I can see where a little stretching would help. I have encountered folks who cramped up in their forearms, and even in their hands, after a period of picking. I won’t rule out that part of their problems may have been related to a medical condition, such as a lack of potassium, but a little stretching might’ve helped. I mention the potassium because, if you’d question them farther, most of them also had problems with leg cramps and such. I’m no doctor. I don’t even play one on TV, but it’s been said that cramps can be relieved by certain things. If you have problems with cramping, you may want to ask your doctor.
No doubt about it, picking is exercise. Not only does it exercise the mind, it exercises the muscles, as well. It only makes sense to do what you can to help develop those muscles. I’ve known musicians who used those “finger exercise units”. Maybe you know what I’m talking about. They’re spring loaded and you squeeze them to strengthen your hands.
Also, I have been told, by at least a couple of “old timers”, that they used to squeeze balls of wax to strengthen their hands. They claim this really worked and the nature of the wax wouldn’t allow them to over-do their exercise sessions. Seems the more you work with the wax, the warmer it gets and the softer it gets. Pretty soon, it’s too soft to work with and you have to lay it down for awhile. I don’t know from first hand experience. All I know is what they told me about it.
Speaking of muscles, don’t forget that picking sometimes requires a lot of standing. You need to pay attention to your back. Good posture really helps. It’s entirely too easy to slouch over so you can see the strings. With a heavy banjo slung over your shoulder, this puts a lot of strain on your back and your neck. If you’ve got to look at your strings while you pick, then you should take every opportunity to pick from a sitting position. There’s no real reason to practice standing up, unless you feel that doing so helps you when it comes time to render a standing performance. It’s never bothered me to practice sitting down…or lying down. (I’ve done a lot of practice lying down on my bed.) Never mind the other guys calling you a sissy. When you’re older, you can stroll past them with your head thrown back and your chest out while they shuffle along like crabs. Living well is the best revenge.
I used to have problems with my finger joints “popping”. I’ve never been one to “crack my knuckles”, but after a certain amount of picking time the joints would take it upon themselves to spontaneously “pop”. Talk about a pain! Used to be I’d take a little time before going onstage to try and pre-pop those joints. Most times, I couldn’t do it. I dreaded it happening onstage. Guess that’s what they mean by suffering for your art.
Getting back to doctors, most physicians familiar with stringed music will tell you not to perform or practice more than six hours in any given twenty-four hour period and to take a thirty minute break after every two hours. This helps prevent damage to the finger joints as well as to the ligaments and tendons. I guess most of us have heard about “carpel tunnel syndrome”. Turns out there are other things that can afflict musicians, too.
Shucks, I’ve walked into the studio, started to work and looked up twenty minutes later, only to find 12 hours have gone by. Time flies when you’re having fun, and that’s the truth. I’ll bet any musician can tell you about those “all nighters”. Bluegrass festivals spawn such things. You get done with the last show of the evening, after having picked all day long, and you get into a jam session that lasts till 4:30 or 5:o’clock in the morning. You go to bed, get up in time for an 11:am show and don’t stop picking till sometime just before sunrise, next morning. I used to do that in my younger days. These days, at 50 years old, I sometimes wish I hadn’t.
But then, what the heck. Forget the aches and pains. Enjoy your music while you’re young. Everybody’s going to get old, if you’re lucky. As Paul says, “Pick ‘em if you’ve got ‘em.” And, I say, “enjoy it while you can”. Don’t take life too seriously. You’re not going to get off this planet alive, anyway.
-Jesse

About training your fingers to fret only on string at a time, it may help to think of your fingertips as having more than one surface. I mean, compared to the thickness of a banjo string, your fingertips are like a bar room carpet with a pool stick lying on it. The stick has a lot of room for repositioning.
Try this, make a Chord. Now, remove your fingers from the neck and look at the tips of those fingers. You might expect to see that your strings fall in the center of your fingertips, but it could be they don’t. From the impression made by the strings you can see that you have plenty of room on your fingertips to reposition where the string touches. If your finger is interferring with the string next to it, think about that groove you just saw and make an effort to adjust that fingertip either “above the groove” or “below the groove”. This will help you gain that “fraction of clearance” necessary to avoid “muting” a neighboring string. Practice will help your fingers determine where to make contact. As your Chord Positions change, so may the need for your fingertips to be readjusted so as to properly form that Chord Position. My fingers don’t hit in the same groove all the time. It’s necessary to adjust their positioning to accomodate the technique being performed.
By the way, this goes for those of you having trouble making “Bar Chords”, too. Look at your finger and see where the strings are falling in relation to the “joint creases” in your finger. If necessary, think in terms of repositioning those grooves left by the strings. In time, you’ll learn to make Barred Chords with any of your four fingers.
One more thing to think about, the “elevation” of your Chording Hand will have a bearing on both your accuracy of finger placement and upon the force you can exert. Try raising or lowering your hand as you perform your Chords and other performance techniques. Your Chording hand can also be “twisted” in relatinship to the banjo neck, as necessary.
Practice doesn’t make perfect. “Perfect practice” makes perfect.
-Jesse