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Wondering whether you should train with power data, a heart rate monitor, or both to effectively improve your performance? I asked myself the same question before investing in these devices. After reading dozens of articles, talking with pro cyclists, and doing some training myself, I’ve summarized everything I learned in this article.
KEY TAKEAWAY
The main difference between a power meter and a heart rate monitor is that the power meter provides objective, instantaneous data about your effort. Heart rate monitors measure heart rate, a lagging indicator of your body’s response to a given effort, and can be influenced by other factors like fatigue. The best practice is to use them both and analyze the data during and after the training.
Let me explain this in more depth below.
Power Meter Data: Instant and Objective
Power meters provide real-time, objective, and accurate data that eliminate guesswork.
Take a look at the following snapshot from my structured workout.
You can see that the power data (yellow line) are instantaneous, while the heart rate changes with a delay, e.g., my body’s response (red line). The implication is that interval training based on your HR is limiting and inaccurate.
Today’s power meters have an accuracy between ±1% and ±3% (source), which is sufficient for most riders, including pros.
Power meter consistency is no less important, though. It gives you the same consistent data in various conditions (altitude, temperature, etc.).
The following table shows the power deviations of multiple accuracy rates and power outputs.
| Accuracy Rate / Power Output | 250W | 500W | 1000W |
|---|---|---|---|
| 0.5% | 248.8-251.3 | 497.5-502.5 | 502.5-1005 |
| 1% | 247.5-252.5 | 495-505 | 990-1010 |
| 1.5% | 246.3-253.8 | 492.5-507.5 | 985-1015 |
| 2% | 245-255 | 490-510 | 980-1020 |
| 2.5% | 243.8-256.3 | 487.5-512.5 | 975-1025 |
| 3% | 242.5-257.5 | 485-515 | 970-1030 |
Power meters are also better than HR monitors for tracking long-term progress and can show advanced metrics like your left/right leg balance.
On the other hand, they are more expensive, and their data are more difficult to interpret, so you may need a consultation with an experienced trainer.
Are you still not sure if power meters are worth it? Then, check out more reasons to use a power meter.
Heart Rate: Delayed and Subjective
Heart rate monitors are affordable and easy to use, and their data are easy to interpret. The problem with heart rate is that it just shows your body’s response to a given effort. It is delayed and doesn’t tell you precisely what work (power) you are doing. Heart rate also varies based on multiple factors such as:
- Fatigue
- Age
- Diet
- Outside temperature
- Stress
- and more
That’s why the HR data are subjective. So, does this mean they are useless?
Not quite. However, cyclists shifted from ‘training by heart rate’ to ‘training by power with heart rate.’ This is because HR will provide you with information about your body and complement the power data so you (or your coach) can make more educated decisions.
Check out the summary of the pros and cons of power meters and HR monitors.
| Device | Pros | Cons |
|---|---|---|
| Power Meters | • Measure your efforts instantaneously (without lag) • Objective (not influenced by external factors) • Better for tracking your long-term progress • More expensive models can show leg imbalances | • More expensive • More difficult to understand and interpret the data • Some power meters need regular calibration |
| HR Monitors | • Less expensive • Easy to use • Easy to understand the data | • HR lag • HR may be affected by external factors like fatigue, air temperature, sleep quality, etc. • HR straps may be uncomfortable |
Sources: roadcyclinguk.com, bikeradar.com, trainerroad.com
I also recommend watching the following video by Dylan Johnson. It includes much well-researched information.
Conclusion
Invest in both devices if you are serious about your training and want to take it to the next level.
A power meter will provide you with real-time, accurate data you can rely on (browse the best power meters on the market, from budget ones to premium ones).
A heart rate monitor will inform you how your body reacts to a given effort. In addition, it is more affordable, so it won’t ruin your budget.
Remember, though, the most important thing is to interpret the data you get from these devices correctly. It can be a little overwhelming for beginners, so I recommend consulting them with a professional coach.
