Reproducibility of Dynamic Body Balance Measurement by Center of Foot Pressure Analysis Immediately after Single-Leg Hop Landing.

Dynamic balance was evaluated using the trajectory length of the center of foot pressure (COP) in the early phase from immediately after landing to the time of pastoral maintenance. Ten young volunteers with an average age of 23.8 years were asked to stand on one foot on a horizontal floor, hop forward half a step and land on one foot 10 times on each of 3 non-consecutive days. The peak of the vertical component of the floor reaction force (Fz), and the initiation time of the maximum value (tz) and COP trajectory length were measured by a force plate (AMTI, Ltd.). None of the subjects complained of any feeling of fear or loss of balance during the 3 days.The interclass correlation coefficient values of Fz and tz over the three days were 0.75 or higher. Single-leg hop for half a step as a motor task enabled safe measurement of COP trajectory length with high reproducibility. Fz reached its peak within 200 ms after landing and the COP trajectory length within 200 ms after landing accounted for approximately 50% of the total COP trajectory length at one second. Although the length differed in each subject, the interclass correlation coefficients for COP up to 100 ms and 200 ms were 0.68 and 0.80, respectively.The COP trajectory length within 200 ms after landing was considered to be useful as an objective criteria for the evaluation of dynamic balance in the early phase after landing.