>> i love to barefoot run. >> a lot of people say it's a fad. you studied this. you studied the way we evolve and what's happening to your body when you run. do you think it's a fad? >> well, if it's a fad it's about a 2 million old fad and we've been running for millions of years and shoes were only invented recently. but most of us grew up wearing shoes and we're not adamanted to be fair foot. we don't have the strength in our feet. if you've been running with shoes all your life and you decide to take your shoes off and go barefootist, you have to cautiously adapt your body. >> some of the same principles, quicker cadence, run quietly, don't overextend, those things very much apply when you're barefoot running. >> it's even more important when you barefoot run. a running shoe has all sort of features to protect you. if you are going to land our heel, you want a shoe like this with a lot of cushioning, it will protect you from the high forces. >> yes. >> what matters most is how you run not the kinds of shoes you