November/December 2011 

Exercise found to improve memory

Regular aerobic exercise—such as cycling, jogging, running, swimming and playing sports—has many benefits, including strengthening the cardiovascular system, maintaining a healthy weight and improving mood.

Experiments with mice have found that exercise improves their capacity to learn and remember information. Researchers have found that physically active HIV-negative older people are less likely to experience neuro-degeneration than people who are not physically active. This suggests that exercise may be a simple and useful strategy to help slow the loss of cognitive abilities as people age.

In younger HIV-negative adults, running and cycling have been found to enhance memory. Researchers are not certain how exercise has this effect, but evidence from experiments on animals suggests that the body is stimulated to release a chemical signal called BDNF (brain-derived neurotropic factor). BDNF helps brain cells thrive, supports their development and ability to make links with other brain cells, and plays an important role in strengthening memory. BDNF is produced mostly by the brain but also by the kidneys and, in men, the prostate gland.

Researchers at the University of Dublin, Ireland, conducted experiments with 47 young HIV-negative and healthy men who prior to the study did not engage in aerobic exercise. During the study the men engaged in intensive cycling (to exhaustion) lasting from three to up to 30 minutes— this is called acute exercise. In another part of the same study, the men engaged in regular, supervised, more moderate cycling, lasting between 30 and 60 minutes, three times weekly for five weeks (moderate exercise).

The researchers found that both acute and moderate exercise improved learning and memory in neurocognitive assessments. A shorter duration of moderate cycling for three weeks did not enhance memory and learning. The exercise-associated improvements in learning and memory were linked to increased levels of BDNF in the blood. Five weeks of moderate-intensity cycling were linked to improved cardiovascular fitness and lung capacity.

Other experiments with people suggest that regular exercise can increase the size of a part of the brain called the hippocampus. This growth in size is likely due to the formation of new brain cells. The Irish researchers suggest that it is not only the growth of new brain cells but the connections made between brain cells—forming a network—that are important and this may be why exercise takes weeks to exhibit its neurocognitive benefits. It is also possible that part of the reason for the improvement in learning and memory associated with exercise is that the flow of oxygen-rich blood to the brain improved because of exercise.

Although all of the work described in this report is based on experiments with HIV-negative animals and people, there is no reason why regular aerobic exercise should not benefit HIV-positive people. Until well-designed large studies are done with HIV-positive people to explore the neurologic impact of medium- and long-term aerobic exercise, HIV-positive people can discuss with their doctors what forms of aerobic exercise are suitable. At a minimum, exercise can help control weight and reduce cardiovascular risk.

—Sean R. Hosein


  1. Knaepen K, Goekint M, Heyman EM, et al. Neuroplasticity—exercise-induced response of peripheral brain-derived neurotrophic factor: a systematic review of experimental studies in human subjects. Sports Medicine. 2010 Sep 1;40(9):765-801.
  2. Griffin ÉW, Mullally S, Foley C, et al. Aerobic exercise improves hippocampal function and increases BDNF in the serum of young adult males. Physiology & Behavior. 2011 Oct 24;104(5):934-41.