This adds a new twist to why they might take young blood.

Blood from athletic mice may give a brain boost to couch potato rodents

Slacker mice don’t have to lift a paw to reap the brain benefits of exercise. All they need are injections of blood from their fellow rodents that have been working out, a new study reveals. The research suggests a molecule in the exercisers’ blood can replicate some perks of physical activity, including reducing the brain inflammation that may promote illnesses such as Alzheimer’s disease.

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https://www.science.org/content/article/blood-athletic-mice-may-give-brain-boost-couch-potato-rodents