Lightweight and compact the fenix 5s is the sleeker more refined model from the new fenix 5 series designed to be more but not weigh more the fenix 5s vo2 max estimator crunches data collected from the elevate wrist based heart rate monitor to help inform and improve your chosen sport performance using the high resolution ultra rugged garmin chroma display athletes and adventurers can see in real time how well and how hard they are working check your performance condition the lactate thres