Garmin Forerunner 645 Running Watch

Although it has some populist features, like the music player and cardless pay option, this watch is built for runners. Even in GPS mode, the battery gives you up to 14 hours between charges. Sensors include the optical wrist-based heart rate, as well as a pulse oximeter which tells you the percentage of oxygen in your blood. Until recently, pulse oximeters were rarely seen outside of hospitals. Runners use O2 saturation to tell them how effectively their blood is moving oxygen throughout their bodies. Noticing a sudden drop in oxygen levels could prevent a serious incident.

Other runner-specific stats include recovery time or the amount of time it takes for your heart to return to its typical pulse rate after the activity that causes the heart rate to increase. Speedy recovery time can be an indicator of good heart health. It's an example of one of the very specific training goals this watch makes possible. Distance runners have long looked at resting heart rate as a metric for the effectiveness of their training, with a lower resting heart rate as the goal.

In addition to resting heart rate and recovery time, the optic wrist sensor also gives you heart rate zones, alerts during runs, calories burned by heart rate, and maximum heart rate post-run. There are even more heart metrics, so many that it's difficult to describe them all.

Other cool things this watch can do include ground contact time, stride length, run cadence, and a race predictor. The race predictor attempts to forecast your performance in a race based on your recent metrics during training. It's a fun way to challenge and compete with yourself, and you can also challenge friends with one of the dozens of different apps that are all compatible with the watch.

Just from looking at the most basic specs, it's obvious that the Garmin Forerunner 645 caters to serious, experienced runners. Cadence, stride length, and ground contact will not mean much to recreational runners or those of us just starting out. In this next section, we'll break down some of the specific technical stats and explore more of what you can do with this watch. If you are thinking of purchasing, though, do yourself a favor and hit the product page on Garmin's website first. It is easy to find and goes into greater detail than we are able to here.

All specs come from the Forerunner 645 product page on Garmin's website. To save space, we're going to list each spec with a brief description, instead of summarizing and giving a rundown on each like we normally do. We'll do a wrap at the end of this section. As accurate as we have tried to be, know that this isn't even a complete list. There is just so much the 645 can do. Our goal is to give you a thorough but brief snapshot.

Lens: Corning Gorilla Glass
Quick-release bands for removing or customizing the band
Silicone strap fits 5 to 8-inch wrists
1.2-inch screen with 240 by 240 resolution (in pixels)
Weighs about 42 grams with factory strap (less than 1.5 ounces)
Holds up to 200 hours of movement history

Fully functional clock with stopwatch, timer, alarm clock, and sunset/sunrise tables
9 onboard sensors, including GPS, GLONASS, Galileo, heart rate sensor, compass, gyroscope, and thermometer
Connect IQ app lets you change look and layout of watch for quick customization
Bluetooth, ANT+, and Wi-Fi compatibility
Calendar, weather (without an extra app), Find My Phone/Find My Watch safety feature
Camera remote controls the camera on your phone
Garmin Pay capability

Activity modes include indoor cardio, strength/gym workouts, yoga, and all different kinds of running. The watch will work on a treadmill as well as it will outside. These non-running activity modes are a concession to non-runners who may want to use the watch, as well as those whose center is running but who also like to cross-train.

Our only gripe about this is the yoga tracking mode. We're mostly old granola ladies, so we believe yoga practice is a time to disengage completely and clear your mind of whatever is in it by getting attuned to your body. For us, that means leaving the watch in your locker with the phone. But not everyone feels the way we do, and even we know how to turn off or disable features if we don't want them. The other great thing about this watch is how easy and intuitive it is to use, even when dealing with more advanced settings and metrics. We'll discuss more ease of use in the next section.

Although you may expect a responsive touchscreen on a watch this expensive, reviewers we found agreed it's still quite easy to navigate and read even during activity. There are five buttons, on the sides, that you can use to scroll through menus, reject phone calls, and build your ultimate run playlist once you connect Spotify.

To confirm what we read, we looked up the 645 user's manual. It is easy to find through Google, living on the Garmin website and a number of mirror sites. However, you find it, previewing the user's manual is a great way to guide a purchase decision for this watch or most any fitness product you could want. If the directions are poorly written or overly complex, you can look elsewhere for a similar product.

A button on the top left both powers the watch on and engages the vibrant backlight which lets you read and select even in the dark. All buttons are big enough to always find, and you won't fumble and press two buttons at once. You start the activity with a button on the right and push the same button to pause activity so you can read a message or perform another non-exercise task.

You also get a back button that doubles as a split lap switch and a down button for scrolling. Finally, the bottom right button lets you see the main menu. This button also lets you access settings and widgets.

If you've ever used an old school digital stopwatch, we think you'll be able to navigate the Garmin Forerunner 645. It is exponentially more complex, but the designers made easy-touch traditional buttons to steer through it all. Don't worry, though--you don't have to read a step like "hold down button X while pulsing button 3 for exactly 7 seconds to access alarm." We've bought watches like that, too. Everything about the Garmin Forerunner 645 is intuitive and user-friendly, just as you'd expect from an industry veteran like Garmin.

The Garmin Forerunner 645 Music watch is expensive, but worth it for runners who need detailed data like stride analysis. General fitness buffs will not want to spend the money on something with more than they need, though Garmin did add other activity trackers like yoga, weightlifting, and indoor cardio. The watch can hold up to 500 songs from Spotify music for playback but is not compatible with any other music player. Rather than a touch screen, Garmin added five push buttons that are easy to learn and use. You can use the buttons to scroll through the intuitive menus. Though there isn't as much here for general users, those of us who pursue running as a passion will love this watch and will see training benefits almost immediately.