Questions 79-84 based on the following passage.

    Regular aerobic exercise such as walking may protect the memory center in the brain. Meanwhile, stretching exercise may cause the center called the hippocampus to shrink, the researchers reported. A study involving men and women in their mid-60 shows that walking three times a week for a year increased the volume of the hippocampus, which plays an important role in memory. On the other hand, the control participants who took stretching classes decreased in the volume of the hippocampus. The findings suggest that it is possible to evercome the agerelated decline in hippocampal volume with anly moderate exercise, which leads to better fitness and perhaps to better spatial memory.

    The researchers noted that the volume of the hippocampus falls with age by between 1 percent and 2 percent a year, which lead to impaired memory and increased risk for dementia. However, animal research suggests that exercise reduces the loss of volume and preserves memory. To test the effect on humans, they enrolled 120 men and women in their mid-sixties and randomly assigned 60 of them to a program of aerobic walking three times a week for a year. The remaining 60 were given stretch classes three times a week and served as a control group. Their fitness and memory were tested before the intervention, again after six months, and for a last times after a year. Magnetic resonance images (MRI) of their brains were taken at the same time in order to measure the effect on the hippocampal volume.

    The study showed that overall the walkers had a 2 percent increase in the volume of the hippocampus, compared with an average loss of about 1,4% in the control participants. The researchers also found that improvements in fitness measured by exercise testing on a treadmill were significantly associated with increases in the volume of the hippocampus.

    the other hand, the study failed to demonstrate a group effect on memory. Both groups showed signficant improvements both accuracy and speed on a standard test. The apparent lack of effect is probably a statistical thing that results from large individual differences within the groups.

    The analyses showed that higher aerobic fitness levels at baseline and after the one-year intervention were associated with better spatial memory perfomance. They found that change in aerobic fitness was not related to improvements in memory for either the entire sample or either group separately. On the other hand, larger hippocampi at baseline and after the intervention were associated with better memory performance. The reseachers have drawn a conclusion that aerobic exercise is neuro-protective. Starting an exercise routine later in life is then useful for either enhancing cognition or increasing brain volume.

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Which of the following best restates the idea in paragraph 5?