Grip strength is the force applied by the hand to pull on or suspend from objects and is a specific part of hand strength. Optimum-sized objects permit the hand to wrap around a cylindrical shape with a diameter from one to three inches. Stair rails are an example of where shape and diameter are critical for proper grip in case of a fall. Other grip strengths that have been studied are the hammer and other hand tools. In applications of grip strength, the wrist must be in a neutral position to avoid developing cumulative trauma disorders (CTD's).
Grip strength is a general term also used by strength athletes, referring to the muscular power and force that they can generate with their hands. In athletics, it is critical for rock climbers and in competitions such as the World's Strongest Man. Grip strength training is also a major feature in martial arts, and can be useful in various professions where people must work with their hands.
Types of grip 
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 some applications, a type of roar may be emitted in an attempt to raise the chi and enhance the strength of the grip.
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.
Normative Data 
There has been extensive medical and ergonomic research looking at grip strength. This has led to the generation of normative data. Average values exist for both men and women. Averages also exist for different types of grip in different positions.
We find that grip strength either 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.
In medicine 
Grip strength is often used in medicine as a specific type of hand strength. The purpose of this testing is diverse, including to diagnose diseases, to evaluate and compare treatments, to document progression of muscle strength, and to provide feedback during the rehabilitation process as a measure indicating the level of hand function. For example, it is used to indicate changes in hand strength after hand surgery or after a rehabilitation program. By asking subjects to maintain a maximum contraction for longer periods, it can be used as a measure of fatigue. It is also able to predict a decline in function in old age. Since the above-mentioned grips involve the action of a large number of different joints and muscle groups, grip strength is not always very sensitive to measure individual muscle groups in medicine. For this purpose, dynamometers have been developed that provide more specific information on individual muscles in the hand such as the Rotterdam Intrinsic Hand Myometer (RIHM).
In sports 
Hand grip is an important, though often overlooked, component of strength in sports. However, the grip strength is most often a secondary or auxiliary function of the sport. Sports in which grip strength are included within the secondary focus include the following: movement-based climbing, gymnastics, horse racing, powerlifting or professional arm-wrestling; ball-based baseball, gridiron football, rugby, badminton or tennis; and combat sports such as brazilian jiu-jitsu, boxing, fencing, judo or wrestling.
As a separate discipline 
From their beginnings as odd performances at fairs and circuses, grip feats have recently gained acceptance as a sport in their own right, with competitions being held with increasing regularity. Events include one-arm deadlift, nail bending, the closing of torsion spring hand grippers, v-bar (vertical bar) lifting, and standardized pinch apparatuses. Other common events may include Rolling Thunder lifts, thickbar deadlifts, and "Blob" lifting.
The major contests are:
- World's Strongest Hands
- Champion of Champions
- European Grip Championships
- Mighty Mitts
- Britain's Strongest Hands
- British Grip Championships
- Münsterland Grip Challenge
- Global Grip Challenge
- Loddekopinge Grip Challenge
- Australian Grip Championships
- German Grip Championships
- Backyard Bastard Bash
- Metroflex Mayhem at Metroflex
Feats of Strength 
Although grip strength lends itself to impromptu performances that might feature a unique implement or cater to a particular individual or a small group, performances on standardized, widely available tests carry more weight. One such feat involving world class grip strength is officially closing a No. 3 Captains of Crush Gripper, first accomplished by Richard Sorin in 1991. Card tearing is a traditional feat of grip and lower arm strength that has a rich history, and top performances include John Brookfield tearing three decks of cards at once  and tearing 50 decks of cards in less than a minute. Brookfield has explained the technique for tearing cards in both his MILO article on the topic, and in his book The Grip Master's Manual
Training methods 
Grip strength training requires a different type of training regimen than other muscular training. The reasons are primarily based on the interplay of the tendons and muscles and the lack of "down time" or rest that most people's hands get.
It is generally considered that all aspects of the hand must be exercised to produce a healthy and strong hand. Only working on closing grip will cause an imbalance between closing and opening (antagonist) muscles, and can lead to problems such as tendinitis and carpal tunnel syndrome.
