I still remember how excited I was to buy my first bike computer and heart rate monitor. I immediately plugged in my HR zones and started tracking my data using an Excel spreadsheet. Then I got a “dumb” trainer and would use HR to train to videos. I felt official when I began using TrainingPeaks to monitor my metrics.
At that time, I was inexperienced and unknowledgeable about heart rate drift, heart rate TSS, and heart rate variability. I would train to heart rate, regardless of how I felt. As a result, there were many years I felt overtrained and fatigued.
Then the power meter arrived. I was enthralled but swore to myself that I would never buy a tool that expensive for cycling. Hell, I wasn’t a pro or anything! I continued to pedal towards my goals using heart rate. Over time, I found that accurately tracking TSS with only heart rate could be problematic, especially with the varied nature of mountain biking. There were many days I would ride mountain bikes for two hours with friends, only to find that I worked way harder than I needed to. I also noticed a considerable difference in hrTSS, especially when skate skiing and mountain biking compared to road cycling.
I finally bit the bullet and purchased my first hub power meter. I spent two solid years of training and racing using this new tool and began to understand its importance when comparing heart rate to RPE. While both HR and power provide a unique lens for understanding physiological demands, I believe HR is a secondary metric to power. I found power to be critical in the structure, design, and evaluation of my workouts, which became much more manageable and specific, especially on the trainers and the road.
Now I feel naked when I ride without power. I have found that power meters are especially important when executing short interval workouts and keeping within specific power ranges. Over time, I have even been able to moderate the intensity of my mountain bike rides to keep them in line with my other cycling training.
I wanted to share some tips on what I have learned in the past few years using power meters on all of my bikes.
Helps Monitor Your Workouts
Due to the terrain, mountain biking is so variable that trying to stay within a prescribed zone is enough to drive you crazy. Ensuring you have the right settings on your computer can help you monitor your rides more accurately. Head unit settings I recommend are target power, current lap, 10-second power, 30-second power, Normalized Power, Lap Power, Heart Rate, and Cadence.
Over time you will get a feel for how hard you need to be going based on these metrics, especially on those mountain bike rides that take over two hours or so. For example, when I execute a zone 2 endurance ride of 193 watts, I monitor and compare my lap power and norm power to my target power. If my norm and lap power are higher than I know, I need to back down on my 30-second average power, which is typically on the climbs. I confirm all these numbers using my heart rate.
Adds Context to Heart Rate Data
Heart rate is just one piece of the puzzle and is impacted by many factors such as temperature, environment and body temperature. Heart rate can be compared to the tachometer in your car; the more you step on the gas pedal, the higher the RPMs go. On the other hand, power measures your “horsepower” on the bike in the form of watts. By comparing heart rate response with power output, you can determine your level of fatigue.
For example, if you want to complete 3 x 10 sub-threshold intervals at 215 watts and find your heart rate only getting up to 120 bpm, this may be an indicator you are fatigued and need some rest.
Having a power meter on all of your bikes also lets you make “apples-to-apples” comparisons to rides and TSS scores. You will find massive variances in IF and TSS between your mountain bike rides and road rides. Over time, you will know which workouts to best execute on each bike. For example, I find threshold intervals are best done on a trainer or road bike, whereas longer sub-threshold and endurance rides can be effectively done on a mountain bike.
Helps Dial In Your Nutrition
Monitoring nutrition is difficult to do, especially in the excitement and adrenaline of a race or event. Most athletes underestimate their caloric needs, only to find they did not eat enough towards the end of the race. Here is what we do know: riding uses energy in the form of kilojoules.
If you don’t monitor kilojoules, you’ll have to “best guess” your caloric intake, and getting it wrong can result in a decrease in the production of watts. Fortunately, power meters can measure kilojoule expenditures. Using Kilojoules (nearly a one-to-one ratio with calories), we can determine whether to consume additional calories or cut back.
Reviewing the total energy expenditure in kilojoules for the entire ride can allow an athlete to set goals for caloric intake in each segment. Take the time to learn when to eat, how much to eat, and which electrolyte replacement to use. Using your power meter and the kilojoule readings, you can make a better estimate of the correct levels of carbohydrate intake during events.
I can’t emphasize enough that power meters on your bikes are a game-changer. If you are going to invest time and money into training, coaching, race fees, and bike equipment, it only makes sense to have power meters on your bikes. It is guaranteed to make the most effective and efficient use of your training time.
