Abstract Turning behaviour in 107 adolescents was observed during walking and running under different temporal and biomechanical constraints. Participants ran and walked back and forth between two lines 9.5 m apart in a neutral environment. All of the turns that the participants made to change direction between the lines were videotaped. A general preference for turning leftwards was observed with the percentage being higher in the unconstrained running condition when compared to the walking condition (71% versus 59%, respectively). This intrinsic preference was easily overruled when positional constraints on the starting position were imposed. Such positional constraints did not, however, suppress the intrinsic directional bias observed during running. It is concluded that turning preference in humans is the result of a complex interaction between intrinsic preferences and externally imposed task constraints.