According to the National Institute of Child Health and Human Development (18), Down syndrome (DS) occurs in approximately 1 in 800 newborns. The majority of individuals with DS have an extra copy of chromosome 21, which results in the individual having 47 chromosomes instead of the normal 46. There are other forms of DS (or trisomy 21) that result from an individual having part of chromosome 21 located on other chromosomes (translocation trisomy 21) or having a mixture of cells with 46 and 47 chromosomes (mosaic trisomy 21) (2,3).
Individuals with DS experience a range of general medical, endocrine, musculoskeletal, developmental, and cognitive complications. The purpose of this article is to describe the complications from DS, particularly with an emphasis on how these affect health and fitness. It will then review the literature on exercise for individuals with DS. Finally, this article will provide recommendations for developing exercise programs for people with DS.
Although the phenotypic features of DS vary from person to person, individuals with DS are more likely to experience a number of medical conditions, including, neurological, cognitive, cardiac, and orthopedic conditions. These include intellectual disability, which is always present in DS although the severity varies (19). Other medical complications include increased prevalence of Alzheimer's disease, leukemia, congenital heart disease, dementia, seizure disorders, sleep apnea, excess mobility of the atlas and axis, gastrointestinal concerns, vision and hearing problems, endocrine disorders, and musculoskeletal abnormalities (12,14,19,21,22,25). The rest of this section will cover endocrine disorders and musculoskeletal abnormalities.
Hawli et al. (12) identified several types of endocrine disorders common to DS, all of which have implication for growth and development. These include thyroid dysfunction, gonadal dysfunction, and growth disruption. Thyroid dysfunction is the most typical endocrine abnormality and primarily refers to hypothyroidism, which occurs in up to 54% of adults with DS (12). Hypothyroidism results in the diminished or absent secretion of thyroid hormone. This leads to fatigue, decreased cardiac output, reduced heart rate, reduced blood volume, and increased body weight (11). Gonadal dysfunction refers to hypogonadism, where the ovaries and testes fail to secrete hormones in adequate levels. This can lead to delayed menarche in females and can also impact male secondary sexual characteristics, such as axillary and facial hair, development of sexual organs, sperm count, and infertility (11,12). Individuals with DS may be deficient in growth hormone. This results in a reduced growth rate (compared with their peers who do not have DS) and a short stature (12).
In terms of musculoskeletal abnormalities, hypotonia and hyperflexibility are present in those with DS (12,22). Hypotonia refers to the absence of resistance to movement in muscles (11). This is linked to the control of the motor cortex over the muscles (11). Hypotonia and hyperflexibility have an impact on bone mass, muscular strength and power, gait, and motor development.
Low muscle mass combined with other factors (trouble in absorbing vitamin D and inadequate exposure to the sun due to inactivity) results in reduced bone mass compared with individuals without DS (12). Shields et al. (23) report that people with DS are at increased risk of osteoporosis.
Individuals with DS have reduced strength and power compared with individuals without DS. Croce et al. (8) studied individuals with developmental disabilities (with DS and without DS) and compared them with sedentary normal controls to see if there were differences between peak torque and power of the hamstrings and quadriceps. They found that individuals with DS had between 29 and 47% of the peak torque of the sedentary normal individuals and between 26 and 45% of the average power of the sedentary normal individuals.
In theory, hypotonia and hyperflexibility could impact an individual's ability to develop strength and power in several ways. First, hyperflexibility could result in a diminished stretch reflex. This would result in a diminished performance on activities that involve jumping, sprinting, or throwing. It also could reduce power output during activities when it is needed rapidly (e.g., when falling). Second, hyperflexibility could reduce stiffness during ground contact (and therefore force exerted against the ground) when running or walking. Third, hyperflexibility could reduce joint stiffness, making some exercises more dangerous to perform. For example, the shoulder joint might not be as stable during bench presses, overhead squats, or snatches.
