Doing legs will actually improve upper body.
Some find it hard to believe, but it actually makes alot of sense.
To grow, you must create microtrauma, and allow it to recover 2 days per musclegroup.
On the other hand, one trains to trigger hormonal response.
So by doing legs, you are allowing your upper body to recover, but are triggering hormonal response wich will in turn, give enhanced results all over the body.
If you hold the bar correctly, you will also use the shoulders to both carry the weight, and apply pressure to the body, thus using them as a secondary muscle
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I understand, it always feels great when you are in good form.
I think dule mean by form, that he is doing the excercise in the correct way
i can be wrong tho