Effect of continuous aerobic vs interval training on selected functional fitness parameters of adults with intellectual disability and Down syndrome
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Most individuals with intellectual disability (ID), including those with Down syndrome (DS), are overweight or obese and live a sedentary lifestyle. Non-communicable diseases such as hypertension, diabetes, high total cholesterol and metabolic syndrome have a high prevalence in this group. Individuals with an ID report poor aerobic capacity, with persons with DS reporting even poorer aerobic capacity. A poor aerobic capacity is related to poor cardiovascular fitness, a risk factor for cardiovascular disease. Persons with ID and DS are also reported to have low functional fitness capacities. Functional fitness batteries exist in the general, elderly and ID and physical disabled populations, but standardised tests involving adults with DS do not exist. Individuals with DS are therefore often pooled with ID individuals in spite of discernable functional fitness capacities. It is therefore important that a fitness battery specific for DS is developed. Structured exercise training presented limited potential to significantly ameliorate anthropometrical and cardiovascular variables in adults with ID and DS. Recently, interval training (IT) has been applied to improve health outcomes of populations at risk for chronic diseases. In this regard the significant physical, anthropometrical and metabolic benefits associated with interval training have been demonstrated in a variety of populations. The purpose of this study was to: 1) determine the test-retest reliability for a battery of test items in an adult population of DS individuals. 2) Determine the validity of two commonly used field tests (PACER and 6MWD) with the gold standard of cardiorespiratory fitness (direct VO2 max). 3) Determine the effect of structured IT versus continuous aerobic training (CAT) on various anthropometrical, health, functional and physical benefits in adults with ID and 4) DS. In the first study, forty-three adults with DS (24 men and 19 women) aged 18–50 years (from Potchefstroom, Pretoria and Brits) completed a battery of tests twice in a two-week period. The battery of tests consisted of two balance items, two flexibility items, five muscular strength and endurance items, two aerobic items, and one functional task. The test-retest relative reliability for all repeated tests was assessed with intraclass correlation coefficient performing one-way analysis of variance. The testretest absolute variability was measured by using the standard error of measurement (SEM) and reliability data was visualised with a Bland-Altman plot. In the second study, the same forty-three adults with DS randomly performed three aerobic tests on non-consecutive days during a one-week period. To assess validity, peak oxygen uptake was measured directly on a motorised treadmill. The two field tests included the 16-metre PACER and the 6MWD test. Pearson-product moment correlations were performed. A linear regression analysis was conducted to determine criterion-related validity between the field tests and the VO2 peak test. The third study included 46 persons with ID (30 men and 16 women) from Brugge, Belgium. They were matched on age, gender and IQ and distributed between IT (n=17), CAT (n=15) and control (n=14). The training groups exercised for 15 weeks, twice weekly (40 minutes). IT was performed in two blocks of 10 minutes (block 1 and 3). Participants performed 10 sprints of 15 seconds (45 seconds of relative rest) on a cycle ergometer. During block 2 continuous training was performed. The CAT group performed three blocks of 10 minutes of continuous training (cycling, walking, stepping). After eight weeks the intensity of training was increased. To evaluate prepost differences between groups, a repeated ANCOVA with post-hoc Bonferroni test was performed. Lastly, the fourth study included 42 adults with DS (25 men and 17 women) and a mean age 33.8 ± 8.6 years. Participants were randomly allocated to one of three groups (IT, CAT, control). Training was performed for 12 weeks (three times a week). The IT group performed ten-30 second all-out sprints with 90 seconds (1:3 work:rest ratio) of low cadence, low intensity cycling or walking. The CAT group performed continuous cycling and walking at an intensity of 70%–80% of VO2 peak. To evaluate pre–post differences between groups, a repeated ANCOVA with post-hoc Bonferroni test was performed. Results showed that all functional fitness tests were feasible and demonstrated excellent test-retest reliability (ICCs>0.9) and acceptable measurement precision (SEM<SD/2). The analyses indicated that there was no major systematic bias in the plots and the scatter around the Bland-Altman was distributed randomly. Linear regression revealed that the 16-metre PACER (R2=0.86) and the 6MWD (R2=0.75) were significantly related to directly measured VO2 peak (p<0.05). Both the 16-metre PACER and the 6MWD significantly correlated with VO2 peak for adults with DS. The relationship was stronger for the 16-metre PACER (r=0.87) than the 6MWD (r=0.78). IT showed a significant positive change for waist circumference (–4.3 cm), body fat (–3.8%), systolic blood pressure (–11 mmHg), lipid profile of total cholesterol (–15 mg/dL), HDL-chol (+4.5 mg/dL) and LDL-chol (–9.4 mg/dL), homeostasis model assessment of insulin resistance (–0.6, peak VO2 (+0.2 L/min)), peak Watt (+23.8 W), ventilatory threshold (+21 W, +0.2 L/min), 6MWD (+67.7 m) and muscle fatigue resistance (+6.3 s) when compared with no training (p<0.05) in adults with ID. Moreover IT for the group with ID demonstrated significant improvements for body fat percentage, systolic blood pressure, low-density lipoprotein, fasting insulin, peak VO2, and peak power and ventilatory threshold when compared to CAT (p<0.05). Results of the fourth study, IT in persons with DS, showed that after 12 weeks of training, body mass (–2 kg) and BMI (–0.8 kg/m2) decreased significantly more with IT compared to CAT (p<0.05) in adults with DS. No significant changes were observed for other anthropometrical and health variables between IT and CAT. VO2 peak and time to exhaustion ameliorated significantly in both the IT and CAT compared to control (p<0.05). However, relative VO2 peak improved significantly more than with CAT (p<0.05). Participants in the IT group increased their VO2 peak from 31.9 ± 8 ml/min/kg to 37.3 ± 8 ml/min/kg. Significant ameliorations in functional parameters and leg strength were shown for CAT compared to control (p<0.05). Participants in the CAT group improved their performance in the 6MWD (499 ± 78 m to 563 ± 75 m), 8-foot up and go (5.9 ± 1 to 4.8 ± 1 s) and leg strength (13.1 ± 2 to 15.2 ± 2 number of sit-to-stands). The conclusion that can be drawn from this study is that all 12 functional fitness tests demonstrated excellent test-retest reliability. Both cardiorespiratory field tests indicated sound validity with the gold standard aerobic fitness test. Lastly, both IT and CAT provided significant improvements to physical, metabolic, functional and anthropometric profiles in persons with ID and DS. The influence of IT was more significant on anthropometry and aerobic capacity compared to CAT in adults with ID and DS. However, the impact of CAT was superior on functional ability and lower limb strength in adults with DS. The outcomes of the IT compared to CAT can now shed light on the volume of training (intensity, duration and frequency) that would be ideal for optimal health and functional capacity development in ID and DS populations. Moreover, these changes in the DS population can be monitored with their own unique battery of test items so that exercise or lifestyle changes can be tailored individually to specific strengths and weaknesses of the participants.
- Health Sciences