you might be in zone 2 or 4.
What you need is something that tells how much work you are doing directly. Enter the power meter, which mechanically measures your work rate. Power output is always an accurate reflection of your workout…your 5-minute maximal power is your 5-minute maximal power, no matter how your heart responds to your attempt at generating it. Now we have an objective measurement of exercise intensity, and can both manage training and communicate about that training in terms everyone will understand. For instance, it doesn’t matter that my 5-minute power is 500 watts, and yours is 600…the point is that when either of us says that, we both understand what we mean and how intense that is. More importantly, training at that level will result in similar adaptations for the both of us…it will increase our VO2max, or our power output at VO2max, or both (among other things). See how easy that was?
An additional benefit of working with power is that you can use it to quantitatively track your training load over time. Dr. Eric Banister first foisted this concept in the 1970’s. Called the Training Impulse Score (TRIMPS), it relies on HR data, which means it is sensitive to all those bugaboos we mentioned before. However, Dr. Andy Coggan solved this problem in the early part of this century with his Training Stress Score (TSSTM), which relies on power data. You can now generate a numerical value that compares any given workout to a known stress (e.g. your 1 hour power, which is highly correlated with LT and your overall ability as a triathlete). This allows you to learn precisely what quantity of training over a period of time is necessary to get a particular result. In fact, you can actually use this kind of data to mathematically predict your exact performance on race day using some proprietary software I have developed. You can check my website for a few details.
Your next question should be, “Can this be done for running?” The answer is yes. In 2005, I developed a system known as GOVSS(TM), which allows the calculation of power output for running athletes, as well as the generation of numerical values to quantify the training stress incurred by the athlete. If you have a GPS, you can use GOVSS, and all the information is available free on my website. It will change the way you look at your training.
At the end of the day, the take home message is that power data is powerful data. If it is within your means, I highly recommend taking your training to the next level using power data.
