At just 49g, this wristwatch has been engineered to perfection, delivering powerful tracking functionality in a small package. The tracker allows users to switch between activity modes with just the press of a button, measuring steps, calories and even fitness age. It also lets users check whether they are training at an optimal level, peaking, or overreaching. The device can also be paired with a heart rate chest strap accessory, to access more detailed metrics, such as lactate threshold and a heart rate variability stress test.