Q: Just a comment on 2447. With machines you don't have any gravity pulling your arms down like you would if you were exercising your biceps with barbells.

A: Well, gravity is still there, but machines typically work your arms at angles different from freeweights, and, say, 60 pounds on one machine will certainly feel very different from 60 pounds of freeweights. So overall experience with machines will feel very different from freeweights, even if you are doing the same number of reps to failure.