Your bi's and tri's will get involved on non arm training days at first to a certain extent if you don't bave that mind/muscle link down. Which means that you have the ability to focus on a particular muscle group without getting your other muscles to much involved. To work on this mind/muscle link, drop the weight down a little and do more reps. Try to really focus your mind on the muscle that is being worked . After working on the mind/muscle link for a while, it will become secound nature. For example, after doing an intense back workout my back is sometimes so sore that I can barely move it the next day! However after the same back workout, my biceps are not sore at all. This is because I can work my back muscles without working my biceps. Therefor I have a much better back workout than most people who don't have this mind/muscle link down.

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The more you know, the more you grow!