title: Complexity of force output during static exercise in individuals with Down syndrome.
abstract: Force variability is greater in individuals with Down syndrome (DS) compared with persons without DS and is similar to that seen with normal aging. The purpose of this study was to examine the structure (in both time and frequency domains) of force output variability in persons with DS to determine whether 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), and 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-to 4-Hz bandwidth than the young and older 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 amplitude of low-frequency oscillations in the force output signal than age-matched non-DS peers. Interestingly, young persons with DS and older persons without DS have similar time-dependent structure of force output variability. This would suggest a possible link between premature aging and less complex force output in persons with DS.
authors.affiliation: Department of Kinesiology and Community Health, University of Illinois at Urbana, Champaign, Champaign, Ilinois 61820, USA. kheffer2@uiuc.edu
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Heffernan
authors.forename: Jacob J
authors.initials: JJ
authors.lastname: Sosnoff
authors.forename: Edward
authors.initials: E
authors.lastname: Ofori
authors.forename: Sae Young
authors.initials: SY
authors.lastname: Jae
authors.forename: Tracy
authors.initials: T
authors.lastname: Baynard
authors.forename: Scott R
authors.initials: SR
authors.lastname: Collier
authors.forename: Stella
authors.initials: S
authors.lastname: Goulopoulou
authors.forename: Arturo
authors.initials: A
authors.lastname: Figueroa
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Woods
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Pitetti
authors.forename: Bo
authors.initials: B
authors.lastname: Fernhall
mesh_terms: D000328:Adult; D000368:Aged; D003627:Data Interpretation, Statistical; D004314:Down Syndrome / Q000503:physiopathology*; D019277:Entropy; D015444:Exercise / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D014159:Transducers; D014202:Tremor / Q000503:physiopathology; D055815:Young Adult