Down syndrome (DS) is a chromosomal condition that occurs in approximately 1 in 800 births worldwide, and causes impairments in physical function, including a reduced work capacity (as measured by VO2peak or aerobic capacity). Work capacity is important for activities of daily living, in order to live longer, healthier lives. Reduced work capacity stems in large part from autonomic dysfunction, which has been described in individuals with DS. Individuals with DS experience reduced sympathetic and parasympathetic control, which results in alterations in resting heart rate, blood pressure, and attenuated responses to sympathoexcitatory stimuli. Autonomic dysfunction may impair the ability to regulate blood flow and blood pressure to working muscles during exercise, which may cause a mismatch between oxygen supply and demand, further compromising the already reduced work capacity observed in individuals with DS. Utilization of a large muscle mass exercise, such as lower-limb dynamic exercise (similar to walking), requires a large shift in blood flow to match metabolic demand and allows the opportunity to evaluate blood flow regulation. Conversely, examination of the large changes in pressure in response to isometric exercise (i.e., a sustained contraction), allows for examination of the exercise pressor reflex as evoked by the isometric contraction. Thus, by comprehensively evaluating blood flow and blood pressure regulation, our work will further elucidate the mechanisms that underlay the reduced work capacity in individuals with DS. Improvement of overall work capacity for a population with reduced work capacity will guide future studies and exercise interventions aimed at helping to improve independence and quality of life, ultimately allowing individuals with DS to live longer, healthier lives.
Aim 1 (Dynamic Exercise): To examine the effects of an acute bout of dynamic leg kicking at both relative and absolute intensity workloads on femoral blood flow to both exercising and non-exercising muscle, in individuals with and without DS.
Aim 2 (Isometric Exercise): To examine the exercise pressor response to lower limb isometric exercise in individuals with and without DS.