i've started doing free weights. i have been doing curcuit training but there is one exercise i find really hurts when i do it. i'm not really that weak or anything at all, just looking to tone up a bit not really gain mass. anyway, i've found that when i try and do tri-cep kick backs it rally hurst the joint of my shoulder loads. the thing is though that it doesn't hurt my tri-ceps as if the weight is too much and i don't even use a heavy weight when it hurt (i tried doing heavier weights but when it hurt dropped down thinking it might be too heavy). the weight i tried to use was only a barbell with 1kg!!!! i don't get it. i can do press ups fine and can do tri-cep extensions. i can also do all of the shoulder exercises, which really confuses me if i have something wrong with my shoulder. its only that one exercise that hurts it. i have stopped it for the time being as i guess if it hurts then it can't be good. any thought as to what might be wrong????????