The effectiveness of an exercise training program for 52 adults with Down syndrome (M age = 39.4 years) was evaluated. The training program consisted of cardiovascular (30 minutes) and strength exercise (15 minutes) for 12 weeks, 3 days a week for 45-minutes per session. Compared to control subjects, the training group improved significantly in cardiovascular fitness and muscular strength and endurance and had a slight but significant reduction in body weight. Greater effort must be made to promote increases in physical activity participation among persons with Down syndrome and developmental disabilities in order to reduce the potential health risks associated with low fitness and sedentary behavior.
Despite growing evidence that persons with higher levels of physical fitness have a reduced risk of various chronic conditions (i.e., Type 2 diabetes, stroke, coronary heart disease) and are more physically independent in later life (Brandon, Boyette, Gaasch, & Lloyd, 2000; Brill, Macera, Davis, Blair, & Gordon, 2000; Caruso, Silliman, Demissie, Greenfield, & Wagner, 2000), adults with Down syndrome continue to engage in high rates of sedentary behavior (Hoge & Dattilo, 1995) and have extremely low levels of physical fitness (Fernhall & Pitetti, 2001; Fernhall, Tymeson, Millar, & Burkett, 1989; Fernhall et al., 1996; Graham & Reid, 2000; Pitetti, Climstein, Campbell, Barrett, & Jackson, 1992; Pitetti, Fernandez, Stafford, & Stubbs, 1988; Rimmer, 2000; Rimmer, Braddock, & Marks, 1995). This increases the likelihood that as persons with Down syndrome age, they will have greater difficulty maintaining their ability to work, recreate, and perform self-care activities (Graham & Reid, 2000; Special Olympics Report, 2001).
Two major reports have recently been published that call attention to the growing health problems among persons with mental retardation, including Down syndrome. In March 2001, the Special Olympics Report, commissioned by a United States Senate Subcommittee, emphasized the need to establish more community-based health promotion programs for persons with mental retardation to offset the increasingly poor health status observed in this population. In December 2001, the former Surgeon General, David Satcher, convened an expert panel to discuss ways to improve health and well-being among persons with mental retardation. The published proceedings emphasized the growing problem of physical inactivity and obesity among persons with mental retardation and recommended that professionals begin to target this population in various health promotion initiatives, including higher participation in physical activity (U. S. Department of Health, 2002). Both of these reports come over a decade after Pitetti and Campbell (1991) highlighted the poor health status of persons with mental retardation and Down syndrome and referred to them as a population at risk.
To date, only two prospective training studies have been reported in the literature on persons with Down syndrome. Millar, Fernall, and Burkett (1993) conducted a 10-week walk–jog training program with 14 adolescents who had Down syndrome and reported no changes in peak oxygen uptake, the gold standard for cardiovascular fitness. Varela, Sardinha, and Pitetti (2001) also reported no significant changes in peak oxygen uptake before and after a 16-week rowing program in 16 young males with Down syndrome. These studies have led researchers to speculate that there may be some physiological limitation to improving aerobic function in persons with Down syndrome (Fernhall & Pitetti, 2001; Fernhall et al., 1996). However, these studies involved only young adults with Down syndrome, the sample sizes were small, and there was no power reported in either study (Millar et al., M age of sample = 17.7 years; Varela et al., M age of sample = 22.0 years). To date, there are no data available on an exercise intervention involving a substantially larger sample of older adults with Down syndrome. To better understand the potential training adaptations in this population, we conducted a clinical trial to evaluate the effects of a combined program of strength and cardiovascular conditioning in a cohort of adults with Down syndrome. Both of these components of physical fitness are extremely important for maintaining optimal cardiovascular health and sufficient musculoskeletal function to conduct various tasks with less physiologic stress (American College of Sports Medicine, 2000).
The study was conducted at a major university and approved by the Institutional Review Board at this university. The target population consisted of residents who lived with family members or resided in group homes and other supported living facilities in a large metropolitan area and surrounding suburbs. Eligibility criteria included the following: (a) age 30 to 70 years, (b) diagnosis of Down syndrome, (c) sedentary for the past year or longer, (d) reside within a one-hour commute of the intervention site, (e) written permission from primary care physician, and (f) able to understand instructions and complete all physiological testing (i.e., peak VO2).
A list of participant group homes and names of participants who had Down syndrome and were residing with family members were collected by a recruitment coordinator. The role of this coordinator was to identify possible participants for the study, administer a telephone screening instrument to the primary caregiver or staff director at the group home or facility where the participants resided, and arrange transportation, when necessary, for the participant to come to the fitness facility for a prescreening visit. During this phone call, the caregiver or staff director was informed that their son/daughter/resident would be randomly selected to be in the control or exercise group, and if they were chosen for the control group, they would not receive the exercise program. Once randomization was completed, participants were called back and informed of their designated group.
