I have been going to the gym and wondering how exactly to use the machine, when you use for example one of those pulley machines do you have to let your arms go all the way up and then bring it down, is full extension a lot better even though i lift less pounds (and do it more times). When i do 70 pounds my extension isnt amazing and neither is my form but its pretty decent. but with 50-60 i could go full extension about 10-30 times (im 15) so what is better?