This exercise will comprise stretching, muscle strengthening, and balance training at increasing difficulty levels, tailored and supervised by a physical therapist, and will take place at a subject's residence or in the neighborhood once a week for 6 months. Each session will last 60 min.

The 8-form Yang-style tai chi chuan intervention will take place at a subject's residence or in the neighborhood once a week for 6 months, and each session will last 60 min.

After the baseline, the case manager will visit subjects in this group once for comparability with the other two intervention groups and instruct them to maintain their usual physical activity.

Each session will last 60 min, consisting of 10 min of warm-up, 45 min of exercise, and a 5-min cool-down.

Performance on six gait characteristics (velocity, cadence, stride length, swing time, stride length variability, and swing time variability) will be measured with a 6-m electronic walkway of GAITRite.

Global cognition will be assessed using the Mini-Mental State Examination (MMSE). The MMSE comprises 11 questions, and the score ranges 0~30, with lower scores indicating poorer global cognition.

Serum BDNF concentrations will be assessed.

Serum IGF-1 concentrations will be assessed.

Serum VEGF concentrations will be assessed.

The Tinetti balance score ranges 0~26, with a higher score indicating a better balance ability.

The timed up and go test requires subjects to rise from a standard chair, walk a distance of 3 m, turn, walk back to the chair, and sit down. The time to complete the timed up and go will be recorded.