Project staff called participants to explain the general aspects of the study and to arrange transportation to the facility for their informed consent and screening visits. During the first screening visit, the guardian signed an informed consent document and the participant signed an assent document, which was modified to make the study easier to understand. After signing the consent document, the participant had the following measures taken: fasting blood draw, resting ECG, resting heart rate, resting blood pressure (standing, seated, supine), and basal temperature. In order to be approved for peak VO2 testing, participants' blood (e.g., CBC, chem-12) and urine (e.g., protein, ketones) tests had to be within the normal range according to standard values used for these measures.
Exercise Testing and Measurements
Prior to performing peak VO2, strength, and body composition assessments, participants came to the human performance laboratory three to four times and practiced riding a stationary cycle using the mouthpiece and noseclip. Participants pedaled the bicycle for approximately 5 minutes at their own pace, with gradually increasing resistance to assimilate the testing protocol. If a participant was having difficulty with the mouthpiece or noseclip or was not able to pedal continuously, they attended a second and occasionally third familiarization session to practice the same procedure. Blood pressure was also taken by a staff member to give participants the feeling of how this would occur during testing. Several of the participants used a child-size mouthpiece because it resulted in a better seal and felt more comfortable.
Participants were also given the opportunity to practice using the strength-testing equipment during the familiarization sessions. Approximately 30 minutes were spent demonstrating the correct use and technique of the four different strength machines. Each participant performed one to two sets of 8 to 10 repetitions on each machine. The familiarization sessions were helpful in teaching participants the correct procedures and identifying close approximations of their one repetition maximum.
Peak oxygen uptake (cardiovascular fitness)
A symptom-limited graded exercise test (peak VO2) was performed on an electronically braked upright stationary cycle (SensorMedics Ergo-Metrics 800s, Yorba Linda, CA). Peak VO2 was assessed with a SensorMedics 2900 Metabolic Cart (Yorba Linda, CA) under the supervision of a physician and exercise physiologist. The machine was calibrated before each test with standard gases. Heart rate was monitored continuously with a Marquette Max-1 12-Lead ECG machine (Milwaukee, WI). All tests were conducted with a workload controlled by the metabolic cart. A ramp cycle ergometer testing protocol was used, which allowed participants to begin cycling at a workload of 20 watts (W) and increased by 10 W every minute until maximal effort was achieved. Participants were instructed to pedal at 60 revolutions per minute (rm−1). Heart rate and blood pressure were recorded every 2 minutes. Tests were terminated if one or more of the following criteria was observed: (a) respiratory exchange ratio (RER) of 1.1 or higher, (b) plateau in peak VO2 and/or heart rate, (c) participant fatigue demonstrated by an inability to keep pedaling above 35 rm−1 (minimum speed required to maintain a constant workload and/or increase it into the next stage), and (d) abnormal blood pressure response or ECG reading. All peak VO2 data met criteria a, b, or both. None of the participants met criteria c or d.
We assessed strength using the LifeFitness (Franklin Park, IL) bench press and seated leg press machines. The participants performed a 1-RM on each machine using the procedures outlined by the American College of Sports Medicine (2000, pp. 81–82). Prior to being tested, participants were reminded of the proper lifting technique that they learned during the familiarization sessions. Strength assessment was conducted on separate days from the peak VO2 tests. Handgrip strength was measured with a Grip-A handgrip dynamometer (Tokyo, Japan). Participants were allowed three attempts with each hand, and the best score was recorded. Verbal encouragement was provided during all testing sessions.
Height, weight, and skinfold measures were recorded by a trained tester using the procedures of Lohman, Roche, and Martorell (1991). Skinfold measurements were taken with a Harpenden skinfold caliper (West Sussex, England) at the chest, abdomen, and thigh locations for men and triceps, suprailiac, and thigh locations for women. The sum of the three measures was used as the actual score. Overweight and obesity was determined from the Body Mass Index (BMI), the criteria established by the Expert Panel on the Identification, Evaluation, and Treatment of Overweight in Adults (1998).
