Recently I’ve been asked frequently about pull ups, so heres a somewhat detailed description:
The chin-up / pull up is a popular multi-joint, closed & discrete skill exercise and it can be performed in a variety of ways. However it is performed, this skill has a very distinct start and finish. This exercise is always performed in a predictable environment and performed with either a pronated or supinated grasp and with a narrow or a wide grip. The width of the grip and the pronation or supination of the hands will determine what muscles will be affected & exercised during this strenuous muscular activity.
The overall performance objective of the chin-up is to increase muscle strength. One of the main reasons for this exercise’s popularity is due to the fact that this particular exercise works a plethora of upper body muscles. Almost every muscle in the arms, shoulders, back, and chest are repeatedly contracted concentrically and eccentrically while this action is performed. “Chin-ups are an excellent way to improve upper body strength” (Chin ups).
A chin-up isn’t an exercise that a novice should jump right into, or begin doing without assistance. It is a very strenuous activity and can cause a number of injuries to the shoulder and elbow joints. Muscle can become strained, pulled, and even torn. Typically, the most common injuries occur in the elbow or rotator cuff. Which explains why starting out, the subject training should do assisted pull-ups until they build up enough strength in their upper body muscles and joints to perform this exercise on their own. This type of body/weight lifting puts a great deal of strain on the shoulder and elbow joints.
Simply explained, this exercise can be described by a subject grasping an elevated horizontal bar, hanging from it and pulling up until their chin is over the bar. By grabbing the bar the subject creates the base of support with his hands and the bar. Along with creating the base of support the line of gravity is also determined. This is a stable movement due to the fact that the line of support goes directly through the base of support during both phases of the exercise.
There are two phases to this activity, the pulling or up phase and the lowering or down phase. The up phase is when the weight is lifted (pulled up) and the down phase is when the weight is lowered. During the pulling up phase, one is striving to reach the “chinning position” or complete “pull up” position, by getting their chin above the bar (Figure 1: Right). The pulling up motion forces the muscles involved to contract concentrically. The lowering stage involves the process of the subject slowly dropping or lowering themselves back into their beginning position (Figure 1: Left). As the subject lowers himself or herself the muscles are contracted eccentrically. Almost every muscle involved stays contracted in one way or another while hanging from the bar.
The starting position is initiated by standing under the bar that the exerciser intends to use to pull their body up. Typically, the bar is at a height that is just out of ones reach and will require the subject to jump up to grasp the bar. Before jumping to grab the bar, one must choose their type of grip, whether it is a wide, narrow, overhand (pronated), or an underhand (supinated) grasp. One must also keep in mind that when doing a pull-up the style of their grip among other things will determine what muscle groups and joints are affected. The palms facing towards the body (supinated) grip will place more of an emphasis on the bicep muscles of the upper arm and the palms facing away (pronated) grasp will focus mostly on the back muscles. As soon as a grip is chosen, one is ready to begin this exercise.
Figure 1: Left Panel: Beginning position (supinated grip); Center Panel: Pull-up position (supinated grip) (Poliquin); Right Panel: Pull-up position (pronated grip) (Exercise).
As seen in the pictures, the center of gravity (C.O.G), or balance point generally stays the same. It mostly stays in its point of origin, in the pelvis region, in front of the sacrum. In women the C.O.G. is going to be just a little bit lower. During the up and down phases of this skill this balance point will move up ever so slightly. In the up phase or chinning position it will move upward, because the elbows are flexed and some body mass is being elevated above anatomical position. In the hanging or down phase, it will be a few inches higher than normal, due to the fact that the arms are completely extended above the subject’s head.
Once the subject has grabbed the bar, their feet should not be able to touch the floor (Figure 1: Left). Then the exerciser should pull their body up until their chin is about or just above the level of the line of their hands on the bar (Figure 1: Right). The next step is lowering your body down to a full stretch. Repeat these motions without touching the floor to form repetitions.
There are two main joints/levers in motion when performing a chin-up: the shoulder and the elbow. During the up phase, both joints experience the same type of isotonic muscle contraction, no matter how the horizontal bar is gripped. The muscles shortening in length describe this type of contraction, known as a concentric contraction. The lowering phase, experiences the opposite type of isotonic contraction, the eccentric contraction, where the muscles lengthen. Both levers are considered third class levers and are at a mechanical disadvantage. The fulcrums of these levers are at the elbow & shoulder joints. For both levers, the resistance comes from the exercisers body weight and the resistance is cause by the tensing of the muscles trying to lift the subject’s body upward.
The shoulder joint receives a large benefit from this workout, due to the variety of muscles that come into play during the up & down motion (Figure 2). For example, a chin-up will build the pectoralis major, deltoid, latissimus dorsi, teres major, subscapularis, infraspinatus, teres minor, triceps, and wrist & hand flexor muscles simultaneously. All of these muscles work together to keep the hands and shoulders in place while the exerciser hangs from the pull-up bar.
Figure 2: Joint actions: Muscle Analysis – Narrow Grip Chin Up (up phase) (Exercise).
Joint : Shoulder Joint
Muscle Group: Shoulder Joint Adductors
Specific Muscles:Pectoralis Major, Deltoid, Latissimus Dorsi, Teres Major, Subscapularis, Infraspinatus, Teres Minor, Triceps
Joint: Shoulder Girdle
Action: Adduction and Downward Rotation
Muscle Group: Shoulder Girdle Adductors and Downward Rotators
Specific Muscles: Trapezius, Rhomboid, Pectoralis Minor
Joint: Elbow Joint
Action: Elbow Flexion
Muscle Group: Elbow Flexors
Specific Muscles: Biceps Brachii, Brachialis, Brachioradialis, Pronator Teres
*The same specific muscles will be recruited in an eccentric contraction in the down phase of this exercise.
The chin-up skill mainly takes place in the frontal plane and along the longitudinal axis. Only when or if the person performing the chin-up swings on the bar will they be touching into the sagittal plane and moving on the anteroposterior axis. If performed precisely, the exerciser will only move upward & downward, not forward or backward.
Many muscles stabilize the body during a pull-up. Hand and wrist flexor muscles play a small, but important role in contributing to this exercise. They experience flexion during both the up and down phases of a chin-up. The muscles of the hand and wrist contract isometrically (muscle stay the same length), to keep a steady grasp on the horizontal bar. By keeping the hand & wrist muscles contracted the exerciser will also strengthen their grip and forearm muscles. Additionally, abdominal muscles receive a beneficial workout due to the stabilization needed throughout the entire core.
Throughout this strenuous activity/skill the moment of inertia generally doesn’t change; this is mainly due to the fact that it is done in such a controlled & predictable environment and the body stays mostly in one position. No matter what axis it is viewed from (anteroposteriol, medial lateral, longitudinal), the body stays in generally the same position. The only way the moment of inertia would change is if the person doing the chin-up swung from the bar or curled up their body.
Impulse and changes in momentum are generated through all points in both phases of this skill. When pulling up the momentum is slowly being created upward by the contraction of the muscles and when lowering it is changing directions and being controlled by an eccentric contraction. The impulse is caused by the firing of the muscle fibers.
Chin-ups are “known as one of the most difficult exercises” (Furey) and have often led people to “throw in the towel.” It takes a lot of inner and outer strength to perform this exercise. Without question chin-ups “are one of the most beneficial overall muscle and strength developers” (Furey).
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