The chin-up (also known as a chin/chinup) is a strength training exercise. People frequently do this exercise with the intention of strengthening muscles such as the latissimus dorsi and biceps, which extend the shoulder and flex the elbow, respectively.
It is a form of pull-up in which the range of motion is established in relation to a person's chin.
A chin up is named by bringing the chin up through space, specifically in relation to its position with the bar or other hand grips. This can be either touching the bar (more easily done by extending the neck, though that could be considered cheating) or by bringing the chin over the bar.
This is usually achieved most easily with vertical forearms that are close to the body. For most, bringing the chin this high is most easily achieved with a supinated (underhanded, palms-toward) grip. Due to this, the phrase "chin up" has become associated with pulling with this type of grip. Some have delegated the term pull-up to refer to the pronated (overhanded, palms-away) grip. In spite of this, many refer to pull-ups with a pronated grip also as chin-ups, and the supine grip is still regularly called a pull-up.
Some organizations such as the American Council on Exercise have adopted this new terminology, issuing statements such as: "a chin-up differs from a pull-up in that the puller's hands are facing towards him or her in a chin-up, and away in a pull-up." Organizations such as the United States Marine Corps however, use the term pull-up interchangeably to refer to both the overhand and underhand grips.
The body is pulled up, with the bar approaches or touches the upper chest. A chin-up is considered complete based on a variety of criteria in relation to where the chin should be in respect to the bar, or in respect to the hand grips.
The body is then lowered until the arms are straight, and the exercise is generally repeated.
Like any pull-up, chin-ups can be performed with a kip, where the legs and back impart momentum to aid the exercise, or from a dead hang, where the body is kept still. Performing the chin-up correctly can be tricky with a supinated grip, because of the natural tendency to do most of the work with the elbow flexors (largely biceps) rather than the shoulder extensors (largely lats).
Initiating the pulling action with scapular depression may help avoid this problem. The exercise is most effective in stretching the working muscles when the body is lowered down to a full extension.
Grip and thumb position 
A closed grip involves the thumb on the opposite side of the bar from the rest of the fingers. In this position, the forearms are using extra muscles to hold the puller up on the bar.
Muscles targeted 
Chin-ups, like most pull-ups, target the latissimus dorsi muscle as a shoulder extensor, scapular downward rotator and scapular depressor, in bringing the spine to the humerus. This is assisted by elbow flexors (brachialis, brachioradialis, biceps brachii) which bring the humerus to the forearm.
The lat's functions are also assisted, both by shoulder extensors (teres major, posterior deltoid, infraspinatus, teres minor), scapular downward rotators (rhomboids, levator scapulae), and scapular depressors (lower trapezius and pectoralis muscles).
Pulling higher with a narrow grip puts the focus on extension rather than adduction of the shoulder.
If one leans back at the top of the movement, the focus is shifted somewhat towards scapular retraction and hyperextension.
The weight of the legs and pelvis are born by spinal ligaments and various muscles that flex or extend the spine. If the pelvis is tilted anterior and the legs brought behind, the erector spinae (with aid from the lats) bears more weight. If the pelvis is tilted posterior and the legs brought in front, the rectus abdominis (with aid from the psoas) bears more.
- Sternal chinups — this variant employs a fuller range of motion at the top, raising beyond the chin and touching the sternum to the bar. The elbows are nearly directly below the shoulders this way. This requires adequate scapular depression. If leaning back (arching the spine) a sternum-up can be done that is not a chin-up, this shifts to requiring scapular retraction.
- Weighted chin-ups — weight is added dangling from a dipping belt or via weighted belt or vest, ankle weights, chains, medicine ball between the knees, dumbbell between the feet or kettlebells on top of the feet.
- One arm chin-ups — one hand grips the bar and the other hand does not assist
- One hand chin-ups — One hand grips the bar while the other arm assists by grabbing the forearm of the arm hanging onto the bar. These require far less strength than a One arm chin-up.
- Supine chin-ups — in the supine position, the arms are held perpendicular to the body as the grip the bar; instead of the chin, the chest is pulled towards the bar. This exercise is performed in the horizontal (transverse) plane, whereas other chin-up variations are performed in the vertical (coronal) plane. As a result, this variation recruits the trapezius and teres major muscles much more than a vertical chin-up would, and is more commonly known as the supine row. Advanced versions popular amongst gymnasts are performed completely off the ground in some type of front lever.
- Harrison chin-ups — a term coined by powerlifter Dan Harrison, this technique is similar to a normal chin-up but with an arched spine to more effectively target the latissimus dorsi and take strain off the biceps. Though it has become a recent phenomenon on the west coast of the United States (especially with beach-goers) it has not yet gained widespread popularity.
Training and performance 
Specific training is needed in order to increase chin-ups performance.
The performance can be measured in various ways:
- number of repetitions without touching the floor
- number of repetitions in a specified time interval (1/3/30 minutes, 1/6/12/24 hours)
- number of repetitions with a total weight (body weight plus additional weight)
Various organizations like Guinness World Records maintain lists of world records for chin-ups and pull-ups. Both recordholders.org and Guinness World Records maintain that Pull-ups use a pronated grip while Chin-ups use a Supinated Grip
- "Chin-up". acefitness.org. American Council on Exercise. Retrieved 27 March 2011.
- USMC fitness PDF Chapter 2: "a command will not mandate that Marines must use the overhand grip when executing pull-ups or flexed-arm hang" - May 10, 2002
- exrx.net defines Chin-Up, does not mention a supinated grip and illustrates it with a pronated grip.
- Types of chin-ups bars for home gyms
- Video demonstration of a chin-up
- World Records for Chin-Ups and Pull-Ups
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