I learned this exercise from my classical guitar instructor in Los Angeles, Grammy award winning guitarist Scott Tennant. This exercise can be found in his best selling instruction book "Pumping Nylon" which has sort of become the classical guitarist's bible over the past couple of decades.
In any case, I have adapted those exercises for pick style guitar and demonstrate them in this video lesson.
It is very important to keep the inactive fingers as relaxed as possible. I can't stress this enough, half the battle of independence of the fretting hand is keeping your hand free of tension.
This is a great exercise in developing that. That is not to say that it won't make your muscles sore because it will. But, decreasing as much tension as possible in all fingers while you are doing some of these movements is crucial.
Don't forget to "Grab The Tab" from the link below.
Have fun and make sure to give your hand a break if it starts getting a bit too tired. Many times all you will need to do is just shake your hand out for 10-15 seconds for it to recover enough that you can continue practicing.
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