Center Of Pressure Better Approximates Body Center Of Mass Movement Than Either The Thorax Or Pelvis During Firm Surface Balance Error Scoring System Testing.

Abstract

Recently, mobile devices held/secured to the thorax or pelvis have been explored as methods to add sensitivity to the Balance Error Scoring System (BESS) during concussion evaluations. The validity of using movement of these locations to estimate sway during the BESS stances remains unknown. PURPOSE: To determine differences and relationships in postural sway estimated from movement of the pelvis, thorax, and center of pressure (CP) to total body center of mass (TBCM) movement during firm surface double leg (DL), single leg (SL), and tandem (TA) stances. METHODS: Sixteen healthy, young adults (9 men, 7 women, 21.2±2.1yrs) performed three DL, SL, and TA trials according to the BESS protocol, while kinematics of 13 body segments and CP data were concurrently recorded. Kinematic data were subsequently used to determine the TBCM, superior thorax, and pelvis locations during each trial. The root mean square (RMS) of the three kinematic and CP locations during time periods void of compensatory events were computed for each trial. Two factor analysis of variance (measure by stance) and correlational analysis of each measure with TBCM were conducted on the average across the three trials. RESULTS: Post hoc comparisons of a significant interaction (P<.001) demonstrated thorax RMS as significantly higher than TBCM during DL (P=.049, d=.83) and TA (P=.031, d=.81) stances, and significantly higher than all other measures during SL stance (P=.001 - .004, d=1.63 - 1.83). The pelvis was significantly higher than TBCM during TA (P=.002 d=1.08). While all relationships with TBCM RMS were statistically significant (P<.05), the strongest relationships existed for CP (r=.897 to.969), while the weakest existed for thorax (r=.683 - .891). CONCLUSIONS: Forceplate derived CP best approximated TBCM movement during each firm surface stance. The significantly higher values and weaker relationships with TBCM suggest the thorax may not be an optimal mobile device location for enhancing BESS testing. Future research will consider the three BESS stances on foam surfaces.