Researchers have determined that 52 hours of exercise over 6 months is the minimum amount needed to improve cognition in older adults. Total exercise time was the most important factor linked to improved processing speed and attention, executive function, and global cognition in a systematic review of 98 randomised controlled trials. This finding suggests that cognitive improvements associated with exercise act on the same constructs affected by cognitive ageing.

Exercising in approximately 1-hour sessions to reach this total was associated with improved cognitive performance in older healthy adults, those with mild cognitive impairment, and others with dementia.

Interestingly, researchers report that cardiovascular exercise, resistance training, and mind-body exercises, or a combination of these, were still advantageous. Running might work for some people, but patients with a bad hip or bad knee could still see benefit from lower-impact activities, such as yoga or tai-chi.  – Medscape Online