How we hold an object has everything to do with the force our fingers can produce. Posture of the wrist can change up to 70% of the hands force producing capabilities. To what degree the wrist is positioned affects muscle lengths and the moment arms of the fingers. To further understand this concept take your wrist and extend it, the fingers naturally curl into a somewhat grasping position, contract the finger flexor muscles and this will automatically generate a wrist flexion moment.
Each finger operates and controls the hand in what manner this is accomplished varies between yourself and each individual. The way we are capable of muscle combinations to achieve similar kinematic outputs is due to the number of muscles and their redundant control in interacting with objects.
In wrist extension the EMG activity of every finger extensor muscle is the highest and when the wrist is flexed the lowest. When moving the hand in various positions from neutral, to palm up and down finger electrical activity becomes variable. When the wrist is palm up, finger extensor EMG activity varies the least among digits. Finger flexor muscles like extensors are affected by wrist angle. Finger flexors are the most active when the wrist is flexed.
Wrist Extension Resisting Finger Extension - Lowering Phase of an Isometric Hold on the Pendulum Power Grip Pro