A wind turbine blade extending in a longitudinal direction from a root end to a tip end and defining an aerodynamic airfoil cross-section between a leading edge and a trailing edge in a chordwise direction transverse to the longitudinal direction, the aerodynamic airfoil cross-section having an effective camber in the chordwise direction; the wind turbine blade comprising: blade body; first device for modifying the aerodynamic surface or shape of the blade, the position and/or movement of the first device relative to the blade body being controlled by a first actuation mechanism; second device for modifying the effective camber of the airfoil cross section; herein, in use, the first device modifies the aerodynamic surface or shape of the blade at a frequency up to a first maximum frequency and the second device modifies the effective camber of the airfoil cross section at a frequency up to a second maximum frequency, the second maximum frequency being higher than the first maximum frequency.