Postural balance, physical activity and capacity among young people with intellectual disability

The overall aim of this thesis was to investigate postural balance, physical activity, physical capacity and their associations in young people (16-20 years) with intellectual disability (ID), mild to moderate. The aim was also to study the reliability and concurrent validity of postural balance tests. To evaluate postural balance, one assessor used five common postural balance tests and one new test. The tests were performed twice for 89 young people with ID (one to twelve days apart). Intraclass correlation coefficients greater than 0.80 were achieved for four of the common balance tests: Extended Timed Up and Go Test (ETUGT), Modified Forward Reach Test (MFRT), One-Leg Stance Test (OLS), and a Force Platform Test (FPT). The smallest real difference ranged from 12% to 40%; less than 20% is considered to be low. For the six balance tests, the concurrent validity varied between none to low. Falls are more common for young people with ID compared to young people without ID. One reason could be impaired postural balance. The postural balance for young people with ID has not been thoroughly investigated. Therefore, five balance tests and three muscle strength tests were used to compare young people with ID with an age-matched control group without ID (n=255). The young people with ID had significantly lower scores on most of the postural balance tests and muscle strength tests of the trunk and lower limbs. Muscle strength, height, and body mass index had no strong association with postural balance. The results also illustrated that young people with ID did not rely more on vision for their balance ability compared to peers without ID. It seems that postural balance is impaired for young people with ID when evaluated with common tests. An everyday situation is to react to unexpected balance disturbances to avoid falls by using different postural responses. Since young people with ID seem to fall more often than peers without ID, it is valuable to investigate if those postural responses are different between the groups. Therefore, young people with and without ID (n=99) were exposed to six backward surface translations and several postural muscle responses were evaluated: muscle synergies and strategies, muscle onset latency, time-to-peak amplitude, and adaptation. The responses of the investigated muscles – the gastrocnemius, the biceps femoris, and the erector spinae L4 level – were measured using electromyography. The results showed that there were no differences between the two groups with respect to synergies or strategies, muscle onset latency, and time-to-peak amplitude. An overall pattern was seen, that young people with ID adapted their muscle response slower in all three muscles than peers without ID, but this pattern was not statistically significant. Studies have shown that people with ID have impaired postural balance, a lower level of physical activity, and lower aerobic capacity compared to people without ID. The association is however not investigated. Therefore, postural balance (postural sway indirectly measured with the subjects standing on a force platform), physical activity (measured with a pedometer), and aerobic capacity (measured with a sub-maximal ergometer cycle test) were used to assess young people with and without ID (n=106). To investigate the subjects’ view of their own health, the subjects completed an adapted questionnaire that addressed their perceived health. The analysis showed no significant associations between postural balance, level of physical activity, and aerobic capacity. The subjects in the ID group, both men and women, had significantly lower aerobic capacity compared to subjects without ID. The answers from the health questionnaire did not correspond to the measured outcomes from the physical tests for young people with ID. In conclusion, ETUGT and MFRT can be used to evaluate change in postural balance over time in young people with mild to moderate ID. The low concurrent validity suggests that the postural balance tests probably challenge various subsystems. Young people with ID have impaired postural balance and perform lower on muscle strength tests than age-matched controls. Postural muscle responses after external perturbations seem to be similar for young people with and without ID, but the ability to adapt muscle responses after repeated perturbations appears to be slower for young people with ID. The studies in the thesis also indicate that young people with ID have reduced level of physical activity and lower aerobic capacity. The lack of association between the different physical functions indicates that they should be evaluated and exercised separately. Young persons with ID might have more difficulty realising the health advantage of being physically active, as they do not seem to make this connection. Because of this, it is important that parents/guardians, school staff, physiotherapists, and others encourage them to participate in physical activity