太重:看你个人的。。。不过很多会有drop set or rest pause on last set ...
focus: form and position very important than weight ....
跳来跳去:是有原因的。。。是为了让你的Muscle不会习惯之前的workout set...shock your muscle fibre ..the way to get muscle bigger...
injured joint mostly due to heavy weight ...try to get someone or your friend in gym as spotter to make sure you do failure reps or sets...
i am not pro ..just giving advises....apology if there is anything wrong here...i believe they are other trainers here as well who might give you more perfect advises ...