The first weeks of a new exercise routine can be hard — your muscles tremble, your lungs burn, your heart races. But after a month or two, it gets easier: You’re running faster and longer, or lifting weights with more ease. You’ve hit a workout plateau. After just a few training sessions, the brain can become more skilled at telling muscles to move. For example: “The heart gets stronger and better at pumping blood to the muscles,” said Jeff Horowitz, an exercise physiologist at the University of Michigan.

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Persons: Chris Perrin, “, ”, Jeff Horowitz Organizations: Washington , D.C, University of Michigan Locations: Washington ,