I wish I could tell you where I read it (I tried to google, but didn't get much) but ages ago in a book I read that boys open up more when they are active. I have found this to be true with my sons. So a heavily physically active situation that goes on for some time helps them to be more verbal. I can't recall the reasoning, although it was explained. I will look for the book. I do recall the look of the cover, hoping I will find it for you.
So for us what helps is bike riding together, chopping wood would be good at the age you are talking. We are just starting that. Any physical labor that is enough to get you a little winded, but still able to talk is good, so we do things like digging, or moving rocks around the property (I do actually use that to cut back grass/weed). It has the opposite impact on me (I don't feel like talking when working hard, but I do see in my boys it seems to help. If I recall right it has something to do with engaging the portions of the brain that inhibit openness and that by simultaneously talking while being so active makes it more likely to let your guard down a bit. Again, I can't recall anything more specific, so I will dig and see if I can locate that book. It was quite helpful to me and it was gifted to me by a mom of boys who felt it had helped her a lot.