It has been nearly three years since Polar first released the M400 running watch, and now the company is updating it. Polar announced the $229 M430 today, a new version of the previous runner's watch with slight improvements to the device's design and software that may be unnoticeable at first but should make a big difference during workouts.

The general design of the M430 is very similar to the M400—it's a bulky, rounded-square module with five physical buttons and a soft-touch silicone strap. The external features of the module haven't changed much, but Polar made the strap thinner, lighter, and more perforated to allow for better ventilation. It looks quite similar to Nike's Apple Watch Series 2 straps, with three rows of small holes covering the band. Those types of bands make it easier for the skin on your wrist to breathe and easier for sweat to escape. The module itself is 12mm thick and weighs 51 grams, and Polar claims its design combined with the improved strap will decrease pendular motion that occurs while running (those are the small movements that the M430 is subjected to every time you swing your arm during a run). If worn properly, fitness trackers don't seem to move at all while on your wrist, but they are adjusted and jostled slightly with every bit of arm movement.

The M430's accelerometer has also been improved to provide pace and distance metrics for indoor running on treadmills in addition to outdoor trail running. Most fitness trackers, and running devices in particular, only provide accurate pace and distance calculations when you're running outside, whether they have built-in GPS or not. Now all kinds of runners can use the M430 to its fullest extent no matter where they're running or what their training plan suggests.

The optical heart rate monitor on the underside of the M430 is the same six-LED device Polar has integrated into a number of its products, including the M600, but the company made changes to the algorithms that interpret the heart rate monitor's data. According to Tom Fowler, president of Polar USA, the biggest difference the new algorithms provide is improved stability. Optical heart rate monitors are notoriously unstable when measuring rapid pulse changes. Most fitness devices that use them have the same problem: they're too slow to catch up to high beats per minute or too slow to level off at low beats per minute. Polar claims that the new algorithms make the M430's heart rate monitor nearly as stable as the company's H10 chest strap during running and other similar exercises. Polar also plans to push out firmware updates to existing devices to improve their heart rate monitors with the new updated algorithms.









But the improved heart rate monitor won't be totally infallible—or exactly the same as a chest strap. The most likely scenario in which the M430's monitor could lag is during a very intense interval training workout, a tough weight-training session, or any circuit in which your heart rate spikes and dips rapidly and frequently. This is not just because of the optical heart rate monitor's method of capturing data but also because of its placement on the wrist. A chest strap is better suited for workouts like this thanks to its location close to the heart and because it's not subjected to the rhythmic movement that wrist-based monitors are.

Since the M430 is technically a multi-sport watch (you can download a selection of trackable exercises from Polar's list to the watch) and the company knows every user's training plan is different, it made the M430 compatible with its other heart rate monitoring chest straps. With that feature, you can connect Polar's H10 chest strap to the device so your heart rate data will come from both the chest strap and the watch's onboard monitor. One doesn't override the other in this scenario; they work together to capture a more complete picture of your heart rate during an intense workout.

The M430 has a 240mAh battery inside that Polar claims can last weeks on a single charge. Since it's a running watch, its true battery life will be how long it can last through workouts that include GPS. Polar estimates the watch will get up to eight hours with one-second GPS queries (meaning that the GPS is pinpointing your location every second). There's also a low-power mode on the M430 that should extend the watch's battery life to 30 hours with one-minute GPS queries. The frequency of the GPS queries won't affect the mapped route that you see at the end of a run, but it will slightly affect the type of information you can see in real time (any information that relies on GPS will refresh at a rate of between one second and one minute depending on the battery mode you're using).

Like most of Polar's other wearables, the M430 connects to Polar Flow and transfers all your activity data to that app. In addition to regular workouts, the watch tracks daily steps, calories, distance, and sleep. It delivers smartphone text and call notifications to your wrist as well, but it may not be the best all-day device, even with its slightly slimmer profile. All of Polar's programs are available on the M430, including its smart coaching feature, estimated recovery time, and the Polar Running Index, which gives you a one-number post-workout score to tell you how well you're progressing toward completing a goal. It also supports Polar's running program, which gives you specific workouts to do in order to train for a 5K, 10K, and other races. The running program doesn't just give you cardio workouts to do; it incorporates strength training and other exercises into your specially designed program, all of which are geared toward helping you run better. The $229 Polar M430 running watch is available for preorder today in orange, white, and gray, and it will ship widely in May.