I have never used or owned a fitness tracker. If I’m running, I wear a GPS watch. If I’m biking, I have a bike computer. If I’m doing anything else, well, I can always look at a clock. But Fitbit’s improved ability to track all your activities and stats, and then sync them into one spot was interesting to me.

Two new upgraded Fitbit devices—the Charge 2 and Flex 2—officially launch on Aug. 29, and we got a preview to test them out over the last few days. An upgraded app experience with guided runs, known as Fitbit Adventures, will be coming as well.

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Charge 2

The new Charge 2 ($149) is an update of the Charge HR—so it still has the built-in wrist-based heart rate and automatic activity tracking of steps, calories, elevation, and sleep.

What it’s added is an expanded ability to recognize specific workouts. You can set a handful of activities like running, biking, weights, treadmill, or yoga. Then simply hold down the start button while in that activity screen and press stop when you’re done. If you forget to press start/stop, it automatically recognizes most activities after about 10-15 minutes. This is not a flawless system, but is a nice backup. The Charge 2 also syncs with the GPS in your phone to measure pace and distance—which you are now able to see on the watch screen while working out.

I had mixed results with these workout functions, which are admittedly not necessarily designed for high-performance. A 40-minute run, which I did without my phone’s GPS, was surprisingly accurate in terms of distance and pace. It wasn’t precisely accurate, but, given it was only operating off-stride length, I was impressed. Conversely, I was unimpressed with a cycling workout I did while using the GPS on my phone to sync. The GPS went out about 40 minutes into a three-hour ride—which isn’t Fitbit’s fault, but likely my phone carrier’s doing—but I would have expected the Charge 2 to recognize I was still in cycling mode and to pick the GPS back up later. Instead, it told me I had ridden just 8 miles in three hours and that I had somehow walked nearly 6,000 steps while riding my bike. This seems like a mistake.

My only other pet peeve with the workout functions was that I couldn’t figure out how to pause a workout without stopping it completely, and I’d prefer to be able to look down at the screen and have it always on, instead of having to tap it or turn my wrist to kick-in the auto-on. But plenty of people will likely have no issue with either of these things.

What I was mainly curious about was being able to see the calorie, sleep, and heart rate data over time to spot trends or patterns. I was particularly interested in a new feature in the Charge 2 that calculates what it calls your Cardio Fitness Score, which is essentially an approximate VO2 max, or a measurement of the maximum amount of oxygen an athlete is capable of using.

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According to Fitbit’s product developers, the Charge 2 calculates this score by using your resting heart rate patterns and heart rate during workouts. When compared with lab VO2 max tests, they said the Cardio Fitness Score is highly accurate. Once you do a run (or a few runs) with the GPS on your phone, and the device has more data to work with, it narrows down and improves its calculation. For runners, this is a useful piece of data, particularly if you can see how you improve, or don’t improve, over time and with training. For people who are not familiar with VO2 max, the Charge 2 also tells you how you fit within the appropriate demographic range and gives you suggestions on how to improve.

The heart rate data seems, on the whole, fairly accurate. Generally speaking, my heart rate has been about right for my runs (130-150 bpm) and bike rides (around 120 bpm), and my resting heart rate sitting on the couch seems correct (50-60 bpm). At times, though, it goes blank and sometimes there is a lag before the heart rate numbers go up or down. For example, when biking up a very steep hill my heart rate still read 93 bpm, which is unlikely.

(The caveat on heart rate data is that you don’t necessarily know why your heart is doing what it’s doing. And, at some point, a high resting heart rate could be as much an indicator of overtraining as of under training. But, for the general user, this isn’t likely an issue.)

I haven’t been able to get the Charge 2 to give me a Cardio Fitness Score yet, though, because it hasn’t been able to get the data it needs, and because of issues noted below.

As a watch, it’s exactly the kind I would wear: relatively small and sleek-looking. There are also a range of bands you can choose from and digital watch faces. And it now gives you text message and calendar alerts, in addition to caller ID. You can set alarms and reminders to move, which will light up and/or vibrate on the watch.

It’s currently not doing me much good as a watch, though, because I’m traveling and I can not get it to update the time zone. No matter how many times I manually change the time zone in the app, restart, and re-sync the device, it still gives me the wrong time on the watch. (It’s correct in the app.) A perusal of the Fitbit help board suggests I am not the only one who’s had this problem with older Charge devices. This is becoming slightly maddening since the two devices, the app, and the desktop dashboard can’t agree on a time, meaning my stats and activities are being attributed to different days.

Probably I should just relax and go through the new guided mediation/relaxation mode on the Charge 2, which uses your heart rate and heart rate variability to guide you through a two-minute breathing exercise.

The battery lasts five days and I’ve had no issues. Once I can get it to recognize my time zone, it actually seems like it will be fairly useful, not as a replacement for my bike computer, but as additional information. Or, if you’re not as obsessed as I am with a variety of workout details, but want an overall accounting of your health and activity, then you’d likely find the Charge 2 more than enough and a lot more convenient.

Flex 2

The Flex 2 ($99) is 30 percent slimmer and lighter than the original Flex band. In fact, if you often have a few hairbands around your wrist, then the new Flex 2 blends right in.

Since the Flex 2 is still in beta, I can’t provide a full review. But what it is offering is a new swim mode, which also means it’s waterproof, so you don’t need to worry about it getting wet in the shower or washing dishes. The device has increased auto exercise recognition, so that it should automatically recognize popular activities like running or biking, one of which you can set as swimming.

Again, this isn’t foolproof and isn’t designed for high-performance. I’ve had mixed results with its swim recognition; it got the appropriate amount of time I swam but only recorded one-third of the distance I actually covered.

There are also a number of designer bands and accessories coming out in the next month from Vera Wang and New York designer Public School. You’ll be able to wear your Flex 2 out for the night and continue tracking all your activity. Honestly, if I didn’t tell you the new bracelets and necklace were from Fitbit, you probably wouldn’t notice. With gold, silver, or bronze options, they look like jewelry and are just as accurate as the standard bands.

Fitbit Adventures

In the next month Fitbit is also releasing a remodeled app, which will include Fitbit Adventures. Currently, you can join challenges or see how you stack up on leaderboards in the Fitbit app, which often correlate to higher activity levels. But Adventures will be a self-driven challenge to motivate people to exercise more.

The first of these will guide you down three trails in Yosemite. These are actual trails in the park and renown outdoor photographer Chris Burkard has shot photos that will pop up on your phone screen as you hit the correlated spots as you walk or run. You can stop and scroll around the pictures, as if you’re on the actual trail in Yosemite, and you’ll be guided with information and tips. Be careful, though, if you’re looking at your screen as you go. Don’t run off a cliff.

Another “Adventure” with the New York Road Runners will allow users to experience the New York City Marathon as they run, see the crowds and the boroughs, and experience the race. It’s a way to run the marathon without winning the lottery. Or train for the race if you did get an entry.