Is this normal. This is the first week I am targeting my chest/upper body. I noticed a few times my muscles would shake in the middle of a lift. They did not hurt and I was able to finish. I just thought it was odd.
I would guess it would be a sign that you were "working to failure" that point when you are close to not being able to complete a set of reps because the weight is too heavy... just part of the muscle building process... And good feedback from your body that lets you know just how much weight you can lift now...