Studies show that a power grasp of about 5 lbs per in 2 will keep a hammer handle from slipping out of the palm. However, if skin sensory feedback is impaired, then strength has to be increased to provide deeper sensory feedback. The normal palmar surface grip area in an adult is about 10 in 2 . Just as in leprosy, in which the internal forces of grasp destroy the skeleton, so in rheumatoid disease the aberrant forces produced by soft tissue disease disarray the normal forces of grasp. The more the patient increases the force of grasp, the greater the self-destruction of the normal postures of grasp.
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.