I would like to add that not only do you need to learn how to deliver atemi correctly and at what specific vital targets, but you need to practice very regularly and in my opinion toughen up the hands and feet so as to be able to deliver atemi techniques with power. The skin, the knuckles, the wrists, the finger tips and toes (if you use spearhand and toe kicks) need to be hardened. The wrists need strengthening so they don't collapse with a punch. I use a makiwarra, leather punching bag without gloves and a canvas bag filled with no. 3 leadshot (for nukite strikes) to strengthen my hands and feet for atemi. For blocking practice, I get a training partner to strike me randomly with a shinai (bamboo sword) which is great for reflexes and it also toughens the body up.
Rather than condition the feet /hands by punching bags etc why not concentrate on speed , correct form and accuracy in delivery of attack/defence movement?Too much makiwara training could result in the development of arthritis .Why get spmeone to hit you with a shinai?How are your reflexes being trained if indeed the you get hit?If you have good reflexes surely the opposite should be happening ie you do not get hit?Do you get bruises?I much prefer getting hit with a feather duster myself.Of course maybe you like a bit of pain???When I need a bit of pain I watch the X Factor or a party political broadcast.