For closing grip 
- Thick bar and Thick Grip work on a two-inch or thicker bar—such as deadlifts, pullups, and the farmers walk—trains the support grip.
- Grippers train the crushing grip.
- Plate pinches grabbing plates smooth side out and pinching them.
- Sledgehammer lever — levering a sledgehammer using the wrists to train fingers and wrists.
- Plate curls/wrist curls — grabbing a plate and doing wrist curls or regular curls with them with the fingers on the bottom and thumb on top, trains the wrists and fingers and thumb for pinch grip.
- Blockweights — cut off ends of hex dumbbells that are grasped in a pinch grip fashion from different sides of the blockweight with one end grasped by fingers and other by thumb; trained with either singles, timed holds, or tosses from hand to hand.
For opening grip 
- Extensors; these are the muscles that oppose the flexors of the hands and should be trained to achieve a good balance between opposing muscle groups; extensor muscles are key in grip because they must contract aggressively to support finger flexion. Shoving your hand in something like rice and extending it, or placing something such as rocks in a coffee can, putting your hand in there, and extending it to pick up the coffee can, are ways of training your hand extensors.
- Some grip companies, such as IronMind Enterprises Inc., sell high-resistance rubber bands which work the extensor grip. Another option, is a weight based machine like "The Gripper" offered by Fitness Specialties U.S.A.. This type of plate loaded machine will not only strengthen your grip but also your forearm strength.
- As finger flexor/extensors serve a function as wrist flexor/extensors, doing wrist extension exercises (sometimes called "reverse wrist curls") would also stimulate the finger extensor fibers.
- Doing fist pushups on the backside of the first fingerbone would increasingly put pressure on the extensor muscles as weight was shifted from knuckle-end to the further joint. When in a tight first, the flat of the fingernails can dig into the palm and push the skin down to create a bridge to stabilize the first structure and prevent hyperflexion of the knuckle joints (which can be observed by doing pushups with the entire backside of the fingers flat on the ground, fingers pointing towards the opposite hand).
For stabilization 
- Fingertip pushups would utilize both opening and closing grip muscles to keep the finger from sliding, as well as more focused bone density in the hand, though they are very strenuous and dangerous unless approached progressively.
- Hand stands free from a wall with fingers pointing behind would use gripping stretching to stabilize the hand to prevent the body from falling towards the front, and extensor muscles to prevent the body from falling towards the back.
- Metal-rod exercises strengthen the grip indirectly but very effectively through strength training using a metal rod or pole.
Noted grip strength athletes 
- Mathiowetz V, Kashman N, Volland G, Weber K, Dowe M, Rogers S (February 1985). "Grip and pinch strength: normative data for adults". Arch Phys Med Rehabil 66 (2): 69–74. PMID 3970660.
- Effects of interface factors on the handgrip and pinchgrip force exertion capabilities, muscular contraction speed and endurance Winson W.S. LO, Alan H.S. CHAN, Michael K.H. LEUNG 
- Rantanen T, Guralnik JM, Foley D, et al (February 1999). "Midlife hand grip strength as a predictor of old age disability". JAMA 281 (6): 558–60. doi:10.1001/jama.281.6.558. PMID 10022113.
- Geere J, Chester R, Kale S, Jerosch-Herold C (2007). "Power grip, pinch grip, manual muscle testing or thenar atrophy – which should be assessed as a motor outcome after carpal tunnel decompression? A systematic review". BMC Musculoskelet Disord 8: 114. doi:10.1186/1471-2474-8-114. PMC 2213649. PMID 18028538.
- Willoughby, David P. The Super Athletes. A.S. Barnes and Company: 1970
- Brookfield, John. Card Tearing. "MILO: A Journal For Serious Strength Athletes," Volume 1, Number 4 (January 1994), pp. 25-26. IronMind Enterprises, Inc.: Nevada City, California
- Brookfield, John. The Grip Master's Manual. IronMind Enterprises, Inc.: Nevada City, California: 2002
- John Brookfield (2008). Mastery of Hand Strength, Revised Edition. Ironmind Enterprises. ISBN 978-0-926888-81-4.
- John Brookfield (2002). The Grip Master's Manual. Ironmind Enterprises. ISBN 0-926888-11-0.