Inclusion Criteria:  Core exercise group and Tai Chi exercise group  healthy community-dwelling older adults (60-74 years old) not received any core stability or Tai Chi Chuan training within the previous 6 months independent in basic daily living activities able to move freely without any assistance Young adults group a. Their age should be ranged between 20 - 59 years  Exclusion Criteria:  All group  have a history of orthopedic surgery on spine or lower extremity have any spine pathology (e.g., spondylolisthesis, disc herniation) have a pain over back or lower limbs to affect the ability to perform activities of daily living had a history of vestibular disease (e.g., Meniere' s disease)