After the review of the Polar A300 last weekend and the Polar A370 in the future, I'm back again with another fitness wearable by Polar, called M400. The Polar M400 is an activity tracker and GPS running watch with Heart Rate sensor which comes with a standard micro USB cable, heart rate strap and heart rate sensor, user guide and built-in GPS.
The M400 wristband is comfortable on the wrist, even when bending and flexing the wrist for push-ups and lifting weights. The back of the M400 wristband features a stainless steel plate and a micro USB charging port to charge and sync the M400.
The stylish stainless steel buttons on the M400 GPS running watch are responsive and easy to press. The backlight is activated when pressing the top-left button (holding down this button locks/unlocks the watch). The bottom-left button pauses and stops workouts, as well as navigate back a page and connects to your phone (via Bluetooth) when holding it down to sync the M400 data to the Polar Flow App.
The Polar M400 GPS running watch is compatible with devices using Apple iOS 7 (and later) and Android (4.3 and later). The top-right button and bottom-right button are the navigational buttons; while the red button in the middle is for selecting options.

Main Screen Pages
The main two pages of the M400's main screen show time/date, progress bar, and a more detailed progress bar with percentage of daily activity achieved. The other main screen pages include:
Diary Page
Shows dates where you can check the days you registered a workout, how much activity you achieved for that day, and it shows also a recorded run. Selecting the recorded run shows even more detailed information such as distance, start time, duration, a summary of heart rate zones, number of calories burnt, percentage of fat burn of calories, average and max pace, and summary of speed zones. The speed zones monitors your speed/pace during a recorded workout with the GPS functionality.

The speed/pace zone monitoring functionality of the Polar M400 makes it such a great GPS running watch because you are able to target a specific pace to either keep your heart rate up at a certain level, or for training for a marathon run. The M400 GPS running watch will tell you where you need to be in regards to speed. You can manually change/adjust this to suit your needs through the settings. The last screen on the Diary page shows a summary of lap times that you can compare if you do switch a lap.
Settings Page
On this page, you can customize your sports profiles, set up an alarm for an audio beep to go off, as well as change the watch face. From the M400 settings page you can also customize specific heart rate and speed zones for each activity your perform, which is great if you are training to run a marathon race.

Fitness Test Page
The M400 will measure your cardiovascular fitness at rest based on the data you enter such as age, date of birth, height and weight to test how well your body transports oxygen through the body (VO2 Max). Once the fitness test is completed you are given a result from very low to elite as well as an estimated VO2 max.

Timers
The Timers page is another great M400 feature which is useful to improve your own pace. You can select an Interval Timer where you can set up two countdowns that can be either time-based or distance-based.
Getting Started
Before using the Polar M400, you will want to visit https://flow.polar.com/start to download the Polar FlowSync to your Windows PC or MAC and Android (4.3 and later) or Apple (iOS7 and later) device to sync your M400 with the Polar Flow web service. Follow the prompts to create an account and then download the Flow App from the App Store or from Google Play to your device . Once the Polar Flow App is installed on your device, you can pair it with your M400 watch.
Recording a Workout
To start a workout, you simply press the red button to select from the preset activities which include running, cycling, other outdoor, other indoor and mountain biking. As you select a workout the M400 starts looking for a GPS signal and also show the beats per minute if you have the heart rate sensor strapped to your chest.

Once the GPS signal reaches 100% you can start recording the activity and see at a glance on the screen a "real time pace", an "average pace" and "distance traveled". Navigating through the screens is easily done by pressing the bottom-right button. Press this button to show the time you started and how long you are on your current lap (if you want to count your lap times or do split laps, press the red button once). Press it again to navigate to the next screen page to see "altitude changes", and again to show the screen page with details of how long you were in each heart rate zone. Press this button again to see real time heart rate information, and press it one last time to show the distance, pace, lap time and real time heart rate.
Polar Flow App
The Flow App shows a 24 hour day (from midday to midnight) activity wheel which automatically records and illustrates with corresponding colors how long you lay down, sit down, stand up, walk and run, as well as inactivity periods and recorded workouts (shown with a heart symbol). On the main screen of the Flow App, you will also see a daily progress, daily goal suggestions, active time, sleep quality and weight (you can change this manually from here).
You can find further details on your recorded workouts by simply pressing each heart symbol to see the running index, distance, calories and heart rate chart that shows your BPM (beats per minute). The calendar feature is also very useful as it allows you to compare dates to see if you are improving over time.

The Verdict
The Polar M400 activity tracker and GPS running watch has a lot of useful and well thought out fitness focused features that will help you with distance and pace training, as well as heart rate training. The Polar M400 will also vibrate to warn you to move when you are inactive for too long. You can take the M400 with you for a swim as it is water resistant (up to 30 meters). The M400 battery life is very good, offering up to 7 hours of continuous usage even when enabling the GPS and heart rate monitoring tracking. When only using the watch and daily activity tracking features you can get up to 30 days of battery life. Check out the Polar M400 activity tracker and GPS running watch with Heart Rate sensor. Check out the review of the new Polar Vantage M2 sports watch.