Best heart rate monitors for triathlon and endurance training

I spent most of last summer training by feel. Perceived effort, breathing patterns, just vibes. It worked okay until I blew up twenty minutes into the bike leg of a sprint triathlon because I’d gone out way too hard on the swim and had no idea my heart rate was already through the roof. That was the race that convinced me to actually pay attention to my heart rate data instead of guessing.

If you train for triathlon or any endurance sport, heart rate is one of the most useful metrics you can track. It tells you whether you’re actually in Zone 2 on easy days (most of us aren’t) and whether your intervals are hitting the right intensity. A good triathlon watch will show you the numbers, but the accuracy depends entirely on the sensor feeding it.

The short version: chest straps are still the most accurate option. Optical arm bands have gotten surprisingly close. And wrist-based sensors on watches and trackers are fine for steady-state cardio but tend to struggle with anything involving fast heart rate changes or wrist movement. Here are the monitors I’ve tested and recommend.

Chest straps

Polar H10, $90

The Polar H10 has been the benchmark for heart rate accuracy for years, and nothing has really knocked it off that spot. I’ve worn this strap through pool swims, outdoor rides, and tempo runs, and it consistently matches up with what I’d expect from my effort level. It locks onto your heart rate fast and doesn’t drop signal during transitions or when you’re moving between activities.

The strap itself is a soft textile material that’s comfortable enough to forget about mid-workout, though I’ll admit chest straps in general take some getting used to if you’ve never worn one. The dual Bluetooth and ANT+ connectivity means it pairs with basically everything: Garmin watches, Wahoo bike computers, Peloton bikes, gym equipment, phone apps. It also has onboard memory, so you can swim without your watch and sync the data later.

The one real knock on chest straps is that some people just don’t like wearing them. If you find them uncomfortable or they slip during certain movements, that’s a legitimate reason to look at the arm band options below. But if accuracy is what matters most to you, this is the one to get.

Garmin HRM-Pro Plus, $130

The Garmin HRM-Pro Plus costs about $40 more than the Polar H10, and the accuracy is essentially identical. So why pay more? Running dynamics. If you’re a Garmin user, this strap feeds your watch data on cadence, ground contact time, vertical oscillation, and stride length. That data is useful if you’re working on your running form or trying to figure out why you keep fading in the last few miles.

It also stores heart rate data during swims and syncs it to your Garmin watch afterward, which is a nice touch for tracking training load across all three disciplines. The strap material feels similar to the Polar, and battery life is solid at about a year of regular use with a replaceable coin cell.

The catch is that most of those running dynamics features only work within the Garmin ecosystem. If you’re using a COROS or Suunto watch, you’re paying extra for features you can’t access. For Garmin users training for triathlon, though, it’s worth the premium.

Wahoo TICKR X, $80

The Wahoo TICKR X sits right between the Polar and Garmin in terms of features and slightly below on price. Accuracy is very close to both, maybe a beat or two off during really sharp intervals, but nothing you’d notice in normal training. I’ve found it particularly reliable on the bike, where it pairs well with Wahoo’s ecosystem of trainers and computers.

The TICKR X has its own motion analytics and built-in memory, plus dual Bluetooth/ANT+ (which every chest strap should have by now). It’s noticeably lighter than the Garmin strap, which some people appreciate on long runs. Wahoo’s app is straightforward if you want to use it standalone, but it also plays nice with third-party apps like TrainingPeaks and Strava.

If you don’t need Garmin’s running dynamics and just want a reliable chest strap that works with everything, the TICKR X is where I’d start.

Arm band monitors

COROS heart rate monitor, $80

The COROS arm band is the monitor that surprised me the most. Optical sensors have historically been a step behind chest straps, but this one tested within a couple of beats per minute of my Polar H10 across running, cycling, and even some strength work. You wear it on your upper arm, where blood flow is more consistent than at the wrist, and that seems to make a real difference in accuracy.

Battery life is 38 hours of continuous use, which in practice means you can go weeks between charges if you’re training an hour or two a day. It also has auto-wear detection, so it turns on and starts broadcasting when you slide it on your arm. It connects via Bluetooth to up to three devices simultaneously, which is handy if you want your watch and your bike computer reading the same source.

The downside compared to a chest strap is that you still need to position it correctly on your bicep for the best readings. Too loose and you’ll get noise in the data. It also can’t match a chest strap for very fast heart rate changes during short, explosive intervals. But for steady-state endurance work, which is most of triathlon training, it’s excellent.

Wrist-based trackers

Fitbit Charge 6, $130

I’m including the Fitbit Charge 6 here for a specific reason: it’s a solid entry point if you’re just getting into structured training and aren’t ready to invest in a dedicated monitor plus a GPS watch. The Charge 6 gives you continuous heart rate tracking, built-in GPS, sleep data, and compatibility with gym equipment that supports Bluetooth heart rate, all in one wrist band.

For easy runs and steady bike rides, the optical wrist sensor does a reasonable job. It tends to lag behind chest straps at the start of workouts and can lose the plot during fast transitions or activities with a lot of arm movement. Swimming tracking exists but isn’t its strong suit. If you’re training for your first sprint tri and want something simple, it works. If you’re doing structured interval sessions where you need to nail specific heart rate zones, you’ll outgrow it.

The Google and Fitbit app ecosystem covers general health and fitness tracking well enough, though serious triathletes will eventually want something that talks to TrainingPeaks.

What I’d buy

The Polar H10 at $90 is what I recommend to most triathletes. Accurate, compatible with everything, and the onboard memory handles pool swims where your watch can’t maintain a connection. I’ve been using one for over a year and haven’t found a reason to switch.

Garmin users who want running form data should look at the Garmin HRM-Pro Plus. The running dynamics have actually helped me spot some stride issues I wouldn’t have noticed on my own. At $130 it costs more, but the extra data is worth it if you’re already in that ecosystem.

Chest straps not your thing? The COROS arm band gets you surprisingly close to chest strap accuracy at $80. That 38-hour battery is a nice bonus too.

The Fitbit Charge 6 works as a starting point if you’re new to structured training and not ready to buy separate devices. Just expect to outgrow it once you start doing real interval work.