Hypotonia and hyperflexibility impact gait. Gait patterns in DS are often characterized by external rotation of the hips, knees in flexion/valgus, and externally rotated tibias. In addition, the gait of children with DS is characterized by marked pronation of the feet. This may progress to gait being compromised by plantar fasciitis, fatigue, and the early onset of arthritis that is associated with flat feet in adolescents and adults (21). All these have an impact on an individual's comfort level with certain modes of exercise, such as treadmill walking or running.
Infants with DS develop motor skills in the same sequence as infants without DS, but do so at a slower pace (24). Brunamonti et al. (5) investigated the cognitive control of movement comparing patients with DS to patients with a developmental disability without DS. It was noted that those subjects with DS had a 9–15% greater reaction time than subjects without DS and had more trouble-suppressing action when a stop command was inserted into a task. The authors posit that this is due to a defective cooperation between the prefrontal cortex, basal ganglia, and the cerebellum. If true, this suggests challenges with activities involving reacting to sudden or rapidly changing stimuli.
In addition to the medical conditions associated with DS, there are secondary conditions experienced as a result of the primary disability (14,15). While studying individuals with DS, it was found that the most common secondary conditions were a higher body mass index (BMI), a lack of physical fitness and conditioning, fatigue, memory problems, and communication/reading difficulties.
WEIGHT AND FITNESS
Individuals with DS have a reduced resting metabolic rate and a higher frequency of obesity when compared with individuals without DS that puts them more at risk for cardiovascular disease and metabolic syndrome (4,14,21). In addition to decreased strength and power, individuals with DS have a drastically lower peak oxygen consumption, lower aerobic capacity, and lower peak heart rate than individuals without DS (4,22,23). These physical fitness variables will have an impact on activities of daily life (7).
Several reasons may exist for the reduced physical fitness seen in individuals with DS. First, the sympathetic and parasympathetic nervous systems may function differently in people with DS. For example, Fernhall and Otterstetter (10) noted that adults with DS have a reduced sympathetic response and reduced vagal withdrawal to cold pressor and hand grip tests when compared with individuals without DS. Second, the combination of hypotonia, hypothyroidism, hypogonadism, obesity, and motor development challenges will have an impact on the difficulty of exercise. This may make someone with DS less likely to choose to pursue an exercise program. Third, the combination of motor development challenges and the intellectual disability in individuals with DS lead to an avoidance strategy when it comes to cognitive challenges (21). This means that they are less likely to take up physical activities that they are not familiar with.
Shields et al. (22) studied the amount and intensity of physical activity of children with DS. In their study of Australian children, no child performed 20 minutes of continuous vigorous physical activity 3 times per week. Only 42% of the children studied performed at least 60 minutes of moderate-to-vigorous physical activity each day. They also found a significant inverse relationship between the level of physical activity and the age of children with DS (r = −0.67).
EXERCISE AND DOWN SYNDROME
In theory, exercise programs would be beneficial to individuals with DS. Unfortunately, research on exercise and DS is lacking, can be contradictory, and rarely provides clear-cut guidelines to practitioners (2). The remainder of this article will review the literature on exercise and DS and will provide basic recommendations for developing exercise programs.
Andriolo et al. (2) in their review noted that there is little published evidence of high quality in the area of aerobic exercise and DS. Additionally, the effectiveness of aerobic exercise training in improving the health of adults with DS remains uncertain. The scientific literature, however, conflicts with this statement. This conflict may be because of the fact that the review by Andriolo et al. (2) was based on only 3 studies.
A number of studies have examined the effects of strength training and aerobic exercise programs on individuals with DS. These studies find that exercise programs are effective at improving aerobic fitness measures and strength. Improvements in body mass and psychological variables are less clear. Table 1 summarizes these studies.
Aguiar et al. (1) studied the effects of judo on motor coordination. In their study, subjects with DS participated in 16 weeks of supervised judo instruction, 3 times per week, each session for 50 minutes. The authors used a gross motor function measure that covered 88 items organized into lying/rolling, sitting, crawling/kneeling, standing, and walking/running/jumping to evaluate motor coordination. At the end of the study, the authors found a significant improvement (P < 0.05) for performance on the gross motor function measure but do not provide a breakdown of this performance improvement.
