Dynamic balance indexes of the subjects in control (cont) and experimental (exp) groups. OBI: overall balance index; API: anterior/posterior index; MLI: medial/lateral index. Lower values indicate better balance. The difficult levels of the balance tasks for the five tests (week 0, week 4, week 8, week 12, week 24) were different, thus they were not comparable among the five tests. *P < 0.05, **P < 0.01.