Muscular Weakness and Force Variability in Individuals with Down Syndrome

Abstract

PURPOSE: To examine the association between muscular strength and force control in healthy young adults and in individuals with Down Syndrome. METHODS: Twenty-six healthy young adults and twenty-nine individuals with DS produced constant isometric force production via hand grip to 30% of their maximal voluntary contraction (MVC). In addition to determining MVC, the relative (coefficient of variation) and absolute (standard deviation) magnitude and the frequency dependent structure (i.e. power spectrum) of force variability was calculated. RESULTS: As expected the DS group was weaker than the non-DS group (130 N vs. 254 N) [F(1,53) = 44.2; p < .05]. The DS group had greater SD [F(1,53) = 28.9; p < .05] and CV [F(1,53) = 58.7; p < .05] compared to the non-DS group. Additionally, the DS group had a less broadband power spectrum [F(1,53) = 2.93; p < .05]. In order to examine if MVC differences influence group differences 1-way ANCOVAs with MVC as a covariate were performed. The DS group was still found to have greater absolute and relative variability as well as decreased broadband spectrum. However the group effect for absolute variability and broadbandedness was reduced, while it was increased for relative variability. Additionally, correlation analysis between MVC and indices of force variability was conducted. Significant correlations between MVC and CV (-.53) and MVC and broad-bandedness (-.40) were observed. CONCLUSIONS: Individual's with Down Syndrome deficit in muscular force control is partially related to deficits in muscular strength. This suggests that a shared mechanism(s) is contributing to a decreased in strength and enhanced force variability.