Measuring heart rate and power

The intersection of gear that gets the most out of your training.

Photo: Phil Walter/Getty Images

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By now you know that heart rate and power are two measurements that can improve your training. The larger question of how to gather that data, and what you should do with it, looms larger. The gathering part of the question is actually quite simple. The interpretation part is more difficult to understand.

Heart rate vs. power

The meanings of two most important metrics for your training are often conflated. Your heart rate and your power measure two very different parts of your performance. Simply stated: Heart rate measures what’s happening inside your body, while power measures what your body is putting out.

“Heart rate is an internal metric — it gives clues to what’s going on with your body,” says Trevor Connor, CEO of Fast Labs, LLC and The Paleo Diet, LLC. “But it doesn’t say anything about how fast you are going. You could have two riders of the same weight with the same max heart rate riding at 150 BPM and say that they are experiencing a similar physiological response. But one could be a pro riding at 300 watts while the other could be an amateur riding at 180 watts.

“Power is an external metric — it shows what’s going into the bike, or how hard you are going relative to others. But saying someone is riding at 200 watts says nothing about how hard they are going physiologically. It’s a subtle difference because we have found ways to translate back and forth, but power still has limits in terms of showing what’s going on physiologically and vice versa. Ultimately this is why it’s so powerful to use both in conjunction.”

The intersection of those two metrics provide insight into how you are progressing as a cyclist. Used individually, you only get parts of the story. By using both, and interpreting where that data matches up, you get a more complete picture of your overall performance.

“We set heart rate zones and calculate our threshold power and heart rate,” says Connor of the athletes he works with. “But those numbers can fluctuate. Fatigue, heat, dehydration, stress, sleep, food, and many other factors can affect them. You have to assess yourself every day and adjust the numbers when you can tell they are off (i.e., you can tell your heart rate is depressed one day.) If you lose that and try to be a slave to a specific number, you’re going to do a lot of less-than-optimal training.”

The gear you need

In order to capture that data, you need two basic tools: a power meter and a heart rate monitor.

There are two general types of heart rate monitors: chest straps and optical units. A chest heart rate strap tracks your heart’s electrical activity and transmits a radio signal to your recording device. An optical heart rate monitor is often worn on the wrist or forearm, and it sends LED lights through the skin and records how the light bounces off your blood vessels. In essence, this type of meter is measuring your blood flow. This then transmits data to your recording device.

Until recently, chest straps (electrical) were considered far more reliable than optical monitors. But optical heart rate monitor performance has improved drastically, and Wahoo’s Tickr Fit addresses one of the shortcomings of optical monitors by placing it on the forearm rather than at the wrist. This creates a better connection between the monitor and your body so there are fewer gaps in heart rate measurement. Many optical monitors live in wristwatches, and the connection at the wrist can sometimes be tenuous.

Power meters measure your output force. The most popular power meters are integrated within or affixed to the crank arms, and they contain strain gauges that deform as you apply force to the pedals. The measurement of that deformation is then sent to your GPS head unit and displayed as a wattage reading.

So you’ve got the tools. Now what?

“One thing that can always help lead in good directions is to look for trends,” says Connor. “One-off numbers, such as peak 5-minute power, or a hard workout that causes the software to raise your FTP, are nice to see, but they are isolated events. Look for the trends in your numbers over weeks and months. I have a graph where I track my athletes’ trends in five minute power over both the previous year and the last 28 days compared to the same 28 day period the previous year. Those trends can tell a lot, and more importantly I’ve noticed they tend to match up with the sense the athlete has about themselves.”

Of course, to the casual rider, it may not be necessary to spend money on these tools at all. It’s possible to get fit and achieve your goals without them, provided your goal isn’t to win races.

But if you’re going to invest in one, you should probably invest in the other, too. “It’s always a question of budget,” says Connor. “I’m careful not to tell an athlete that they must get a power meter when money is tight and they aren’t racing or training at a level where one is crucial. But if money is not a concern then I definitely feel an athlete should have both a power meter and a heart rate monitor. I don’t feel either gives a complete picture on its own. You get the full picture from both.”

Leomo type-s
The Type-S from Leomo tracks you biomechanics. Photo: Courtesy Leomo


There are tools beyond the heart rate monitor and the power meter that can help you improve your  performance. They aren’t necessary, but they can be useful for specific goals.

Leomo’s Type-S computer, for example, tracks your biomechanics and shows where you might be losing power in your pedal stroke, how you might improve your body position, and much more. If you’re recovering from injury, this can be a useful tool — provided you consult a professional who can help you interpret the data before making any adjustments to your movements.

“I really like the Whoop strap because it helps add recovery to the equation,” says Connor. Indeed, rest is perhaps the most overlooked training tool in an athlete’s arsenal. The Whoop Strap, and other devices like Polar’s Ignite watch, can deliver data on how restful your sleep was, and how hard you worked during your last ride or workout.


There are enough gadgets measuring a plethora of different analytics to boggle the mind. It’s easy to get overwhelmed, so Connor recommends simplifying. Start by focusing on the relationship between your heart rate and your power, and learn to listen to your body.

When it comes to training gear, you can do a lot with a little. If you do choose to invest in a power meter, make sure to use heart rate in conjunction with power data to get the most accurate picture of your progress. “I think looking at the relationship of power to heart rate is important,” says Connor. “A sudden drop in heart rate relative to power can indicate fatigue. A gradual rise in heart rate relative to power over the course of a ride (called cardiac drift) can indicate fatigue, a lack of sustainable endurance, that the ride is too hard, or simply that you’re dehydrated.”

He also recommends using the 3-second power reading on your computer to get a better sense of your true power output. Anything less than that can fluctuate too much to be useful for your training.

If you find yourself obsessing over numbers, you’re probably doing more harm to your training than good. It’s still important to track that data, but Connor recommends throwing your GPS computer in your pocket and forgetting about it on your ride. That way you get the data without the obsession.

And if you don’t want to spend a dime, you can still improve your performance by kicking your legs up and resting.

Power Gear

Must-haves for training with power and heart rate.

Wahoo Tickr Fit arm band

Wahoo Tickr Fit heart rate arm band $80

This optical heart rate monitor fits comfortably around your forearm for those that dislike the feeling of a chest band. It’s easy to pair, with single-button operation.

Single-sided power meters from Stages

Stages single-sided power meter $300 and up

Still one of the best deals on power meters, a Stages single-sided meter gives you plenty of features at a reasonable pricepoint. If you’re looking to buy your first power meter, start here.

Whoop strap 3.0

Whoop Strap 3.0 $18/mo and up

Lightweight, waterproof, and packed with data: The Whoop Strap tracks data 24 hours a day to give you a better understanding of your strain, and your recovery.

An American in France

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