Question: Should I train and race with a heart rate monitor or a power meter? What are the pros and cons?
For mountain bike training, I recommend using a power meter, perceived exertion and a heart rate monitor. The more data you have, the more tools you have at your disposal to measure performance and improve your training.
The Bottom Line
Use a power meter extensively in training to best mimic racing demands, track measured changes in fitness, nail training objectives, and effectively calibrate perceived exertion with reality. Changes in power output give you a direct, objective measure of the effectiveness of your training plan. Heart rate will let you know you are alive.
Direct vs. Indirect
Power (Watts) is a direct measure of exercise intensity, whereas heart rate is an indirect measure of exercise intensity. Heart rate is a response to exercise and other factors (heat, humidity, altitude, diet, caffeine, stimulation, motivation, fatigue, time of day/night).
Crystal Clear vs. Crystal Ball?
Performance is accurately measured with power. Power data is crystal clear. You either produced the watts or you did not. Heart rate data requires guess work to interpret the result due to the many variables included. A crystal ball may be helpful in order to draw real conclusions from heart rate data.
Immediate vs. Time Lagged
Power has an immediate reaction to changes in exercise intensity. Heart rate has a time lag of about 30 seconds in its response to changes in exercise intensity. This makes heart rate a useless pacing tool for efforts of less than 30 seconds and for the first 30 seconds of any longer interval. Heart rate encourages athletes to over-pace at the start of an interval in order to quickly get their heart rate into the target zone. When training with power you can immediately peg the exact goal exercise intensity and train with accuracy.
Here’s an example: The goal in the following workout was to maintain a steady power of 265 Watts. The rider also wore a heart rate strap, so we have both sets of data.
Not only does heart rate lag effort by 30 seconds, it can also creep upward over time. Imagine if this rider didn’t have the benefit of the power readings, and instead attempted to drive HR up to 165bpm in the first few minutes. The result would likely have been an interval ending meltdown about 18 minutes in, and at the very least a drastic reduction in power in the 2nd half of the interval.
There are several software applications available to crunch your power data. They will analyze, interpret and summarize. You can look at how fast and hard you are pedaling with Quadrant Analysis (QA) to see if you are mimicking the demands of racing in your training. You can get a measure of the intensity of a ride (IF), the variability of a ride (VI) and the training stress (TSS) of a ride.
Performance Manager Chart (PMC)
PMC is a valuable tool for mountain bikers. It uses ride TSS scores, averaging them over days and months. Analyzing a single ride is like looking at a single tree in a forest. You get a nice picture of that tree but don’t know where it sits in the forest. The beauty of the PMC is that it tallies up TSS over time to give a bird’s eye view of the forest – or your entire season (or even cycling career). The PMC can be used retroactively to look at scores during times you had personal best performances and during times you thought you should have but didn’t. It can be used for forward planning to target a specific set of scores known to put you in peak form and to time that peak form to land smack bang on race day. The PMC takes much of the guess work out of training, tapering and peaking.
Whether or not to race with a power meter depends on the priority of your race. In low priority training races, go for the power meter. Race data often uncovers one’s strengths and weaknesses, and can also turn up some surprising finds with regards to race demands. Race files are a powerful piece of the training puzzle.
As an example, using Quadrant Analysis (a feature of WKO+ 3.0) with power meter data from single speed mountain bike races shows a particularly high concentration of power in the VO2max range with cadences below 60. This means pedal forces are much higher on average than when riding with gears. This has led to some novel training methods for single speeders.
Goal events are different. By the time you have reached a fitness peak, all those hours of training with a power meter have worked to “calibrate” your perceived exertion (PE). PE is your best option for pacing goal events. You’ll know what you can do and for how long, and with enough experience, PE alone will guide you to your best results.
Potential drawbacks to mountain bike racing with a power meter
Power meter and heart rate monitors are not 100% reliable. How will you pace the event if your gadget malfunctions?
Power meters are heavier than race-weight wheels or cranks.
The highly variable nature of power production in mountain bike races makes it quite difficult to turn the real time power data into actionable information. Short accelerations and race starts are deep into anaerobic power levels, even for longer endurance events. It is tough to make sense of the numbers without software.
Mountain bike race starts are mayhem. The place for your eyeballs during a race start is on the trail, your surroundings and fellow racers and not on a little monitor screen.
Power meters can even make you slower in a peak race!
More importantly, pacing with a power meter may actually hold you back from a breakthrough performance! On a top priority race day your body should be in peak condition; trained, tapered, fueled, hydrated and ready to go. You should be poised to set records by producing more power and going faster than ever before. Pacing yourself using power numbers established in training may act as a governor on your peak day and could hold you back from a potential record performance.
Post Race Analysis
There is often quite a difference between what you think you did in a race (or, what you tell your coach you did) and what you actually did. Power data tells all! You can learn how to pace races more accurately and how to repeat outstanding performances from the data. Race data is useful in learning how much power you needed to win a certain race and in what pattern that power was created. This type of information is valuable in order to design better training plans and improve future performances.
Without a doubt, train with a power meter. Also, race your lower priority events with the power meter to help objectively assess your strengths and weaknesses, helping you dial in your training for the goal event(s). For peak priority races use your lightweight race equipment and rely on a well calibrated sense of PE to reach new performance heights.