To be competitive in endurance sports, athletes must maintain intense exercise schedules. The extensive training programs that you get with MTNRDY demand high energy and nutrient intakes. These energy needs are measured in the units we know, and maybe dread: the calorie, defined as amount of energy needed to raise the temperature of 1 gram of water 1 °C. This seems like a simple definition for something so complex. So, how do we know how much energy we need?