Exercise training program
Four 12-week exercise sessions were conducted with 7 to 8 participants in each iteration. The exercise classes were supervised by a full-time registered clinical exercise physiologist and two assistants. The exercise intervention consisted of 30 to 45 minutes of cardiovascular exercise and 15 to 20 minutes of muscular strength and endurance. The first few minutes (3 to 5) of cardiovascular exercise was used as a light warmup and the last (3 to 5) were used as a cool down. During the first 2 weeks of the program, participants were taught how to use the equipment safely (i.e., getting on and off the machine) and were instructed on how to let the staff know when they were experiencing any unusual symptoms (i.e., chest hurts, dizziness). Participants exercised for 15 to 20 minutes in their prescribed target heart rate zone. During Weeks 3 and 4, emphasis was placed on reaching and maintaining their prescribed training levels for 20 to 30 minutes on one or more of the following machines: recumbent stepper, stationary cycle (recumbent and upright), treadmill, and elliptical cross-trainer. Participants selected their own equipment. By Week 5, all participants were exercising for 30 minutes in their designated training zone (50% to 70% peak VO2). Polar Vantage XL heart watch monitors (Port Washington, NY) were programmed for each participant (upper and lower training heart rate) to assure that they were exercising in the appropriate target heart rate zone. Each staff member was responsible for 1 to 3 participants to assure that they maintained their heart rate in the appropriate training zone.
Strength training was initiated at 70% of the participants' 1-RM for one set of 10 to 20 repetitions. When participants were able to complete 20 repetitions for two consecutive sessions with proper lifting technique (i.e., proper biomechanical motion; avoidance of Valsalva maneuver, which involves holding the breath), the weight was increased by 10% of their 1-RM. Participants trained on the following: LifeFitness (Franklin Park, IL) equipment: bench press, seated leg press, seated leg curl, triceps push-down, seated shoulder press, seated row, lat pull-down, and biceps curl. Blood pressure was recorded at the completion of each set.
Research Design and Statistical Methods
In the present study we employed a pretest–posttest control group design. A series of analyses of covariance (ANCOVAs) was performed to compare treatment and control group participants on fitness outcome measures, using the pretest score as a covariate. Because the number of participants in the treatment and control groups was unequal, we employed Type III sums of squares as adjusted measures. The statistical package used to perform these analyses was SAS version 8.2 (SAS Inc., Gary, NC).
The sample size was selected based on an alpha level of .05 and a minimal desired power of .80. A simulation model was created using the PASS 2000 statistical package (Kaysville, UT) to determine whether adequate power could be maintained to detect a 5% to 10% mean difference between treatment and control groups on the dependent measures. The simulation revealed that this difference could be detected with adequate power using a sample size of 20 participants per group. With participants of 30 and 22 in treatment and control groups, respectively, there was sufficient statistical power to detect small effect sizes between the two groups.
Sample demographics are presented in Table 1. As can be seen from the table, the participants were culturally diverse. Sixty-nine percent of the participants were obese (BMI over 30), and an additional 17% percent were overweight (BMI over 25). There were no significant differences in gender, ethnicity, height, weight, or age between treatment and control groups.
Four participants were diagnosed as having potential structural heart disease. Two participants had mild aortic stenosis, 1 had mild aortic stenosis plus mitral valve prolapse, and 1 had mitral valve prolapse. The participants' medical chart indicated that they all had an echocardiogram (ECG) and were subsequently approved for exercise by their primary care physician. There were no unusual ECG symptoms exhibited during the exercise testing.
Table 2 presents means and standard deviations (SDs) for pre- and postexercise outcomes by designated group along with the source and F tests for each outcome measure. The ANCOVA revealed a significant group effect on cardiovascular, strength, and body composition outcomes. When the pretest scores were controlled, the analysis showed that the exercise program had a significant effect on cardiovascular fitness and upper and lower body strength.
Compared to control subjects, treatment group participants evidenced significant gains in cardiovascular function. Significant group differences were observed for the following outcome measures: peak VO2.ml.min−1: F(1, 37) = 17.84, p <. 01; peak VO2.ml.kg−1.min−1: F(1, 37) = 16.72, p < .01; peak heartrate: F(1, 37) = 8.79, p < .01; time to exhaustion: F(1, 39) = 7.06, p < .05; and maximum workload: F(1, 39) = 15.21, p < .01. No significant difference was found in respiratory exchange ratio.
Significant group differences were observed for bench press: F(1, 44) = 21.73, p < .0001, and leg press: F(1, 44) = 27.33, p < .0001. Group differences on grip strength (left and right side) were not significant.
A significant difference between treatment and control groups was found on body weight, F(1, 44) = 7.96, p < .01. No significant differences were observed with respect to BMI or total skinfold score.
