Kenneth H. Pitetti, Ph.D., FACSM
College of Health Professions
Wichita State University
Wichita, KS 67260-0043
|Reprinted with the permission of the author|
Down syndrome (DS) is a genetic condition due to complete or at least partial trisomy of chromosome 21 (i.e., three instead of two 21st chromosome). The disorder is the most common cause of mental retardation (MR) in the United States with a frequency of one per 700-800 live births. Down syndrome is thought to occur equally among all races and socioeconomic groups. Although advanced maternal age is the highest risk factor, 75% to 80% of infants with DS are born to women less than 35 years of age. Additionally, it has been determined that in 20% to 30% of cases the extra chromosome is of paternal origin, and the role of increasing paternal age is being investigated.
Not only is the presence of mental retardation consistent in persons with DS, but there is also a high risk for a decrease in the precision of physiological systems (cardiovascular, immune, pulmonary, neuromuscular), physiological regulation (glucose intolerance, adaptations to sensory stimuli) as well as a generalized increase in morbidity due to congenital heart disease, leukemia, retinoblastoma, pneumonia and other respiratory tract infections. All of the "abnormalities", however, have a wide range of variation for each individual with DS. For instance, the average Intelligence Quotient (IQ) for these individuals is approximately 50 (moderately retarded), but for some, values may be as high as 70 to 80 (extremely mild) or as low as 25 (severe).
There are two common conditions associated with DS that should be medically screened for before any person with DS engages in exercise or intense physical activity: atlanto-axial instability and heart defects. Atlanto-axial instability is caused by a laxity or looseness of the ligaments between C1 and C2 vertebrae, predisposing the individual for spinal trauma. Heart defects such as atrial and ventricular septal defects as well as valvular anomalies could impose limitations on cardiovascular capacities of some individuals. Although recent scientific studies report that, in fact, persons with these conditions should not be restricted in playing certain sports, it is still suggested that the decision of "participation" or "no participation" in sports should be made by medical professionals.
As is the case for most persons with mental retardation, the majority of persons with DS are only mild to moderately mentally retarded. Accordingly, if given the time to adjust to testing environment, the staff, and the time to practice test protocols or exercise procedures, persons with DS have sufficient motor skills and intellectual capacity to adequately perform these activities.
Protocols, methods, and techniques for evaluating the cardiovascular fitness, percent body fat, muscular fitness, and general exercise guidelines for persons with mental retardation, with and without DS, have been established (see ref. 5 and 6).
The results of the majority of studies that evaluated the anthropometric indices of persons with mental retardation have reported that the prevalence for obesity in this population is high, and in fact may be twice as high as their peers without mental retardation. Studies that have compared percent body fat between persons with DS and persons with mental retardation but without DS found that persons with DS have even higher levels of percent body fat than there peers without DS. Recent findings have suggested that lifestyle, specifically sedentary lifestyle along with an improper diet, may be the major etiologies for high levels of body fat within the DS population. The data to date also suggests that persons with mental retardation, with and without DS, may become severely obese later in life, which could produce limitations in employment opportunities and may have an impact on their health (see refs. 3 and 5).
Almost all studies of adults that are mentally retarded have shown that these individuals have inferior cardiovascular capacities and muscular strength compared their non-retarded peers (see refs. 3,4,5). Additionally, studies have also consistently reported low age predicted maximal heart rates by persons with mental retardation, with and without DS. Down syndrome seems to further exacerbates these findings. Studies have shown that persons with DS have even lower levels of cardiovascular capacity, muscle strength, and lower maximal/peak heart rates than their peers with mental retardation. Recent findings strongly suggest, as was the case for obesity, that the main cause of inferior fitness levels and low maximal/peak heart rates could be sedentary lifestyle.
Over the past 25 years there has been a major effort to move people with mental retardation out of institutions and into community-based residences. These community-based settings are less restrictive and give persons with mental retardation more options as to how much and what to eat as well as leisure time activity (or lack of it). This is supported by research that has demonstrated that persons with mental retardation in the institutional setting have significantly lower percent body fat than those living in a community setting. Additionally, this author has recently seen the heart rate response to intense exercise of adolescents and young adults, mildly to moderately retarded, with DS whose living environment was much more structured when compared to those living in a community-setting (this report is in review). That is, nutritional balanced meals were prepared for them and their daily routine involved a one hour activity period. These individuals displayed body morphologies indicative of an active, healthy individual (i.e., body fat normal). The heart rates of the persons with DS living in a more restrictive environment demonstrated heart rates during intense exercise that averaged approximately 25 beats per minute higher (and well within the age expectant range) than the peak heart rates reported for persons with DS living in a community setting. This latter finding may indeed indicate that low maximal heart rates are not necessarily inherent in the condition of DS.