Carmeli et al. (6) studied the effect of a training program involving pain-free low-intensity walking on elderly individuals with DS. Their subjects were divided into 2 groups, one with intermittent claudication (i.e., pain in the muscles during walking) and the other without. Subjects exercised on the treadmill for 15 weeks, 3 times per week at a speed below pain and breathless thresholds. Initially, subjects walked for 5–15 minutes and progressed to 40 minutes on the treadmill. Both groups made significant increases in the distances walked, duration on the treadmill, and speed (results reported in Table 1 average the gains from both groups).
Mendonca et al. (16) studied whether adults with DS responded differently to an exercise program than adults without DS. After 12 weeks of combined cardiovascular and strength training, both groups made similar improvements in muscular strength and peak oxygen consumption.
Based on the literature reviewed, aerobic exercise and strength training appear to yield positive benefits to aerobic fitness and muscular strength/endurance in individuals with DS. These benefits seem to be similar to those seen in populations without DS. It is unclear if exercise has a positive effect on BMI or psychological variables (9) in individuals with DS.
There are limitations to the scientific research on subjects with DS. First, it is not known whether the gains in fitness from an exercise program can be retained over time because there are no long-term studies. Second, it is not known whether age, gender, or concurrent health problems may impact exercise program outcomes. Finally, implications for long-term program effectiveness have not been studied (17).
Based on the research that has been done, the limitations mentioned above, and extrapolating from populations without DS, several recommendations can be made regarding exercise programs and individuals with DS. These recommendations deal with supervision, the inclusion of cardiovascular exercises, and the inclusion of strength training exercises.
First, this population requires supervision to ensure a successful exercise program. Dodd and Shields (9) recommended a staff to participant ratio of 1 staff for 2–4 participants. This is important to keep the individual focused, motivated, and exercising at the appropriate intensity.
Second, people with DS will benefit from a cardiovascular exercise program. A lack of balance and motor skill may have an impact on an individual's comfort with walking, jogging, or elliptical cross-trainers. Dodd and Shields (9) recommended cardiovascular exercise 3 times per week, progressively working toward an intensity level of 50–75% of peak oxygen consumption for 30 minutes.
Third, strength training is appropriate for people with DS, although it may need to be modified. Keeping in mind challenges with learning new motor skills and balance, individuals with DS should begin a strength training program using selectorized strength training equipment 2–3 times per week emphasizing the entire body. The studies that have been reviewed indicate that 1–3 sets at 12 repetition maximum (RM) per exercise are appropriate.
Should people with DS exercise with free weights? There is no research to address this topic. Based on the information presented in this article, there are some reasons to be cautious. First, it needs to be kept in mind that this population is hyperflexible. This means that there is a lack of stability to the joints, especially during explosive movements (such as the Olympic-style lifts) that could theoretically increase the risks of injury. Second, it will take this population longer to master the motor skills associated with free weights due to a combination of hypotonia, balance, and intellectual disabilities. This may become a source of frustration and may impact the participant's motivation. Third, individuals with DS are going to require more supervision using free weights than individuals without DS to keep them focused on good technique, to spot, and to provide motivation.
With the above cautions in mind, if free weights are attempted, they should be approached as part of a larger progressive program:
- Cardiovascular exercise needs to be performed in conjunction with the strength training.
- Individuals should begin strength training on selectorized equipment and progress to free weights over time as their individual comfort level allows.
- Free weight exercises should be substituted for selectorized equipment exercises “one at a time” rather than an abrupt shift in exercise modes. Once the individual is comfortable with one free weight exercise, another may be substituted.
- Two to three sessions per week with 1–3 sets at 12RM is appropriate for free weights.
- Table 2 provides a sample program incorporating the above guidelines.
Individuals with DS may benefit from a structured exercise program. It is important for health, the ability to function in daily life, the opportunity to socialize, and may help enhance self-esteem and prevent depression. Despite the benefits, there is a need for more research with this population. Because of the physiological differences, it is unclear if individuals with DS (a) will respond to exercise in a manner similar to the population without DS, (b) how exercise should be programmed over the long term for people with DS, and (c) if free weights are appropriate and how exactly they should be incorporated into the exercise program.
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