Submitted on April 25, 2008
Revised on January 6, 2009
Accepted on January 20, 2009
Complexity of force output during static exercise in individuals with Down Syndrome
Kevin S. Heffernan1*, Jacob J. Sosnoff2, Edward Ofori3, Sae Young Jae4, Tracy Baynard5, Scott R. Collier6, Stella Goulopoulou6, Arturo Figueroa7, Jeffrey A Woods5, Kenneth H. Pitetti8, and Bo Fernhall3
1 Tufts Medical Center
2 University of Illinois Chicago
3 University of Illinois Urbana-Champaign
4 University of Seoul
5 University of Illinois at Urbana-Champaign
6 Syracuse University
7 Florida State University
8 Wichita State University
* To whom correspondence should be addressed. E-mail: KHeffernan{at}TuftsMedicalCenter.org.
Force variability is greater in individuals with Down Syndrome (DS) compared to persons without DS and is similar to that seen with normal aging. This study examined the structure of force output variability in persons with DS in order to determine if deficits in force control are similar between individuals with DS and older adults. An isometric handgrip task at a constant force (30% of maximal voluntary contraction) was completed by individuals with DS (n=29, age 26 yr), and healthy young (n=26, age 27 yr) and older (n=33, age 70 yr) individuals. Mean, standard deviation (SD), coefficient of variation (CV) were used to analyze the magnitude of force output variability. Spectral analysis and approximate entropy (ApEn) were used to analyze the structure of force output variability. Mean force output for DS was lower than in young controls (p<0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls (p<0.05). The DS group had a significantly greater proportion of spectral power within the 0-4 Hz bandwidth than the young and old controls (p<0.05). The DS group had significantly lower ApEn values than the young controls (p<0.05) but there were no differences in ApEn between the DS group and the old controls (p>0.05). In conclusion, young persons with DS demonstrate enhanced temporal structure and greater low-frequency oscillations in the force output signal than age-matched non-DS peers, while exhibiting similar fndings as older persons without DS.
