Your back muscles (in particular latissimus dorsi), due to their enormous power, must be physically understood, and fully applied in your techniques. The best way to establish how much you use your back muscles (or any specific muscles or joints) is via isolation training. Here are some very simple examples:
Try various tsukiwaza (punching techniques), uchiwaza (striking techniques) and ukewaza (blocking techniques) with complete focus on your back muscles. Execute techniques, both into the air, and against a target. In this process, don’t forget to self-check (experiment) how your other muscles and joints function. Take particular note of your shoulders, chest and abdomen. After this I recommend focusing on your back muscles, and backbone, working collectively. I really recommend training mawashi-zuki and kake zuki in this practice, in addition to the typical straight punches, strikes, and fundamental ‘blocks’. I found mawashi-zuki to be particularly interesting, but I will leave that for you to discover if you haven't already!
My muscle training: Many people have emailed me (since the June article) asking what I do to train my body, and I can honestly say, that I only do karate. For years I have not done any serious weight training, and have relied on body weight exercises, kihon and kata (and to be honest, mostly kihon and kata). My target is 'karate efficiency' as opposed to 'looking nice'. As I stated in June, karate has given me some shape, and that is a byproduct I admit that I am happy about. I'd like to say here, that I'm sure any bodybuilder would have a good laugh, at my photo above (of my back muscles). But in saying that, the muscles I have developed are simply specific to maximize my impact power. I have no desire to have 'ripples' or increase my size.