The power grip is a grip formed with the fingers and the palm of the hand; it is used for grasping with high force and low precision because it uses the bulk of the hand for generation of force rather than the strength of individual digits. 

 

Once an object is grabbed and squeezed with the power grip and the object is trying to pull away, the abductors and adductors of the fingers must be strong. The dorsal interossei muscles in the back of the hand act to spread or abduct the index, middle and ring fingers away from the hand's midline; they also assist in flexion. The palmar interossei muscles of the hand adduct the thumb, index, ring and little fingers toward the middle finger. These appendages if developed make the power grip much stronger and more functional. Then when an object is grasped there is much less chance of it going anywhere.

Pendulum Grip Cart
Sledge Hammers on the Pendulum Grip Cart

To strengthen these important often neglected muscles start with a six pound wooden handled sledge hammer. Standing or in a seated position from the top of the handle, pick up the hammer with the distal and middle phalanges. Walk your fingers down the handle with the goal of touching the sledge. Movement is made by one hand until the index finger reaches the pinky of the opposing hand then the other hand begins movement. Once at the bottom, sledge touched, let the sledge hammer slowly return to the starting position by resisting it sliding between the fingertips of both hands. This slow return to the starting position is eccentric loading of the musculature. When you can achieve two reps add weight by slipping a 2.5 pound plate over the top.

If an athlete regularly trains their power grip and can also finger walk a 20 pound sledge, their hand strength is well above average. When an athlete can finger walk 40-50 pounds they will actually be able to bend steel like a professional strongman.

Pendulum Grip cart grip strength
The Sledge Hammer Finger Walk with 30lbs