RESUMO
CONTEXT: Wearable sensors are increasingly popular in concussion research because of their objective quantification of subtle balance deficits. However, normative data and minimum detectable change values are necessary to serve as a references for diagnostic use and tracking longitudinal recovery. OBJECTIVE: Identify normative values and minimal detectable change values for instrumented static and reactive balance tests, an instrumented static Mediolateral Root Mean Square (ML RMS) sway standing balance assessment, and the instrumented, modified Push & Release (I-mP&R), respectively. DESIGN: Cross-Sectional Study. SETTING: Clinical Setting. PATIENTS OR OTHER PARTICIPANTS: Normative static ML RMS sway and I-mP&R data were collected on 377 (n=184 females) healthy National Collegiate Athletic Association Division I athletes at the beginning of their competitive seasons. Test-retest data were collected in 36 healthy control athletes based on standard recovery timelines after concussion. RESULTS: Descriptive statistics, intraclass correlation coefficients (ICC), and minimal detectable change (MDC) values were calculated for primary outcomes of mediolateral (ML) root-mean-square (RMS) sway in a static double limb-stance standing on firm ground and a foam block, and time to stability and latency from the I-mP&R in single- and dual-task conditions. RESULTS: Normative outcomes across static ML RMS sway and I-mP&R were sensitive to sex and type of footwear. ML RMS sway demonstrated moderate reliability in the firm condition (ICC=0.73; MDC=2.7cm/s2), but poor reliability in the foam condition (ICC=0.43; MDC=11.1cm/s2). Single- and dual-task time to stability from the I-mP&R exhibited good reliability (ICC=0.84 and 0.80, respectfully; MDC=0.25s, 0.59s, respectfully). Latency from the I-mP&R had poor to moderate reliability (ICC=0.38, 0.55; MDC=107ms, 105ms). CONCLUSIONS: Sex-matched references should be used for instrumented static and reactive balance assessments. Footwear may explain variability in static ML RMS sway and time to stability of the I-mP&R. Moderate-to-good reliability suggest time to stability from the I-mP&R and ML RMS static sway on firm ground can be used for longitudinal assessments.
RESUMO
Humans regularly follow curvilinear trajectories during everyday ambulation. However, globally-defined and locally-defined reference frames fall out of alignment during turning gait, which complicates spatiotemporal and biomechanical analyses. Thus, the choice of the locally-defined reference frame is an important methodological consideration. This study investigated how different definitions of reference frame change the results and interpretations of common gait measures during turning. Nine healthy adults completed two walking trials around a circular track. Kinematic data were collected via motion capture and used to calculate step length, step width, anteroposterior margin of stability, and mediolateral margin of stability using three different locally-defined reference frames: walkway-fixed, body-fixed, and trajectory-fixed. Linear-mixed effects models compared the effect of reference frame on each gait measure, and the effect of reference frame on conclusions about a known effect of turning gait - asymmetrical stepping patterns. All four gait measures differed significantly across the three reference frames. A significant interaction of reference frame and step type (i.e. inside vs outside step) on step length (p < 0.001), anteroposterior margin of stability (p < 0.001), and mediolateral margin of stability (p < 0.001) indicated conclusions about asymmetry differed based on the choice of reference frame. The choice of reference frame will change the calculated gait measures and may alter the conclusions of studies investigating turning gait. Care should be taken when comparing studies that used different reference frames, as results cannot be easily harmonized. Future studies of turning gait need to justify and detail their choice of reference frame.
