Individuals with Down Syndrome, especially as they age, tend to be characterized with obesity, health-related problems from that obesity, poor fitness, a reduced physical work capacity, as well as hyperflexibility and low muscle tone. In the latest issue of Exercise and Sport Sciences Reviews, Fernhall et al discuss the cardio-vascular impacts of Down Syndrome and the impact of exercise training on this.
The authors begin by discussing the low work capacity (i.e. maximal oxygen consumption) of individuals with Down Syndrome (DS):
• Individuals in their 20’s with DS have a maximal oxygen consumption equivalent to a 60-year old without DS.
• Maximal heart rates in people with DS are typically 25-30 beats/minute below that of people without DS.
What causes these? The authors note that this is not due to congenital heart disease due to the fact that the studies examining this exclude people with congenital heart disease. Traditionally this has been thought to be due to a lack of understanding/comprehension and a lack of motivation on the part of people with DS. However, the authors report that with training individuals with DS can take a maximal oxygen test on a treadmill and produce consistent results, so understanding and motivation are not issues.
Other possibilities are a lack of physical activity or obesity. Interestingly, the authors report that while the DS population is sedentary it is not more so than the general population. Based upon the authors’ research, 8-10 hours of week of training still result in unusually low work capacities.
In the non-DS population, as we age we tend to accumulate more body mass. As this happens our work capacity declines. In the DS population, as they age they also accumulate more body mass but their work capacity remains constant. According to the authors, maximal oxygen consumption remains in the mid twenties (ml/kg/min) for people with DS between the ages of 9 and 45; whereas for the non-disabled population (on average) it changes from about 45 ml/kg/min to about 35 ml/kg/min over that same age range.
All of this combined suggests that understanding, motivation, obesity, and activity level are not the culprits of the reduced work capacity seen in individuals with DS. While this is oversimplifying the discussion somewhat, essentially the authors report that a combination of the brain’s control over heart rate and a reduced production of catecholamines (for example, epinephrine) are the likely culprits behind this reduced work capacity. In other words, due to the brain’s regulation a person with DS has a lower heart rate, which has an impact over their ability to supply oxygen to their body, which reduces their ability to perform long, strenuous exercise.
The authors report that exercise helps with this. I wrote an article a number of years ago about exercise and Down Syndrome, and at the time (and even today) there was little research on this. The good news is that exercise helps individuals with DS just like it helps individuals without DS. The challenge is that parents, siblings, caregivers, and individuals working with someone with DS need to be cognizant of these limitations because they impact motivation and require creative ways to address the fitness of a person with DS.
Fernhall, B., Mendonca, G.V., and Baynard, T. (2013). Reduced work capacity in individuals with Down Syndrome: A consequence of autonomic dysfunction? Exercise and Sport Sciences Reviews, 41(3), 138-147.