How Do We Grip?
We take a grip on things by using our muscles to exploit the development of the human thumb. The importance of this thumb is that it can be moved across the palm of the hand to touch the index finger. In contrast the digits of a monkey’s hand are more rigid. This difference explains why a human being can handle an instrument with such precision.
The mechanism of the hand is operated by way of the wrist, a hinge joint composed of eight small bones (carpals) packed firmly together to give elastic stability. Below the wrist project five small, long bones (metacarpals) which give the palm firmness. Four of the bones have hinge joints and are connected to the fingers. But the joint connected to the thumb allows it to move round and meet the fingers and palm, thus providing a firm grip.
Possession of such a hand has enabled man to form a society and culture based on the use of tools. It is thought the hand developed from the five-rayed forepaw of an early vertebrate. However, occasionally a child is born with an extra tiny thumb or little finger and some people believe that the forepaw was originally seven-rayed.
The human thumb has lengthened with evolution and is much longer in proportion than that of an ape. About 92 per cent of human beings are right-handed, but apes tend to use both hands with equal ease.
The human hand can be used to grip objects in several different positions. These different positions require different types of grip strength which are typically quantified based on the way the hand is being used.
The crush grip is what is most commonly thought of as “grip”. It involves a handshake-type grip, where the object being gripped rests firmly against the palm and all fingers. A strong crush grip is useful in bone-crushing handshakes or for breaking objects with pressure.
In a pinch grip, the fingers are on one side of an object, and the thumb is on the other. Typically, an object lifted in a pinch grip does not touch the palm. This is generally considered a weaker grip position. The pinch grip is used when grabbing something like a weight plate or lifting a sheet of plywood by the top edge. Care must be taken to avoid cramping the muscles in the hand.
A support grip typically involves holding something, such as the handle of a bucket, for a long time. This type of strength is epitomized by the “Farmer’s walk”, where the bucket is filled with sand or water, and carried over a long distance. A great deal of muscular endurance is necessary to have a good carrying grip.
There has been extensive medical and ergonomic research looking at grip strength. This has led to the generation of normative data. The average for grip strength in Males is higher than that of Females. Averages also exist for different types of grip in different positions.
Grip strength increases or decreases depending on the arm position at which the grip strength is being measured. A person’s grip strength usually results in having the strongest grip strength when their arm is extended at 90° before their body, as opposed to the other extreme arm positions, rested at one’s side or held straight up above one’s head. Grip strength is not optimal if one’s arm is extended backwards beyond the resting position at the body’s sides. We can conclude that grip strength is affected via the different arm muscles and their ability to contract.