I started doing farmer's walks 3 months ago as my gym has the implements and I figured I'd make use of them. In 3 months my traps, forearms, and calfs have gotten noticeably bigger. My traps have seen the most growth, and I have gotten comments from 3 people on how much bigger they look. My grip has improved and I can do deadlifts double overhand with about 50 more pounds than I could before training farmer's walks. Something I've noticed is my back feels amazing after doing my sets of farmer's walks. I'm not sure why this is, but Stan Efferding talks about weighted carries helping with restoration of the spine. They will not only build up your traps/upper back, forearms, grip, calfs, and core, they also make great conditioning work. Load up an easy to moderate weight at the end of your workout and do 10-30 sets of sprints with them with minimal rest. If your gym doesn't have the special handles, no problem. Just use a trap bar and throw some fat gripz on the bar to really hit the forearms and grip. I highly recommend putting farmer's walks into your program once or twice a week.