by Fred Matheny
This concept in a nutshell: The development of reliable and lower-priced power meters over the last decade allows us to measure and use training intensity in a whole new way.
For most of cycling’s history, riders determined their intensity by feel. They went “easy” or “ hard” or simply noted their gearing. A long aerobic ride was done in a 42×17-tooth gear and intervals were hammered out in 53×15. Although these were only approximations of intensity, they worked for generations of riders.
With the development of accurate heart rate monitoring in the mid 1980s, training entered the scientific age. Cyclists began downloading their workout heart rates into computers for analysis. Heart monitoring became a staple of aerobic exercise machines and cardiac rehab programs as well as a must for serious athletes.
The newest method of gauging intensity is power measurement. Several products allow cyclists to put a number (watts) on power output using strain gauges on their bikes. There are wheel based, crank based and even pedal based power meters from a variety of manufacturers.
Let’s look at why anyone would plunk down enough money to buy another bike just to know wattage output.
What’s a Watt?
Because intensity is the best producer of fitness, measuring intensity is the key to efficient training. But why not simply gauge it by speed or by how hard it feels like you’re working or by heart rate? Three key reasons:
• The intensity needed to produce a certain speed varies depending on the wind, pavement quality and whether the road tilts up or down.
• Measures of perceived exertion can be accurate but require practice and careful monitoring of how you feel.
• Factors such as hydration status, air temperature and fatigue can cause heart rate to vary widely at a given power output.
Power monitoring, on the other hand, is accurate simply because a watt is always a watt regardless of outside factors.
According to Dr. Allen Lim, a sports physiologist, power training expert, and founder of Skratch Labs, “Power training provides a direct and objective measurement. It’s like giving a chef a thermometer. You can bake a pie without knowing how hot the oven is, but it takes a lot more attention and experience. Having a direct way to monitor the process (training or cooking) allows athletes to understand their training and race environment. You don’t end up burning as many pies before you figure out the perfect recipe.”
In fact, some coaches would argue that power monitoring is the Holy Grail of training because it tells you exactly how hard you’re working, day after day. It’s objective and foolproof, the sort of hard data that can transform training from art to science.
According to SRM inventor Ulrich Schoberer, “The basic element of riding faster is to increase power output rather than heart rate or lactate. It is simply power. All other values are the second choice.”
Even more important, exercise scientists can use power meters in races to pinpoint the demands of competition. How many watts did the winner of Paris-Roubaix generate on the cobbles of the Forest of Arenburg? How many times during the race did he have to achieve that wattage figure? How many watts did Geraint Thomas average when he was climbing l’Alpe d’Huez?
By knowing these figures, riders and coaches can set up training programs that duplicate the demands of racing. Recreational riders can use a power meter in centuries or local time trials to do the same thing.
As Lim says, “We can finally see what athletes are doing in races and begin to manipulate their training so it’s more specific.”
Apply Wattage Information to Your Riding
Simply knowing how many watts you average as you blast up your local killer hill isn’t enough. That number is simply a number unless you know what to do with it. According to Joe Friel, a Colorado endurance sports coach and author of The Cyclist’s Training Bible, a good place to start is by determining your average power or “critical power” (CP) for various time periods. (Learn more: What’s a good average wattage for a cyclist?)
Friel recommends determining CP for 12 seconds, 1 minute, 6 minutes, 30 minutes, 1 hour and 3 hours. Then you can determine exact training loads for interval workouts.
One way to visualize this is by comparing it to weight training. Let’s say that a strength athlete can bench press 400 pounds one time with a maximum effort. So, 400 pounds is his one-rep max (abbreviated 1RM.) Once this has been determined, he can work out at a specific per- centage of his 1RM, doing (for example) 5 sets of 8 repetitions at 80 percent of 1RM, or 320 pounds.
Similarly, once you know your CP for, say, 6 minutes, you can do intervals at a given percentage of that figure. If your CP for an all-out 6-minute effort is 400 watts, you might do 3-minute repeats at 80 percent (320 watts). As you get stronger, you can increase the wattage and the duration of the intervals.
Power measuring means that the intensity of workouts can be precisely controlled.
Measuring Power and the Race of Truth
Power measuring is also great for time trials or non-drafting triathlons where it’s just you against the clock (and the wind and the hills). These events require you to accurately dole out energy for the whole distance so you go as fast as possible and finish spent. Go too hard early and you’ll slow abruptly before the finish and lose time. Start too slow and you’ll finish with energy to spare, well above the best time you could have recorded.
Experienced time trialists apportion energy by feel. They sense exactly how hard they can ride to finish the race exhausted, their last dollop of energy burned in the final 200 meters. However, such knowledge of the body takes lots of time trialing.
Power metering makes success more objective. If you know the average power output you can sustain for the duration of the event, you can simply maintain that level, secure in the knowledge that it’s your optimum pace. This works much better than trying to ride at a certain heart rate because of a phenomenon known as “cardiac drift.” Heart rate tends to rise as an event wears on, even though wattage stays constant.
