Influence of motor instruction words on body movements in step-over motions

[Purpose] To quantitatively analyze the characteristics of movements evoked by certain motor instruction words on the basis of measurements of ankle elevation and related body movements in step-over motion tasks. [Participants and Methods] Sixty-one healthy adult participants were presented with motor instructions and asked to step over an obstacle in accordance with the instructions. The motor instructions were as follows: "Raise your XX (body part) up YY (expression)" in four combinations using "thigh" and "knee" for body part and "high" and "firmly" for expression. Using Kinect to analyze movements, ankle elevation, trunk-anteversion angle, hip-flexion angle, and knee-flexion angle were measured and statistically processed. [Results] With respect to body part, there was no significant difference in the mean and standard deviation (individual variation) values for ankle elevation. With respect to expression, hip joint and knee joint were bent significantly more for "high" than for "firmly", and although the mean value for ankle elevation was high, ankle elevation standard deviation (individual variation) values were significantly lower for "firmly" than for "high". [Conclusion] Explicit motor instruction words such as "high" may be effective in improving performance, while ambiguous motor instruction words like "firmly" may be effective in stabilizing movements.