Overall, the training group improved in all outcome measures for cardiovascular fitness, strength, and body composition, whereas the control group showed no change or a slight improvement or decline (Figure 1). In general, the training group showed the greatest gains in upper and lower body strength, followed by cardiovascular fitness (peak VO2, time to exhaustion, workload). Improvements in cardiovascular fitness ranged from 14.1% in peak VO2 to an increase of 27.1% in max workload. Improvements in strength ranged from 39% to 43% on both lower and upper body strength, respectively. The training program also had a small but significant effect on reducing body weight.
To our knowledge, this is the first study to demonstrate significant gains in cardiovascular fitness and muscular strength and endurance in a controlled trial involving a large sample of adults with Down syndrome. These findings are particularly noteworthy given the relatively short-term nature of the study (12 weeks). It is plausible that a longer intervention might have resulted in even greater gains in physical fitness.
Three previous training studies conducted on adolescents and adults with Down syndrome reported conflicting findings. Millar et al. (1993) developed a training program for 14 adolescents with Down syndrome (10 experimental, 4 control). The training regimen consisted of 10 minutes of warmup activities, 30 minutes of continuous brisk walking and jogging, and a 5- to 10-minute cool down, 3 times per week for 10 weeks. Investigators reported no change in peak VO2 between the training and control group, although participants in the experimental group did attain an increased work performance, as evidenced by improvements in treadmill time. The authors concluded that a standard walking program for adolescents with Down syndrome did not increase peak VO2 as would have been expected after this type of training regimen but that improvements in endurance and physical work capacity can be attained without increases in peak VO2.
Varela et al. (2001) developed a training program for 16 young male adults with Down syndrome (M age = 21.4 years). Participants were randomly assigned to an exercise or control group (n = 8 in each group). The control group did not participate in any type of physical training. The exercise group was involved in a 16-week, 3-day per week training program using a rowing machine. Participants exercised at 55% to 70% of their peak VO2, as determined by a graded exercise test using a rowing ergometer. Results of the study were similar to those of Millar et al. (1993). Improvements in peak VO2 were not attained, despite obtaining increases in work performance (i.e., time on graded exercise test, distance covered, work level attained). Balic, Mateos, Blasco, and Fernhall (2000), however, did find significant differences in the physical fitness levels between physically active and sedentary adults with Down syndrome. However, this was a cross-sectional study with intact groups, and the investigators cautioned about interpreting the findings because of the possibility of sample bias and contamination by preexisting conditions. It is plausible that improvements in cardiovascular fitness demonstrated in this study may have been due to the very low baseline values. Greater improvements in cardiovascular fitness are generally attained by individuals who are in the lowest category of fitness (American College, 2000).
Although we were able to significantly improve the cardiovascular fitness levels in our cohort, we note that our study differs from other published studies in that we added a muscular strength/endurance conditioning component to the cardiovascular training program. In a cross-sectional study, Pitetti and Boneh (1995) found significant positive relationships between VO2 peak and leg strength, with the strongest relationship for subjects with Down syndrome. The authors suggested that leg strength may be an important contributor to VO2 peak in persons with mental retardation. Although it was not our intent to establish an association between increases in peak VO2 and increases in leg strength, from a strictly observational standpoint, participants with greater leg strength had higher peak VO2 values. In future research this relationship should be explored and the magnitude of change in peak VO2 determined that can be attained through a strength training program alone compared to a combined program of strength and cardiovascular conditioning.
One of the limitations in this study was the use of a stationary cycle to assess cardiorespiratory fitness. Fernhall (2003) noted that standard cycle ergometer protocols have not been validated in this population. We used the cycle ergometer in place of the treadmill because of the lower risk of injury (i.e., falling). Our participants were significantly older (M age = 39.4 years, SD = 6.4, range = 28 to 55) than were those in previous studies conducted with this population, and we felt it was important to ensure the safety of the participants and reduce the risk and fear of falling. We also discovered during our familiarization sessions that several of the older participants refused or had difficulty walking on the treadmill and were more comfortable using the stationary cycle. The fact that the majority of our participants attained physiological endpoints during the peak VO2 testing (i.e., RER ≥ than 1.15) is a good indication that the cycle ergometer protocol is an effective method for measuring cardiovascular performance in most individuals with Down syndrome, provided that there is a familiarization period prior to testing. However, more research is needed to confirm our findings.