Of course, time trialing isn’t a steady-state effort unless the course is dead flat with no wind. Even then, you’ll go harder when accelerating at the start and turnaround. On most courses, you have to go slightly over your limit on hills and out of turns, then recover a bit on easier sections.
Many riders use a heart monitor to gauge their intensity in these conditions. But because heart rate lags behind effort, by the time you know you’re going too hard on a hill, it’s too late. According to SRM’s Schoberer, “With heart rate, there’s a delay in the response to effort, sometimes as much as two minutes. But with power, you can control your effort precisely.”
A power meter shows you immediately whether you’re below, at or above the wattage that your experience says you can maintain.
Comparing Wattage and Heart Rate
Of course, knowing your heart rate is still important. One advantage of power measuring is the ability to see wattage and heart rate simultaneously. Even though heart rate is influenced by the environment and other factors, it’s still a useful measure of what’s going on in your body.
If you know the heart rate usually associated with a given wattage and duration, you can watch for variations and realize when you shouldn’t be training hard. For instance, suppose you normally see a heart rate of about 170 while doing 3-minute repeats at 300 watts. Today, however, you’re struggling to put out 250 watts at 170 bpm. That’s a clear sign you’re not fully recovered from previous training. Cancel the interval session and spin slowly home feeling smart, not guilty. Make sure you’re rested, well hydrated and your muscle glycogen stores are replenished with high-carbohydrate foods before you try again.
Importance of Perceived Exertion
Nor does power monitoring mean that perceived exertion is passé. In fact, according to Dr. Lim, many pro riders who use power meters have done away with heart monitors. They prefer to check wattage and compare it to their subjective feelings of intensity. This is how Jonathan Vaughters, a big proponent of power measuring, does it.
Says Lim, “Make sure you listen to your intuition when you use a power meter. One of the major benefits is developing a better sense of feel when training and racing.”
Once you’ve “calibrated” your feelings of intensity to the objective measures made possible by a watts meter, you won’t need to refer to the handlebar-mounted electronics as frequently.
Knowing wattage keeps you in line when going easy, too. Because intense training is so demanding, you need plenty of easy spinning to promote recovery. But despite the best intentions, it’s common for effort to creep up during easy rides until the pace is too hard to allow recovery. Seeing the number of watts you’re putting out prevents you from overriding perceived exertion and gradually increasing the effort. It also helps you avoid getting sucked along by a group that’s too fast for the day’s goals.
Personalizing Your Training with Power Monitoring
You’re a unique bike rider with your own physical attributes and liabilities. No one else can decide how you should train. Power monitoring is a powerful tool to help you learn about yourself.
Lim’s advice: “Employ the scientific method to answer personal questions about training.” These, he says, are the crucial ones:
- Do you produce more power at a higher or lower cadence when climbing?
- How do different pacing strategies in a time trial affect performance?
- What is the relationship between total work done and time spent in varying intensity zones?
- How does time in different intensity zones affect feelings of perceived effort, fatigue and performance?
- What are the specific power demands of key events, and how does competitive power output compare to your power output in training?
With a power meter, you can answer all of these questions, then tailor your training to your own goals and talents.
Training with Power is an Efficient Use of Time
Power monitors are useful for time-challenged riders. If you have only one hour to train on a given day, it’s important to use every minute to best advantage. A power meter makes it possible by telling you exactly how hard to work. No more inefficient guessing.
And a power meter is simply unbeatable for progressively increasing the workload over several weeks or months. I’ve talked with a number of riders who began using one and saw significant gains. They had reached a high level of power production in previous seasons but had plateaued.
In addition, a power meter converts any standard indoor trainer into a ergometer. Simply mount your bike and do a precise wattage workout at any time of day (or night) despite outside conditions.
If you have a smart trainer, it will measure power directly and doesn’t require a separate power meter. Smart trainers also allow you to load workouts based on your current abilities that will force you to pedal the exact prescribed wattage for each of your intervals for the entire interval when you use the ERG mode. No more starting out too hard, or slacking off at the end!
The Downside of Using a Power Meter
Despite all of these advantages, power monitoring isn’t right for everyone. I won’t fault you if any of these drawbacks are significant enough to stop you from getting into this new technology.
• Cost. An accurate power meter costs several hundred dollars.
• Complexity. Experienced riders may be content with simple perceived exertion as a gauge. With experience, it can be nearly as precise as a power meter for most training purposes, and it costs nothing.
• Pressure. Some riders object to yet another number that goads them into going at a certain pace. These riders may have tried heart monitoring and decided that they didn’t like the constant judgment of their effort.
• Clutter. Some riders hate attaching more equipment to their bikes.
• Information overkill. Many recreational riders may not care about fine-tuned performance. For them, power metering is a waste of time and money.