I think that right before he plants his foot on the ground in front of him, his leg isn't extended forward enough, it looks as though he could trip if he's not careful :S That's the only problem I currently see with the legs.
Also, his arms look a bit too puny, and his chest to beefy; when I look at him, I think lumberjack, so I'd assume his arms would be a bit chunkier. The fact that he looks like a lumberjack to me kind of makes the chunky chest acceptable I geuss, but in his standing pose, his lower chest is sucked in; I don't get it?
Will you be adding more detail, shading, texture, etc? Right now it looks kind of plain, and the upper half of his body lacks shading.
Apart from these issues, it's looking very fluid/dynamic.