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 ϭ 29, age 26 yr), and healthy young (n ϭ 26, age 27 yr) and older (n ϭ 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 Ͻ 0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls (P Ͻ 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 Ͻ 0.05). The DS group had significantly lower ApEn values than the young controls (P Ͻ 0.05), but there were no differences in ApEn between the DS group and the old controls (P Ͼ 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. motor control; approximate entropy DOWN SYNDROME (DS) is the most commonly inherited form of developmental disability in North America (7). It is estimated that 1 out of every 700 -1,000 newborns in the United States will be diagnosed with DS, and there are currently over 350,000 persons living with DS in the United States (7). In more than 90% of cases, DS results from an excess of genetic material from chromosome 21 (i.e., trisomy 21). Trisomy 21 results in a constellation of dysfunctions, spanning several physiological systems. Individuals with DS have poor balance, poor coordination, slow reaction time, reduced visual-motor control and sensory acuity, gross and fine motor skill dysfunction, and overall greater movement variability (1,2,11,29,30,60). Motor dysfunction in persons with DS prevents successful completion of many activities of daily living, attenuates vocational productivity, and contributes to low physical work capacity (20,36). This ultimately results in increased dependence on others and assisted living (36). Most striking, lack of mobility has been shown a predictor of mortality in this population (19,52). As such it is imperative to increase the understanding of the factors underlying neuromotor function in DS.The origin of moto...

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