Endurance athletes often have to snack in the midst of a workout to provide their body with enough fuel to perform at optimum levels (and to prevent their body from eating into muscle stores). But the lower the volume of food taken in during an intense workout, the better so that less energy needs to be diverted to digestion.
Dates are almost completely made of glucose, a simple carbohydrate that is easily burned by the muscles as fuel. In fact, dates have the highest glucose-to-volume ratio of any fruit, and so they make the perfect base for a snack that can be eaten before and during an intense cycling workout. In fact, the base of many natural energy bars includes dates for this reason.