Exploring limb symmetry index for balance across a range of functional tasks.

Abstract

Introduction: Body symmetry and functional reciprocity represent key components of normal movement (Lu & Chang 2012, Sadeghi et al 2000, Watkins 1999) making them essential components of clinical examination. To this end a limb symmetry index (LSI) of 80 – 90% of the unaffected limb has been proposed by previous authors (Daniel et al 1982, Barber et al 1990, Sapega 1990, Petschnig et al 1998). Whilst LSI has been reviewed for a large variety of potential variables, the LSI for balance remains largely unexplored. Balance is viewed as an integral part of maintaining everyday physical activity, a good quality of life and reducing health burden (Clark et al 2016). Therefore, this study aimed to determine the LSI for balance across a variety of functional tasks; whilst reviewing the use of novel yet clinically reproducible methodology. Method: A cross-sectional observational design was used. Seventeen participants (mean age 27.6±5.7 years) were recruited from the student population at Bournemouth University. Participants reported no existing injury or other balance affecting condition. Balance was measured using two devices: an instrumented wobbleboard (SMARTwobble, THETAmetrix, UK) and a sacral mounted accelerometer (Balance Sensor, THETAmetrix, UK). Participants completed a variety of tasks including forward, lateral and medial hop landing where sacral acceleration was measured for 1 second following landing. Task analysis was completed using SPSS v23, MatLab and Excel. Results: No statistically significant differences occurred between dominant and non-dominant limb for any of the assessed tasks. The absolute mean percentage difference between limbs was 4.9%±3.7% (95% CI 1.8% - 8.0%). ICC values ranged from 0.73 – 0.96 suggesting moderate to excellent test-retest reliability for accelerometry and wobbleboard. Discussion: The LSI for balance should be expected to be around 5% regardless of task. Sacral mounted accelerometry, represents a valid and reliable measurement device, for a variety of complex balance assessment tasks including hop landing. Instrumented wobbleboards may also provide a valid and reliable, clinically accessible method for measuring limb symmetry, but may not be appropriate for evaluating a variety of tasks.