Monitor your body during training and recovery with a single device.

Combine a fully functional training watch with an activity monitor, and you get the Polar M400. It can track a morning interval workout before punching the clock and then remind you to come unglued from your office chair during the day. This double feature, however, comes at a cost: complexity.

GPS connectivity is excellent. The watch connects with satellites in seconds, holds a signal through moderate tree cover and reads changes in speed within seconds.

No matter how you like to monitor a workout or race, the M400 can do it. Speed and distance, both from GPS, and heart rate data are parsed many ways. Polar provides its own training software, and workout data can be ported over to popular training apps, but the process is far from seamless. Between workouts, it doubles as a fitness monitor.

With an overabundance of stats in small fonts, checking speed, HR or distance during a run is challenging and can take many clicks and too much concentration to be practical. Expect to take time learning the watch and software before putting it to use. This is the crux of the M400—it can measure just about anything, but putting that info to use can be challenging.

Takeaway: Lots of data, a little complex ($250, polar.com)

Breakdown:

What it does: Tracks speed, distance and heart rate during a workout, and estimates sleep quality and general activity between workouts.

How it’s better: It’s one device that can do just about anything. If you use a training watch and fitness monitor, this can replace both.

Why you need it: Obsessive data junkies will love the bounty of info—and high-performing GPS—from the M400. Unless you’re on a wilderness adventure, it can collect pretty much all the essential training data.