Many factors influence the strength of grasp. Actual strength will vary with age and sex. A strong grasp reflex is present at birth. A baby begins to develop control of strength around the age of 2 as appreciation of the friction between skin and object develops. Gloves produce a significant drop in grip strength.
Proper grasp is dependent upon appropriate lengths of the constituent bones of the palm and digits.
These lengths are in fact proportionally related and determine the form and shape of grasp. When grasping a cylinder, there is a normal inclination of palmar grasp, a fact unfortunately not well known to the manufacturers of crutches, who still copy the ancient Roman model. Our work has shown that regardless of wrist position, the percentage of total grasp force allocated to each finger is constant. The type of grip used in any given activity is a function of purposeful action and is not dependent on the shape or size of the object grasped. In the latter part of World War II the American army set up 10 hospitals in the USA for the exclusive treatment of upper-limb injuries.