Walking and running posed no problem in my experience, and these are the first earbuds I've used that managed to stay in my ears while playing disc golf. (9to5google.com)
Because this was super cramped and the headphones they gave you were bad quality and didn't stay in your ear. (seatguru.com)
They come with a useful locking mechanism that helps these earbuds stay in your ear. (geekwrapped.com)