Power Power is the rate at which energy is used (energy over time) and is measured in watts. In cycling, energy is expressed in terms of work (such as how hard you have to work to ascend a climb). It’s a constant snapshot of your work rate at any given moment. It’s the building block from which all power-based training flows. One cool fact: A watt is a watt, whether on a bike or powering your home. So when Lotto-Belisol’s Andre Greipel unleashes 1,900 watts in a sprint, he could essentially power two houses at normal consumption level. Another comparison: 1 horsepower is 746 watts. Average Power Average power probably won’t be on your home screen, but it might be in the second or third menu. This is exactly what it seems: your average power output over the whole ride, just like your average speed readout. Here’s the key: It includes coasting, so as we’ll see in a moment it’s only a part of how hard you rode (see Normalized Power). A Tour de France rider will average 200-300 watts for a four-hour stage; that’s an intensity most recreational riders can sustain for only an hour or so. KiloJoules The basic unit of work, the kJ has a happy confluence in that for most rides one kJ becomes roughly equal to a kilocalorie (or what nutritionists just call a calorie). The actual rate is 4.18kJs = 1 calorie, but people range from 20-25 percent efficiency. So for every, say, 100 calories burned in exercise, only 20 to 25 propel you forward and are measured at the power meter. The rest is turned into heat. If you know your power output and time, you can calculate kJs, or calories burned. If you’re trying to lose weight, kJs are the single biggest thing you can focus on. Our bodies burn a different ratio of fat to carbs at different exercise intensities, so it’s not entirely straightforward. But, very simply, if you go for a two-hour tempo ride and burn 800 calories, but consume two 20-ounce bottles of hydration mix (250 calories each), and a 200-calorie energy bar, you’re not going to lose weight. A power meter keeps you honest about how much work you actually did and how much fuel you actually need to power that workout. For reference, Tour riders will typically produce upward of 3,000 kJs of work on a stage. Threshold Power This is a vital measurement of how much power you can sustainably produce over a one-hour period and is a fundamental metric of fitness. It’s often expressed in watts produced per kilogram of body weight (see w/Kg). Want to test your own? The protocol is a 20 minute all-out time trial, typically on a steady climb. But pros often do a specific series of tests that ensures better accuracy. After a 45-minute warmup, do maximal efforts in this order, with full recovery (5-10 minutes very easy pedaling) in between each effort: five seconds (peak neuromuscular power); five minutes (peak aerobic power); 20 minutes (threshold power); and one minute (peak anaerobic capacity). Your functional threshold power is 95 percent of your 20-minute power number. Neal Henderson, coach to Taylor Phinney and Evelyn Stevens, says that the threshold test must be preceded by the peak aerobic power test, or it will skew high. Normalized Power Since power meters record zero power during coasting, that’s factored into your average power output over the duration of a ride. Normalized power strips out the coasting sections, so you get an accurate average power number for only the portion of your ride you were pedaling. It will always be higher than average power. Average power is still important, however; compared with normalized power and ride duration, you can get a sense for how intense the ride was. Watts/Kg Raw watts aren’t the most reliable metric of performance, because riders put out varying levels. A big rider like Argos-Shimano’s Marcel Kittel can generally produce higher watts on flat or rolling terrain than a climber like Nairo Quintana of Movistar, but since Kittel is larger he must produce bigger numbers to keep the same speed. A better measure, especially on climbs, is watts produced per kilogram of body weight (that normalizes the size difference). This is commonly used when talking about threshold power, but it factors for the other tests as well. How much better are Tour riders than the rest of us? A contender for the overall classification can produce just above 6 w/Kg on major climbs of the race. By comparison, a domestic pro could manage a best of 5-5.5w/Kg; a good, competitive amateur or masters’ racer can put out around 4w/Kg and an untrained person would struggle to produce 2.5w/Kg. That’s right, a Tour pro can produce about 50 percent more watts than a competitive amateur racer and more than twice what an untrained person could. Training Stress Score TrainingPeaks developed this metric, called Training Stress Score (TSS), which measures the relative intensity of a ride, by measuring how much of your threshold power you produced and for how long. It’s relative to the rider by fitness, not size, so two equal-size riders could get a different score for the same ride if their fitness varies. An all-out one-hour effort gets a TSS of 100. Two hours, hard, is 150 and a century is about 225. A typical Tour stage can be anywhere from 250 to 400. TSS is valuable for determining when you’ve gone extremely deep and need to recover, and TrainingPeaks feels that for training, it’s a more exact metric than kiloJoules of workload for a particular rider. Heart Rate Just because power is more exact a measurement of training doesn’t mean you give up on heart rate (HR). It still matters because this is your body’s response to the work. And it’s an important barometer of how you feel. Let’s say you go ride and on a climb you feel awful; your heart rate spikes but your power just isn’t there. You might be overtrained, or getting sick. An unusually high HR signals that something’s not right; you won’t get much out of training today so you should head home and let your body rest. Cadence Power is work over time, right? So there are two ways to increase your power: You can boost the actual force on the pedal, or you can increase the number of times the pedal goes around in a minute. That is cadence. You’ll notice if you ride with a power meter that when you downshift and pedal a higher cadence, it might feel a little easier at first, but your power actually increases. Even though you’re not putting the same amount of force into each pedal stroke, the increase in cadence means there are more pedal strokes per minute. So, more total power.
Posted on: Wed, 19 Mar 2014 11:32:15 +0000
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