The Power Game:
You are on your bike in the middle of a two hour ride and do to the headwind, you are going a tortoise like 20km per hour. Although this might demoralize you mentally, physically, you might be getting just as good of a workout as if you were going 35km per hour with no wind. As prices decline, more and more triathletes are using powermeters (wattage) to be more specific with their training protocol. The advent of portable powermeters such as Power-Tap and SRM, alongside with the indoor CompuTrainer, has allowed athletes to measure their power more competently.
Before powermeters or heart rate monitors, athletes gauged intensity by their rate of perceived exertion (RPE). Triathletes may describe their workouts as hard, moderate or easy. These terms generalize to others the intensity experienced during a workout. Many athletes are so in tune with their body that they can pretty well gauge intensity; however, RPE is still subjective. Then along came handlebar mounted computers that could measure speed. However, speed is influenced by factors such as wind and hills.
The accessibility of mobile heart rate monitors allowed athletes to assess intensity and create training zones to help determine the intensity of workouts depending on the athlete's goals and their periodization of training. Heart rate training also had limits as heart rate could be affected by stress of the athlete, air temperature, humidity and diet. These conditions distort the relationship between heart rate and RPE when compared with velocity. For example, a ride on a hot day will affect the mind and body differently than on a cool day. Another limitation of heart rate based training is the time lag that occurs between a change in intensity and the resulting shift in heart rate. For example, at the start of an interval, heart rate may take several seconds or even minutes, to catch up with the RPE.
Power
Power provides a direct measure of the rate of work produced by a cyclist. If a greater amount of distance is done in the same amount of time, more power is required. In cycling, power is determined by pedal force multiplied by leg speed. As force applied to the pedals goes up with constant pedal speed (or cadence), then power goes up. Conversely, if cadence goes up with constant pedal force, power also increases.
Power, measured in watts, is an excellent gauge of training intensity. There are no subjective rating problems as with RPE. Hills and wind don't confuse watts as happens with velocity. In contrast with heart rate, wattage is immediate with no delay in information.
Critical Power Zones
The best way to use power in training, like heart rate, is to determine zones. In coaching, I use five heart rate zones based from an athlete's lactate threshold. For power training, I construct zones based on Critical Power (CP) or average power.
Have you ever raced in a time trial and crossed the finish line flogged, as if another mile was not possible? If you used a powermeter, it would have been possible to determine the CP for the duration of the race. For example, say the time trial distance was 40 km and your time was 60 minutes with an average power of 260 watts. You could then say that for 60 minutes, you are capable of averaging 260 watts. But if the race time was doubled to two hours, would you still be able to average 260 watts? No, because at that power output you would be exhausted at 60 minutes and unable to continue. What if the duration was shortened to 30 minutes, would a higher average power be possible? Yes, as there would be energy still in reserve at 30 minutes.
For any given duration you have a CP. By consistently training at or near that CP, your ability to perform at that workload improves. For example, lactate threshold fitness improves when training near one's lactate threshold, which is the power output that can generally be maintained for about 60 minutes by a fit rider. By knowing the CP for 60 minutes, it is possible to train very precisely using the physiological systems that limit lactate threshold. Although you would not often want to train for 60 minutes at your CP/lactate threshold, breaking workouts up into intervals will enhance your training. Such a workout might be 3 intervals of 20 minutes duration each with 5 minute recoveries. The intensity of the work intervals would be the CP for 60 minutes plus and minus 5%, thus establishing a training zone. Let's call this zone CP60. If the 60 minute average power is found to be 260 watts, CP60 is 247 to 273 watts. Likewise, CP zones can be determined for other durations that are conceivably related to various physiological fitness adaptations.
Suggested CP zones for triathletes are 6 minutes (CP6), 12 minutes (CP12), 30 minutes (CP30), 60 minutes (CP60), 90 minutes (CP90), and 180 minutes (CP180). Each of these CPs can be determined by simply carrying out a time trial at a prescribed duration using a powermeter and then computing a zone by adding and subtracting 5% of the average power. Testing at the longer durations is difficult to determine in training, but it appears these zones can be predicted by graphing and projecting from the shorter CPs of CP12 through CP60.
Testing Critical Power
Testing should be done at the end of a recovery week and the athlete needs to test with as even as possible intensity throughout the CP test period. For instance, for a CP30 test you don't want to go extremely hard at the beginning, only to fade midway through the 30 minutes. The average wattage will not be a good indication of what you can maintain consistently throughout that period. After a few trial and errors, you will be more consistent with your intensity. Ideally, a test of the same duration should be done every 4 weeks.
Training with Critical Power
The way in which you use CP to train depends on your "A" priority triathlon race distance. Keeping in mind that a triathlete has to run off of the bike, an Ironman distance triathlete with a good base should be able to do a 6 hour ride at 65-70% of CP30. An athlete competing a half Ironman distance race should be 75-83% of CP 30 and an Olympic distance athlete should be 83-90% of CP30.
Some Examples of CP Workouts Pertinent to Triathletes are (after a warm up):
Aerobic development. Ride a flat to gently rolling course with grades slight enough so that you primarily stay in CP180.
Hilly endurance ride. Select a course that includes moderately steep hills of up to 6% grade that take several minutes to climb. Maintain cadence at 60 rpm or higher while in CP6 to CP30 on the climbs.
Big gear climbs. Find a hill with a moderate, 4-6% grade that takes 1-3 minutes to climb. Select a gear that lowers cadence, but not below 50 rpm, and maintain CP6. Recovery is 2-3 minutes. Progressively build up to 30 minutes of accumulated climbing time in one workout.
Tempo. On a mostly flat course, ride at CP90 for an extended time without recovery. Start with 20-30 minutes of tempo and build to 45-60 minutes by adding 5-10 minutes each week.
Criss-cross threshold. On a mostly flat course, ride 20 to 40 minutes alternating between CP90 and CP30 every two minutes.
Anaerobic Endurance intervals. On a mostly flat course, do 4-6 intervals of 3-5 minutes duration. The cadence is higher than the anaerobic portions of your event. Power is CP6. Recover at less than half of CP12 for the same time as the preceding work interval.
Hill Intervals. Go to a 6-8% hill that takes 3-4 minutes to go up and do 4-8 climbs with a relatively high cadence. Power is CP6. Recovery is 3-4 minutes, depending on the duration of the climb.
Nearly all of the above workouts can be done on an indoor trainer. Indoor training has some advantages over road training such as no cars, stoplights or dogs. Also, hills and changes in wind direction are non-existent.
When to Stop
When an athlete is tired, it shows in their power numbers. A lower than usual power to heart rate ratio or a higher perceived effort for a given level of power are indicators that an athlete should rest. Whenever your average power fails to achieve a CP zone, or a reasonable power goal is not attained, it's time to stop the intense portion of the session.
Although training and racing will never be an exact science, using power takes out much of the guesswork. Depending on the distance of your "A" priority race, training at race power output gives you an edge over your competition.
Wes Hobson - www.weshobsonperformance.com
* References - Joe Friel - www.ultrafit.com
