Sled dragging is one of my favorite exercises. It's a technically simple exercise - you load up a sled with weights and drag it. I've DIYed my own sled in the past (here is my tire rig sled from when I was living in Japan) and I've pulled manufactured sleds, too. You can use them for a variety of exercises, such as dragging it in on a rope or just simply walk around with one dragging behind you.
Here are some resources for sled-dragging available on the web. I know there is at least on ebook on the subject, but this is a collection of free resources.
Chandler, Brian. Dragging and Pacing (found in Dan John's Get Up newsletter, page 9)
Evan-Esch, Zack. Endless Sled Dragging Variations That Will Dramatically Improve Your Performance
Tate, Dave. Drag Your Butt Into Shape
Wilson, Todd. Sled Dragging Part II: The Fundamentals
Here you can see the crowd at DeFranco's doing something I used to do in Japan - weighting a sled with kids. Mine wasn't so deliberate, actually. I'd load up my sled and start dragging it, and the neighborhood kids decided it looked fun and asked for rides. Soon enough I'd be dragging so many kids I couldn't move the sled. They call that "progressive loading."
大会情報：5/28 JBJJF 第1回北海道柔術オープントーナメント 中島体育センター
1 hour ago