Whether or not the level of general physical fitness can be improved by an exercise regimen or if body fat can be reduced by exercise for persons with mental retardation, with and without DS, is still unclear. Although increases in cardiovascular fitness was seen in adults with mental retardation following a 16-week exercise program using a bicycle ergometer, these individuals did not have DS (see ref. 2). The investigators for this study found that there was no significant reduction in either body weight or percent body fat for the group as a whole, although significant reductions in both weight and percent body fat was seen for the five women who participated in this study.
In an exercise study that involved adolescent and young adults with DS, no improvement in cardiovascular fitness was seen following a 10-wk walking/jogging exercise program (see ref 1). It is not known what effect the 10-wk walking/jogging program had on anthropomorphic indices of the participants because body weight and percent body fat was not reported.
Considering that the cause of obesity is unclear for the general population, it may be even more so for those with mental retardation. Although some studies suggest that sedentary lifestyle and improper diet may be the main contributors to this condition, it is still unknown what other factors, if any, may augment levels of body fat seen in persons with DS. For instance, it is generally accepted that metabolic factors play an important role in body composition. Of the metabolic factors, an individual's basal or resting metabolic rate can account for 65 to 75% of total daily caloric expenditure. Among a sedentary population, as in the case of persons with DS, resting metabolism accounts for the major fraction of daily energy expenditure. To date, there are no published data on the resting metabolic rates of persons with mental retardation with and without DS. Another possible factor could involve genetic disposition, in that perhaps the condition of Down syndrome per se contributes to obesity.
The effect that training and dietary intervention has on levels of body fat should also be studied as well as the health impact that excessive body fat has on this population.
Valid and reliable exercise test, both field and laboratory, that evaluate the cardiovascular fitness of persons with mental retardation, with and without DS, have been well documented (see ref. 5 and 6).
There have been a number of studies on the effect of physical training on individuals with mental retardation. Few, however, have used appropriate methodologies to determine if the training regimen was appropriate in improving the cardiovascular fitness of persons with mental retardation. The two main shortcomings of these studies were the failure to: 1) use valid and reliable exercise test evaluations to determine fitness before and after training; and 2) failure to specifically describe the exact type of exercise and the frequency, duration and intensity of the programs.
There are, however, two studies that did incorporate a methodology that allowed conclusive outcomes to be determined (ref. 1 and 2). Both of these studies were discussed in the obesity section. Pitetti and Tan (2) exercise adults with mental retardation, but without DS, on a Schwinn Air-Dyne ergometer for 16 wks for an average of 17 minutes per exercise, three times per week, at an intensity of 61% V O2peak. An average increase of 21% of V O2peak was seen for the subjects in this study.
The participants in the Millar et al. (ref. 1) study were young adult and adolescents with DS. The exercise group underwent a 10-wk walk/jog training program at a frequency of 3 times per week, for a duration of 30 minutes, and at an intensity of approximately 65-75% peak heart rate. Although the training program did not produce improvements in aerobic capacity (i.e., V O2peak), it did produce gains in peak exercise time (and grade). It is obvious that there is a need to identify more cardiovascular training programs for people with mental retardation and to determine if persons with DS respond differently to training compared to their peers without DS.
As with cardiovascular testing, adequate protocols that have been proven reliable for evaluating the muscular strength and endurance of persons with mental retardation, with and without DS, have been established (see ref. 5 and 6).
Strength training studies have demonstrated that individuals with mental retardation do respond in a similar manner to their peers without mental retardation in terms of strength gains. It is not known, however, if this holds true for persons with DS because these studies either did not involve persons with DS or did involve persons with DS but their results were not separated from the subjects without DS.
The nature of the strength training protocols that have been undertaken included calisthenics, stretching surgical tubing, and circuit training on weight machines (see ref. 5). Generally, these strength training regimens involved 8-14 weeks, 2-3 times weekly, using 3 sets of 8-12 repetitions. The extent to which strength gains seen by these studies were due to muscle hypertrophy, neurological factors, and/or task familiarization, have not been elucidated.
The present state of sport medicine and exercise physiology as it pertains to persons with mental retardation, with and without DS, is best described by Dr. James H. Rimmer (ref. 6) in his introduction to the chapter on mental retardation.
"The quantity of research that has been published on exercise physiology pertaining to adults with MR does not compare to the number of published studies on other special populations such as persons with diabetes, asthma, or spinal cord injury."
"It is evident from a careful review of the literature that exercise physiologist's have shown a low level of interest in studying adults who are classified as mentally retarded. This gap in research is perhaps associated with the mental deficit seen in this group, which may discourage many professionals from working with this population. Furthermore, the majority of exercise physiologists know very little about mental retardation and may perceive this group as difficult to work with. Fortunately, this attitude is slowly changing,....."
This author wishes to extend an open invitation to those researchers involved in sports medicine and exercise physiology to help quicken the change of this attitude.