Want to protect your brain from neurodegenerative diseases like Alzheimer's and Parkinson's? It turns out that just six minutes of high-intensity cycling turns on a gene in stressed muscles that produces a small protein called irisin.

Irisin boosts production of another protein called brain-derived neurotrophic factor (BDNF) that is essential for learning and memory, and could protect the brain from age-related cognitive decline. It has that effect because BDNF increases new neural connections and pathways, and promotes survival of neurons.

That, in turn, increases the formation and storage of memories, enhances learning, and boosts cognitive performance — at least in animal studies.

These insights come from research in the Journal of Physiology that looked at the brain benefits of fasting for 20 hours, 90 minutes of low-intensity cycling, a six-minute bout of vigorous cycling, and the combination of exercise and fasting.

Short-but-vigorous cycling boosted BDNF four to five times more than fasting (which caused no change) and prolonged low-intensity exercise (which caused a slight bump).

Another theory (besides irisin production) about why high-intensity exercise works is that it increases blood platelet production by 20%; blood platelets store a lot of BDNF.

This adds to the theory about important it is to get frequent, short periods of activity. One study found that five minutes of walking every half hour offsets some of sedentary behavior's most harmful effects by lowering blood sugar and blood pressure, and reducing blood sugar spikes by 58% after a big meal.

So don't just sit there.