Multi-finger ab-/adduction is a unique task of strength and coordination, and is much different than other specific grips. The muscles on the inside of the fingers contract to facilitate a controlled motion. These muscles are utilized while picking up almost every object and in performing most tasks involving your hands.
Take a light dumbbell in your hand and hold the bell vertically, then slowly rotate it parallel, or below parallel, to the floor turning your palm so it faces upward (supination). As you do this movement, back and forth, you are able to feel the inside of your fingers contracting to control the weight. The palmar interosseous muscles adduct or bring the fingers together. The dorsal interossei abduct, or spread, the fingers of the hand.
In hand training, we use hand grippers to train the power grip, yet, holding on to an object as it is being pushed toward you, or pulled from you (such as grabbing someone around the wrist) requires powerful ab-/adducting digits that can apply tremendous force in multiple directions.
To train finger abduction and adduction pick up a wooden handled sledge hammer with your finger tips. Starting at the top of the handle work your way down to the metal head of the sledge using only your index, ring, middle and pinky fingers. Once you are able to touch the end of the mallet keep your fingertips on the handle, and let the hammer slide between your fingers back to the starting point. This will be an eccentric movement, and is an important part of Getting your fingers Strong. When you are capable of walking down the sledge hammer twice - add weight.
A 43 pound ‘finger walk’ give it a try