Visual and non-visual control of landing movements in humans

The role of vision in controlling leg muscle activation in landing from a d rop was investigated. Subjects (n = 8) performed 10 drops from four heights (0.2, 0.4, 0.6 and 0.8 in) with and without vision. Drop height was mainta ined constant throughout each block of trials to allow adaptation. The aim of the study was to assess the extent to which proprioceptive and vestibula r information could substitute for the lack of vision in adapting landing m ovements to different heights. 2. At the final stages of the movement, subjects experienced similar peak c entre of body mass (CM) displacements and joint rotations, regardless of th e availability of vision. This implies that subjects were able to adapt the control of landing to different heights. The amplitude and timing of elect romyographic signals from the leg muscles scaled to drop height in a simila r fashion with and without vision. 3. However, variables measured throughout the execution of the movement ind icated important differences. Without vision, landings were characterised b y 10% larger ground reaction forces, 10% smaller knee joint rotations, diff erent time lags between peak joint rotations, and more variable ground reac tion forces and times to peak CM displacement. 4. We conclude that non-visual sensory information (a) could not fully comp ensate for the lack of continuous visual feedback and (b) this non-visual i nformation was used to reorganise the motor output. These results suggest t hat vision is important for the ver accurate timing of muscle activity onse t and the kinematics of landing.