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The purpose of present study was to investigate predictions of challenge point theory (guadagnoli and lee, 2004) through comparing two group of challenging and nonchallenging games in developing manipulative fundamental movement skills. Thirty 4 to 6 years old child were selected from one of the kindergartens of Tehran and were grouped according to pretest scores. The games were used were designed for developing manipulative skills in both groups, however the task difficulty of these games was increased in challenging group while in nonchallenging group it was kept constant. The intervention was 8 weeks, 2 session for each week and 42 minutes for each session. Children's manipulative skills were assessed using Test of Gross Motor Development – second version in the beginning and the end of the intervention. The results of multivariate analysis of variance showed  that improvement groups in total score of manipulative skills and all subscales exept that catching wasn't significant. In total, if the challenge point theories predictions on developing of manipulative skills of healthy children failed to be proved but better improvement of challenging group in catching shows that this method is more effective in developing complex skills.

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The aim of present study was to determine the effect of different levels of balance task difficulty and muscle pattern sonification on balance elderlies. eleve  healthy elderly mean age 66/09± 2/26 yr were selected voluntarily. The study inclusion criteria included no structural postural problems, lack of lower extremity fractures over the past six months, no uncorrected visual impairments, no vestibular disorders, and no use of nerve medications, narcotics, alcohol, and any substance leading to dizziness or lack of focus and affecting balance
 Participants were asked to stand still on a stable platform under two conditions (with sonification of muscle activity pattern and without feedback) in three difficulty levels (6, 8, and 10). Stability index scores (Overall, Anterior- Posterior and Medial- Lateral) were calculated by Biodex Balance System.  The duration of each test was 20 seconds and rest times were 10 seconds. Results showed that with increasing task difficulty, scores of  overall balance ,Medial- Lateral balance  and Anterior- Posterior balance. In addition, There was a significant reduction in the scores of Overall balance (p= 0/005), anterior - posterior balance (p= 0/002) and medial - lateral balance (p= 0/022) and sonification of muscle activity pattern condition compared with without sonification of muscle activity pattern condition in the level of 6. Overall, the results of this study showed that increasing task difficulty increases postural sway, and the availability of sonification of muscle activity pattern can improve balance and reduce postural sway.
Keywords: Electrical activity, Stability index, Biofeedback , Task Difficulty