Strength and agility training in adolescents with Down syndrome: A randomized controlled trial

Abstract

The purpose of this study was to investigate the effects of a proposed strength and agility training program of adolescents with Down syndrome. Ninety-two adolescents were recruited and evenly randomized to two intervention groups (exercise group vs. control group). The mean age for the exercise and the control group was 10.6 ± 3.2 and 11.2 ± 3.5 respectively. The exercise training program consisted of a 5-min treadmill exercise and one 20-min virtual-reality based activity administered three times a week for 6 weeks. Pre- and post-test measures were taken for muscle strength and agility performance. The measured muscle included hip extensor, hip flexor, knee extensor, knee flexors, hip abductors, and ankle plantarflexor. A handheld dynamometer was used to measure the lower extremities muscle strength, and agility performance was assessed by the strength and agility subtests of the Bruininks–Oseretsky Test of Motor Proficiency-Second Edition. The exercise group had significant improvements in agility (p = 0.02, d = 0.80) and muscle strength of all muscle group (all p's < 0.05, d = 0.51–0.89) assessed in comparison to the control group after the 6-week intervention. Knee muscle groups including both flexors and extensors had the greatest gains among all the muscles measured. A short-term exercise training program used in this study is capable of improving muscle strength and agility performance of adolescents with DS.

Introduction

Down syndrome (DS) is a chromosomal anomaly with incidence of around 1/700 to 1/1000 live births (Roizen, 2002). DS is the most common single cause of intellectual disabilities (ID) (Menkes & Falk, 2005), with between 70% and 75% of individuals with DS attaining an IQ of between 25 and 50 (Vicari, 2006). Individuals with DS are mainly characterized by several clinical symptoms including orthopedic, cardiovascular, musculoskeletal, and perceptual impairments. DS are associated with a distinct profile of developmental outcomes regarding body functions and activity performance (Fidler, Hepburn, Mankin, & Rogers, 2005), with evidence for great variation in the range and level of deficits resulting from biological and environmental factors (Turner & Alborz, 2003).

Individuals with DS generally show deficits in motor skills throughout development (Palisano et al., 2001). Most infants and toddlers with DS show extreme delays relative to age-matched typically developing infants, moving through stages of early motor development more slowly and exhibiting more within-group variability than typically developing infants (Bertoti, 2008). In older children with DS, motor problems persist. Adolescents with DS have specific impairments in fine motor function, including difficulty with precise finger movements as well as gross motor tasks such as sit-ups and push-ups. Other studies have described their deficits in visual motor integration, agility, muscle strength, motor control, and movement reaction time (Rigoldi et al., 2011, Welsh and Elliott, 2001, Wuang and Su, 2012).

Among the motor impairments demonstrated by individuals with DS, muscle strength is one of the essential abilities of individuals to achieve effective and functional movements. Muscle weakness and hypotonia are theorized to impair upper extremity midline movements and gaits (Lewis & Fragala-Pinkham, 2005). Particularly, the lower extremity muscle strength of individuals with DS is of fundamental importance to their overall physical health, and ability to perform daily activities (Gupta, Rao, & SD, 2011). Further, because their workplace activities typically emphasize physical rather than cognitive skills, decreased strength can negatively impact the vocational and social development of adults in the workforce (Shields, Taylor, & Dodd, 2008). However, individuals with DS demonstrate lower levels of muscle strength than those with ID without DS and those without ID (Cioni et al., 1994, Horvat et al., 1997, Mercer and Lewis, 2001).

Agility is the ability to move and change direction and position of the body quickly and effectively while under control, and requires the integration of isolated movement skills using a combination of balance, coordination, speed, reflexes, strength, endurance, and stamina (Sheppard & Young, 2006). Individuals with ID including DS are deficient in carrying out tasks requiring agility such as shuttle run and vertical jump (Wuang, Wang, Huang, & Su, 2009). Additionally, comparing to other developmental disabilities, individuals with DS have poor performance in praxis skills which are the key elements to agility performance (Fidler et al., 2005).

Studies done to determine the effect of strength training in DS have focused on the child and adult population. In adults with DS, Tsimaras and Fotiadou (2004) found a significant increase in leg muscles strength following a 12-week intervention while Shields et al. (2008) demonstrated gains in upper extremities muscles strength after completing a 10-week group progressive resistance training program. A recent study (Gupta et al., 2011) suggested that a 6-week exercise training program may improve the lower limb muscle strength in children with DS. Agility training in children with DS is less discussed, Wuang, Wang, et al. (2009) found the improved performance on the BOTMP agility subtests after a 6-month sensorimotor training in children with general ID including DS. They also implemented virtual-reality based programs in DS lately and found significant gains on the BOT-2 strength and agility subtests comparing to those receiving traditional occupational program only (Wuang, Chiang, Su, & Wang, 2011).

Even though the above-mentioned programs documented benefits in improving the muscle strength and agility performance in DS, however, the programs might not be sustained because of the long intervention period or complicated program contents. For example, in Lewis and Fragala-Pinkhams's study (2005) on the effects of aerobic conditioning and strength training program, most participants switched to a simple treadmill training program after the study ended. As well, participant compliance with exercise decreased rapidly over time (Schutzer & Graves, 2004). Therefore, a shorter period of training program (e.g., 6 week in the present study) might be more feasible, accessible, and efficient for individuals with DS (Gupta et al., 2011, Wang et al., in press).

Appropriate use of commercially available equipment or products make physical training programs more accessible and fun for individuals with disabilities. Several intervention programs were implemented over the years with some using the treadmill. These programs achieved improvement in various fields, such as muscle tolerance, physical fitness lower pulse per minute, and muscle strength in particular (Chanias et al., 1998, Merriman et al., 1996). Treadmill has been used in physical fitness training programs on DS and other ID as well. A short-term daily treadmill exercise conducted by Lotan, Isakov, Kessel, and Merrick (2004) produced significant improvements in physical fitness and functional ability for children with ID after 8 weeks. Aged adults with DS can significantly improve muscle strength and balance by adopting suitable programs of treadmill walking as well (three times a week for 25 consecutive weeks) (Carmeli, Kessel, Coleman, & Ayalon, 2002). However, due to their cognitive limitations and lower physical fitness, individuals with DS might be more able to adhere to treadmills exercise protocol with shorter walking time (Carmeli et al., 2003, Wang et al., in press).

Clinical practitioners have kept trying to use more appealing therapeutic equipment to address the motivation and attention limitations identified for individuals with cognitive impairments. Serious studies (Lotan et al., 2009, Lotan et al., 2010, Wuang et al., 2011) incorporated the virtual reality based (VR-based) activity into the regular exercise programs and also demonstrated improvement in physical fitness (e.g., muscle strength) and motor functions (agility performance) for individuals with developmental disabilities and ID. The averaged intensity of these VR-based activities was 45 min per week for 16 weeks. They also found that children playing in VR-based activities felt safe and were able to practice; playfulness was increased if the child had some control and allowed creativity and persistence with the VR's task. Compared to treadmill exercise, VR-based activities focused more on training components essential for agility performance such as postural control, weight shifting, and dynamic balance.

To date, scant data is available on exercise training programs involving a substantially larger sample of adolescents with DS. Improvement of muscle strength and agility performance in adolescents might lead to a more productive and active lifestyle in adulthood with DS. In light of the therapeutic values of both treadmill and VR-based exercise and their combining effects (Wang et al., in press), this study aimed to conduct a clinical trial to evaluate the effectiveness of a combined program of strength and agility training by using treadmills and Wii game protocols. We hypothesized that the short-term exercise program is effective in improving muscle strength and agility in a cohort of adolescents with DS.