A majority of players rest the thumb on some anchoring spot on the body, most often on top of a pickup. Others rest their thumb on their lowest string or have thumb rests on their instrument. A good alternative for resting the thumb against a pickup is to rest it across the strings, the so-called floating thumb technique.
Both techniques are physically okay, but only if
Flexing te wrist subtly and keeping it to the right slightly are even better, since they are closer to the neutral position of the wrist. The visually straight wrist is not the neutral position! The neutral wrist position can be found by letting your arm hang down at your side and relax. If you bring the wrist up in that same relaxed position, you will notice that the wrist is both flexed and curved sideways to the little finger a little.
With both anchored and floating thumb technique, some variation is desirable. Try to not remain in the exact same position for too long.
When plucking, it is absolutely bad to have your hand and arm in a Z-shape: upper arm against the side of your body, forearm leaning on the edge of the bass’ body, wrist flexed down sharply to the strings and fully curved to the right side to complete the horror scenario. The Z-position is often seen with players who strap their bass high. Resting the arm on the bass will put pressure on the hand tendons that run on the inside of the forearm. Flexing the wrist down sharply is at a high risk of carpal tunnel syndrome. Keeping the elbow fully flexed may cause cubital tunnel syndrome.
The plucking hand should be kept in an almost straight line with the forearm, the elbow away from the body. The hand is to be held in a 90 degree angle with the strings. Strapping the bass high will result in a much wider, technically inferior angle. This wider angle often leads to constantly bending the wrist to the pinky side all the way. This is a very bad habit. You are risking wrist tendonitis.
Resting the thumb is advisable only for some steadiness or orientation of the hand, not to rest the arm on it, and surely not to keep the bass balanced! Use the shoulder muscles to carry the arm. To prevent leaning, better keep the thumb against the pickup, not on it. If you really cannot play like that, you have the bad habit of leaning on your thumb. Start to change your technique immediately! Resting the thumb on the lowest string is much less risky. The thumb might also serve to mute it.
For fast play, some more distance between hand and strings may be preferred. Do not simply press the hand away from the body using the thumb while you allow your elbow to hang down! Instead, move forward the entire arm from the shoulder, concentrating on the elbow. Rest the tip of the thumb lightly against the instrument or, even better, on the lower strings you wish to mute for that passage. This position may also serve to create a healthy change of hand position every now and then.
This technique saved many players from hand injuries. It makes muting easier, especially on instruments with five strings or more. Also here, the shoulder regulates the position of the hand. It is essential to not allow the elbow to lean back on the edge of the body, putting pressure on the hand tendons and limiting the ability to move the hand up and down across the strings.
Like with the anchored thumb, if some distance between hand and thumb is desired for playing fast, gently rest the tip of the thumb on a string.
The swing of the fingers should come from the middle joint, not from the joints at the knuckles. In swinging the fingers from the middle joints, the other joints move in support. In swinging from other joints you will put pressure on them, as there is no support. This may cause the outer phalanx (distal phalanx) to be pressed backwards when plucking the string.
An exercise to improve the dexterity of the middle finger joints:
Slapping is a great technique for both musical and physical reasons. Alternating between slapping and plucking is very good to prevent repetitive strain injuries.
There are three main slapping positions.
This last technique may also be considered as a variation on thumbing.
In all three positions, the arm has to be kept very relaxed to make slapping work. It is lifted by the shoulder muscles, the elbow is brought out and the wrist kept straight, just like when you are plucking in the correct way. The axial rotation of the hand originates from the elbow, not from the wrist as is sometimes suggested. The hand should not be squeezed, but kept a little open and relaxed.
Slapping with the thumb pointing down brings along several advantages:
Slapping with the thumb pointing upward will imply changes to left hand technique as well. Many players turn their bass to a more horizontal position. If elbow and shoulder are still able to cooperate like they should, there is no problem.
Some players prefer to mute their strings placing the side of their hand on the bridge saddles and play with the thumb and one or two fingers. Resting the weight of the arm on the palm will cause strain in the forearm. Also with this technique, it is the shoulder muscles that should keep the arm in position.