Physical fitness is a strong indicator of health and is associated with a lower risk of chronic conditions, that is, cardiovascular disease, Type 2 diabetes, stroke (U.S. Department of Health, 1999, 2000), and a higher level of functional independence (Binder et al., 1999; Brill et al., 2000; Morey, Pieper, & Coroni-Huntley, 1998). Graham and Reid (2000) recently found that over a 13-year period, adults with developmental disabilities had a significant decline in physical fitness and that this decline was greater than in the general nondisabled population. This finding raises serious concern that as adults with Down syndrome age, they will be more susceptible to a premature and significant decline in function and may be predisposed to a higher incidence of cardiovascular disease and other health complications.
The performance scores of our cohort were substantially lower than those of persons of the same age and gender and among persons with mental retardation who did not have Down syndrome (Fernhall et al., 1996). The mean peak VO2 level found in our cohort prior to training was similar to women more than twice their age (Binder et al., 1999). The lower peak VO2 values reported in our study compared to previously published work on persons with Down syndrome is likely to have occurred for three reasons. First, our participants were substantially older (M age = 39.4 years, SD = 6.36, range = 28 to 55) than previous work completed with this population (Millar et al., 1993: M age = 17.0 years [control], 18.4 years [experimental]; Varela et al., 2001: M age = 21.4 years; Balic et al., 2000: age range 18 to 29 years; Fernhall et al., 1996: males with Down syndrome M age = 26.7 years; females with Down syndrome, 31.7). Considering that individuals with Down syndrome appear to have an earlier onset of aging-related symptoms, such as Alzheimer's disease and osteoporosis (Center, Beange, & McElduff, 1998; Kapell et al., 2000), it is plausible that adults in their late 30s and early 40s may have similar physical profiles to older adults without disabilities who are 20 or more years older. This is an extremely fertile area for future research given that the rate of decline in peak VO2 has never been examined cross-sectionally in persons with Down syndrome.
Second, the test modality that we used (stationary cycle) elicits lower peak VO2 values compared to treadmill testing in the range of 5% to 25% (American College, 2000). We were unable to use the treadmill with our cohort because a few of the participants refused to walk on the treadmill, and some of the older participants presented too high a risk because of poor balance and coordination.
Third, our cohort was substantially heavier than samples in previous studies with this population. Fernhall et al. (1996) reported mean body weight values in a subsample of adults with Down syndrome of 72.7 kg for men and 63.6 kg for women (combined, 68.2 kg). The combined mean body weight for our sample was 78.7 kg, approximately 10 kg higher than subjects in Fernhall et al.'s investigation. The higher body weight may have had a limiting factor on the performance of our participants.
Whether the compromised cardiovascular fitness levels observed in an older cohort of persons with Down syndrome can be alleviated with an intensive long-term training program awaits further research. Because individuals with Down syndrome are more susceptible to various health problems, including a higher incidence of cardiovascular morbidity and mortality (Marino & Pueschel, 1996), enhancing their cardiovascular fitness is a necessary and urgent health promotion strategy (Pitetti, Rimmer, & Fernhall, 1993).
Participants increased in both upper and lower body strength by 43% and 39%, respectively. These strength gains are impressive given that the training duration and frequency were modest (15 to 20 minutes per session, 3 sessions per week). In training studies with adults who have mental retardation, including Down syndrome, involving a longer duration (45 to 60 minutes) and frequency (3 to 5 days per week), researchers have reported relatively higher gains in strength (Rimmer & Kelly, 1991; Suomi, 1998; Suomi, Surburg, & Lecius, 1995). It is plausible that improvements in muscular strength and endurance in older individuals with Down syndrome may postpone premature functional decline (i.e., climbing stairs, lifting objects, carrying groceries) and may have an important effect on maintaining functional independence. Future research should be conducted to explore the relationship between improvements in muscular strength and endurance and functional performance in older persons with Down syndrome.
This work was supported, in part, by the Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities, Division of Human Development and Disability, Grant R04CCR514155; the National Institute on Disability and Rehabilitation Research, RRTC on Aging with Developmental Disabilities, Grant H133B980046; and the National Institute on Aging, Midwest Roybal Center for Health Maintenance, Grant P50 AG 15890. Fitness equipment was provided by LifeFitness, Inc., Franklin Park, IL. We thank Kelly Hsieh, Francis Gando, Donald Smith, and Todd Creviston, who assisted in the implementation of the exercise training program; and Joanne Lee, Beth Marks, Sarah Ailey, and Allison Brown for their assistance with recruitment, scheduling, and consenting participants. Requests for reprints should be sent to James H. Rimmer, Center on Health Promotion Research for Persons With Disabilities, Department of Disability and Human Development, University of Illinois at Chicago, 1640 W. Roosevelt Rd., Chicago, IL 60608–6904. firstname.lastname@example.org.