Aerobic Capacity is Related to Muscle Strength in Individuals with Down Syndrome

Abstract

Individuals with Down syndrome (DS) have low levels of muscle strength and aerobic capacity. It has been suggested that the low level of muscle strength impacts the low aerobic capacity in persons with DS, but the relationship between muscle strength and aerobic capacity remains unclear. PURPOSE: To investigate the relationship between muscle strength and aerobic capacity in adults with DS. METHODS: Thirty-six adults (age = 27.6 + 8.1 yrs; weight = 76.1 + 15.1 kg) with DS were recruited. None of the subjects were institutionalized and all were free of cardiovascular disease or muscle problems. Subjects completed a treadmill test to exhaustion with oxygen uptake measurements using validated individualized protocols, and several test of leg muscle strength. Maximal leg extension and flexion strength were evaluated with isokinetic tests at 60 degrees/second, and isometric tests at 45, 60 and 75 degrees of extension. The relationship between aerobic capacity and muscle strength was evaluated using Pearson correlations and a stepwise multiple regression. RESULTS: Aerobic capacity was significantly (p< 01) related to isokinetic extension and flexion peak torque (r=.47 and r=.42 respectively), and to isometric peak torque for both extension and flexion at each of the positions evaluated (correlation coefficients between 0.46-0.57). The stepwise multiple regression revealed that only the peak torque during the isometric leg extension at 75 degrees and the peak torque during the isokinetic leg extension were included in the model as significant predictors of aerobic capacity, yielding the following prediction equation explaining 42% of the variance: VO2 (ml/min) = 2.982 (isometric peak torque) + 3.043 (isokinetic peak torque) + 1024 (R=0.645; p< .001). CONCLUSION: Leg muscle strength was significantly related to aerobic capacity in individuals with DS, and the relationship was higher than what has been reported for other non-disabled populations. However, only two leg extension variables were included in the final model, suggesting the leg flexion strength does not influence aerobic capacity in this population. If aerobic capacity and leg strength are causally related in this population, our data suggest that resistance training may improve aerobic capacity in individuals with DS.