Lower-extremity asymmetries and their correlations to disability in multiple sclerosis
Date
2016
Authors
Pimentel, Richard E., author
Reiser, Raoul F., II, advisor
Rudroff, Thorsten, committee member
Tracy, Brian L., committee member
Diehl, Manfred, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Maintaining balance and muscle strength are common areas of concern for individuals with multiple sclerosis (MS). Postural stability is associated with weight distribution asymmetries during quiet stance and leg strength asymmetries in people with MS. People with MS are also known to have higher levels of functional asymmetries compared to healthy people. We examined asymmetry levels in people with MS during weight distribution in quiet stance and the sit-to-stand task as well as knee extensor and flexor strength asymmetries. We also identified associations between asymmetry levels and disability level, balance ability, and physical function. Thirty-seven people (28 women) with MS completed the testing. Quiet stance trials were performed for 1 minute with each foot individually on a force platform. Maximal pace five-time sit-to-stand (5xSTS) tests were also performed with each foot on a force platform. Vertical ground reaction forces (vGRFs) were collected during all trials. Instantaneous center of pressure (COP) positions were computed during the quiet stance trials for assessment of postural stability. Muscle strength of the knee extensors and flexors were measured via maximal voluntary isometric contraction on a customized knee extension machine. Participants pushed or pulled in 3-second intervals with ~2 minute rests in between until peak forces plateaued within 10%. The less-affected side was determined by symmetry index of the sum of knee extensor and flexor strength, unless strength symmetry index was within 10%, then self-report was used. Relative symmetry index (RSI) and absolute symmetry index (ASI) were calculated for the weight distribution and strength measures between the more and less affected side. ASI was used for correlations between all variables. Repeated measures ANOVA was used to identify differences in RSI and ASI levels between average vGRFs during quiet stance and 5xSTS, peak vGRFS during 5xSTS, knee extensor and knee flexor strength. Pearson correlations were performed to examine associations. Pairwise post-hoc comparisons of the ANOVA showed that knee extensor strength asymmetries were greater than 5xSTS vGRF average and max instantaneous asymmetries in both RSI and ASI sets. The 5xSTS ASI correlated highest with the balance and disability measures. Based on these results, it appears that the expression of lower-extremity asymmetries are highly task dependent. As a result, no one test will suffice when assessing side-to-side differences in people with MS. However, if only one test is available, 5xSTS asymmetries may be more reflective of functional disability than those expressed during other tasks.