Benefits of a Heart Rate Monitor, and Which Type to Buy

A heart rate monitor shows how hard you are really working, so you can keep easy cardio easy, push intervals hard enough and spot poor recovery. Chest straps are the most accurate during training because they read your heart’s electrical signal. Wrist watches are fine for steady cardio and daily tracking but less reliable during lifting and intervals.

Why use a heart rate monitor at all?

Your sense of effort lies. People who think they are doing easy cardio are often working too hard, and people who think they are doing intervals are often not working hard enough. A monitor fixes that.

What it helps with:

• Keeping Zone 2 sessions in Zone 2, roughly 60 to 70 percent of max heart rate
• Hitting the right effort on intervals
• Tracking fitness over time. Your heart rate at the same pace drops as you get fitter.
• Seeing poor recovery. A resting heart rate that is higher than usual for several days is a sign to back off.
• Pacing walks and runs for fat loss. See will walking help me lose weight.

Are chest straps more accurate than wrist monitors?

Yes, especially during hard or jerky movement. In a study of popular wearables during treadmill, bike and elliptical work, the chest strap was the most accurate and wrist devices varied a lot, particularly at higher intensities (Gillinov et al., 2017).

Wrist monitors use light to read blood flow under your skin. Sweat, movement, a loose band, tattoos and gripping a bar all throw them off. Chest straps read the electrical signal from your heart, so they hold up better during intervals and lifting.

Are the calorie numbers on fitness trackers accurate?

Not very. A Stanford study found wrist devices measured heart rate reasonably well, but none of the seven devices tested measured calories burned accurately (Shcherbina et al., 2017). Use calorie numbers as a rough comparison between your own workouts, not as permission to eat more.

What did I learn from the Adidas FitSmart, Polar A300 and Polar M400?

I reviewed these three back around 2015. They are old models now, but what I learned still applies.

• Adidas FitSmart. My worst experience. The battery died mid-workout, the charging cable was proprietary and easy to lose, syncing to my phone barely worked, it was not waterproof, and the strap broke after about three weeks. The wrist sensor could not keep up during hard intervals. Lesson: brand name does not equal quality.
• Polar A300. A solid basic tracker. It plugged straight into USB, tracked daily steps, gave a fitness test estimate and worked with Polar’s app. The band felt flimsy, but Polar sold replacements. It was a big step up from the older FT60.
• Polar M400. The best of the three. It added GPS, standard micro-USB charging, water resistance for swimming, sleep tracking and inactivity alerts. It felt like a real training watch.

The lesson from all three: pick a device for accuracy and reliability first, features second.

Which heart rate monitor should I buy now?

These are the types I recommend to clients. Models change every year, so check current versions and prices before you buy.

• A basic chest strap like the Polar H10. My pick for accuracy. It pairs with most watches, phones and gym equipment.
• A chest strap with running data, like Garmin’s HRM-Pro line, if you already use a Garmin watch and want running dynamics.
• A rechargeable chest strap, like the Wahoo TRACKR, if you hate replacing coin batteries.
• An arm band or switchable sensor, like the Myzone MZ-Switch, if chest straps bother you. Upper arm optical sensors are usually more reliable than wrist sensors.
• A GPS watch from Garmin, Polar, Apple or similar for daily steps, sleep and steady cardio. Pair it with a chest strap for interval days.

How do I use heart rate zones?

A simple version based on estimated max heart rate:

• Zone 1, 50 to 60 percent: warm-ups and recovery walks
• Zone 2, 60 to 70 percent: most of your cardio. You can still talk in full sentences.
• Zone 3, 70 to 80 percent: steady hard work
• Zone 4, 80 to 90 percent: intervals
• Zone 5, 90 percent and up: short sprints

Age-based formulas like 220 minus your age are only rough estimates. If your numbers feel off, go by breathing and talk test. For fat loss, put most of your cardio in Zone 2 and add a little Zone 4. More in is steady state cardio worth it.

If you want cardio zones built into a full plan for your body type, take the XPL quiz.