During a 3-mile run, your feet slap the ground 1,500 times and endure a collective 900 tons of force. Yet the only thing protecting them is a flimsy plastic insole. Shock Doctor Footbeds ($25; www.shockdoc.com) are a multifeature upgrade, using high-tech materials to provide relief from foot fatigue, pronation, and heat. Just pull out your old insole and slip in the Shock Doctor. Here's how it works.