In a self-defense situation, the defender must evaluate what defense or attack is required and what amount of force is required. Intensive training is required before these evaluation may be made quickly and legally. Fear or surprise may make it difficult to execute subtle movements involving fine motor skills, so extensive training is needed to make these movements instinctive.
A 1990 study by University of Illinois researchers found that rats trained to cross rope bridges and pencil-wide beams to increase their coordination, possessed 25 percent more neuron connections to other brain cells that rats who only ran on treadmills.
A 1999 study by researches at the Salk Institute for Biological Studies found that running doubled the number of new brain cells that survived in adult rats.
A 2002 study by Stanford University had 6213 men walk on a steeply inclined treadmill until the point of exhaustion. After tracking the men for the next six years, the study found that the men who tired first on the treadmill test died at a 4 times greater rate then the men who were in the best shape. For every step up in physical fitness, the men were 12 percent more likely to live longer, even when they had other risk factors such as diabetes, smoking, hypertension or high cholesterol.
A 2002 British study of 2,341 women ages 60 to 79 found that doing housework as exercise does not seem to improve health or lower weight or resting heart rate, while brisk walks do. Work, no matter how strenuous, is not exercise. To increase health significantly, physical activity should be performed specifically as exercise, not as work.