For both pilots and wingwalkers, steep climbs and falls are often measured in G-force, or the force of gravity at Earth’s surface. Moving at excessive speeds — a biplane needs to be traveling at least 140 miles per hour to have the power to make a loop — stresses the body to the point where if a performer is dehydrated or sick, they might pass out, imperiling them in obvious ways. But a wingwalker, without the buffer of the plane’s body, is much more susceptible to excessive Gs, and a wingwalking pilot must ensure that the Gs are kept positive — or that the force is keeping them secured on the plane. Which is to say that a moment’s distraction can affect the wingwalker in dire ways that wouldn’t be deadly to a pilot.
Suzanne Cope in Buzzfeed.