Chin-up
The chin-up (also known as a chin) is a strength training exercise designed to strengthen the latissimus dorsi muscle.

# Form
A chin-up has a specific form.  The movement begins with the arms extended above the head, gripping a fixed chin-up bar (or bar attached to a pulley in the case of the similar pulldown exercise, with the palms facing away from the exerciser) with a supinated grip (palms facing the exerciser).  The body is pulled up, or weight pulled down, until the bar approaches or touches the upper chest.  The weight is lowered until the arms are straight, and the exercise is generally repeated.
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  because of the natural tendency to do most of the work with the biceps rather than the lats. Initiating the pull with the shoulder blades helps avoid this problem.  The exercise is most effective when the body is lowered down to a full extension.
Chin-ups are often incorrectly referred to as pull-ups. The term pull-up is traditionally used when the exercise is performed with a pronated grip.

# Muscles targeted
Chin-ups target the latissimus dorsi muscle, assisted by the brachialis, brachioradialis, biceps brachii , teres major, posterior deltoid, infraspinatus, teres minor, rhomboids, levator scapulae, middle and lower trapezius and pectoralis muscles.  Chin-ups are thought to build width and thickness to one's back, as well as to promote growth of the biceps, brachialis, brachioradialis and pronator teres.

# Variations
- Sternal chinups  this variant employs a full range of motion, raising the sternum to the bar. The elbows are nearly directly below the shoulders this way.
- Towel chin-ups  a towel is looped over the bar, and instead of the bar, the towel is gripped.
- Weighted chin-ups  weight is added with 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 handed chin-ups  one hand grips the bar; the other hand holds the wrist/forearm of the gripping hand. It stresses the grip equally to a one-arm chin-up, but lessens the amount of work the biceps and lat of the gripping arm have to do compared to it.
- One forearmed chin-ups  one hand grips the bar; the other hand holds the upper arm of the gripping hand between the elbow and shoulder. It stresses the grip and bicep equally to a one-arm chin-up, but lessens the amount of work the lat of the gripping arm has to do compared to it.
- One arm chin-ups  one hand grips the bar; the other hand does not assist with the pull, it cannot touch the other arm.
- Drop chin-ups  the grip is released at the top of the movement, and the bar caught towards the bottom of the movement, to incorporate a slight drop.  This variant is for advanced athletes only.
- Supine chin-ups  in the supine position (with the feet initially supported), the arms are held perpendicular to the body as the grip the bar; the chest is pulled towards the bar instead of the chin. 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 often considered a type of row.

# Exercises that help
A useful exercise for beginners is the negative chin-up, where one is assisted to the top position and executes a slow, controlled descent. This is useful for those not strong enough to perform a concentric chin-up, and can also be used to keep training at the same weight when one is too exhausted to continue performing the concentric portion of the exercise.
Beginners who are not strong enough to perform a chin-up may make use of an assisted chin-up machine, where one stands on a bar with a counterweight to reduce the weight that one pulls up. These machines frequently also include a dip bar, allowing for assisted dipping. This keeps the exercise a closed-chain movement.
Another machine, which is open-chain (the person remains stationary, the resistance moves) which mimics the movement and is also helpful to training is the lat pulldown. Unlike the counterweight machine, the lat pulldown can provide as much or more resistance as a normal chin-up or pull-up through use of a counterweight stack. The lifter locks a pad into place above their thighs (near to the hip) to prevent them from rising off the ground when the resistance provided by the counter-weight (lifted through a pulley mechanism) goes beyond their body's.