MEASURED VERSUS PREDICTED VERTICAL DISPLACEMENT OF THE SACRUM DURING GAIT AS A TOOL TO MEASURE BIOMECHANICAL GAIT PERFORMANCE

The vertical displacement of the sacrum during walking is proposed as an estimation of the overall biomechanical performance of walking, ind ependent of cardiopulmonary factors. Vertical sacral displacement duri ng walking was measured using an optoelectronic motion analysis system in 10 normal volunteers at variable speeds. Oxygen consumption was si multaneously measured. The actual vertical displacement of the sacrum, when correlated with body weight, reliably predicted oxygen consumpti on (r(2) = 0.91). The relationship between vertical sacral displacemen t and oxygen consumption persisted when controlling for the variables, velocity, square of velocity, cadence or stride length, each known to co-vary with cardiopulmonary performance, A mathematic model designed to predict the vertical displacement of the sacrum, based on sacral h eight and average stride length, was tested. The actual vertical sacra l displacement correlated with predicted displacement (r = 0.94). Unil ateral immobilization of each subject's knee resulted in a greater ave rage vertical sacral displacement during gait than predicted. Comparin g measured with predicted vertical sacral displacement may provide a c linically useful and specific overall assessment of biomechanical gait performance.