Perched on a tiny ledge, 13,100ft above sea level, sits Kroger’s Canteen, an aid station part way through the Hard Rock 100 in Colorado.

When you think of aid stations, you might think of trestle tables, cups, fluid and perhaps food. But in the Hard Rock 100, a 100 mile ultra marathon through Southern Colorado’s San Juan Range in the United States, the volunteers face an endurance challenge just to get to the aid station they man.

The aid station crew only take what they can carry on their backs, and given the limited space on the mountain ledge, there’s only enough room for just seven volunteers.