I saw a related article this morning and will attach it here.
Exercise helps memory and thinking through both direct and indirect means. The benefits of exercise come directly from its ability to reduce insulin resistance, reduce inflammation, and stimulate the release of growth factors—chemicals in the brain that affect the health of brain cells, the growth of new blood vessels in the brain, and even the abundance and survival of new brain cells.
Indirectly, exercise improves mood and sleep, and reduces stress and anxiety. Problems in these areas frequently cause or contribute to cognitive impairment.
Many studies have suggested that the parts of the brain that control thinking and memory (the prefrontal cortex and medial temporal cortex) have greater volume in people who exercise versus people who don’t. “Even more exciting is the finding that engaging in a program of regular exercise of moderate intensity over six months or a year is associated with an increase in the volume of selected brain regions,” says Dr. Scott McGinnis, a neurologist at Brigham and Women’s Hospital and an instructor in neurology at Harvard Medical School.
In general, the authors of fitness articles are reluctant to quote pulse rates to aim for. Maybe they’re worried about litigation.
The following link is one of the few exceptions. Here are some calculations for a 40-year-old:
Aerobic heart rate for fat-burning = 130 -150 per min
Aerobic heart rate for fitness = 155 -165 per min
None of these mention the aerobic rates that might relate to memory improvement. Maybe the lower value for your personal fitness rate might be the way to go.
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The link recommended by @Josh recommends “120 minutes of moderate intensity exercise a week”. As usual, they avoid being specific.
The following link mentions MET:
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Exercise experts measure activity in metabolic equivalents, or METs. One MET is defined as the energy it takes to sit quietly. For the average adult, this is about one calorie per every 2.2 pounds of body weight per hour; someone who weighs 160 pounds would burn approximately 70 calories an hour while sitting or sleeping.
. Obesity • The Nutrition Source
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Thanks.