Decreasing landing forces: effect of instruction.

OBJECTIVE To examine the effects of instructions related to joint kinematics, auditory stimuli, and imagery on lowering the vertical ground reaction forces associated with landing from a jump. STUDY DESIGN Randomised controlled trial. SETTING A laboratory in an educational institution. SUBJECTS Eighty asymptomatic subjects (27 men) with a mean age of 24 years. INTERVENTION Subjects were randomly assigned to the following groups: (1) instruction (limb position instructions); (2) auditory cue (listen to impact sounds); (3) imagery (metaphorical); (4) control. Subjects were required to jump from a box 300 mm in height and land on a force plate. Measures of the ground reaction force were recorded before and after the intervention. MAIN OUTCOME MEASURE The peak vertical ground reaction force recorded at footstrike. RESULTS The peak vertical ground reaction forces in the technical instruction and auditory groups were significantly less than those of the control group. There was no significant difference between the auditory and technical instruction groups. There was no significant difference between the imagery and control groups. CONCLUSIONS When an aim of a rehabilitation programme is to minimise forces on the lower limb during landing type activities, the findings support the use of instructions related to kinematics as well as instructions that draw the patient's attention to the sound at impact.