A new technique to perform in situ miniaturized bending fatigue experiments was applied to single crystal copper beams. Pronounced monotonic hardening and an increasing Bauschinger eﬀect were observed with increasing normalized displacement. Remarkably, no cyclic hardening or softening was observed. Three-dimensional discrete dislocation dynamics simulations support these results and point out the importance of dislocation pile-ups and local hardening mechanisms. These lead to local strain redistribution and the activation of new glide planes as observed experimentally.