WHOOPs wrist-worn strap is a key component of its performance optimization system that helps elite athletes and teams win more. The device, which continuously measures the nuances of an athletes strain and recovery through a near-medical grade sensor, was designed to be always on so it can provide the wearer with the highest level of body awareness. The sleek strap is lightweight and includes three layers of fabric and polyurethane for performance comfort. A small modular battery pack, which is charged separately, slides along the slots on the sides of the device, just under the clasp, and will lock into place for true 24/7 functionality. The WHOOP Strap is the first on the market that users can charge either on-the-go or during a nights sleep without having to be removed. The sleek WHOOP strap marries fashion with function by collecting more than 150 MB of physical data per athlete per day by measuring five key physiological variables more than 100 times per second: heart rate, heart rate variability, skin conductivity, ambient temperature and accelerometry. This data is used by coaches and trainers to inform training and game day decisions.