The very first image that comes to mind when you think of a pull-up is quite possibly a chiseled physique wearing military fatigues. It is true that the military does use this exercise as one base for physical fitness, however, dont let that image scare you away. Pull-Ups can easily be defined as one of the best muscle and strength developers - and you can do them almost anywhere. Pull ups require you to lift your own body weight utilizing many muscles in the upper body. Many other exercises are done with ease after you have mastered the pull-up and strengthened your upper body.
A pull-up is a compound strength training pulling exercise where the body is suspended by extended arms utilizing an overhand (pronated) grip, holding a fixed bar, then pulled up until the elbows are bent and the head is higher than the hands. Compound exercises require many muscle groups to work together and include movements around two or more joints. Activities that we perform every day typically are made up from many compound movements.
The Muscles behind the Movement
Pull ups are a staple exercise of strength training for any athlete. They first require you to use the many muscles throughout the hand and forearm. This is a necessary foundation to reduce injury whether you use a computer all day or are outside doing manual labor. Biceps, triceps, and deltoids act as assisting muscles throughout the exercise while the latissimus dorsi and trapezius are the prime movers. Lets not forget about the core - abdominal muscles are engaged to stabilize your body during the movement. Stressing muscles in the upper body can actually decrease injury by increasing bone density and require the use of many stabilizers within the shoulder. The actual movement of the pull-up will also assist in maintaining proper range of motion throughout the upper body.
FOREARM - The structure between the elbow and wrist containing many muscles, including the flexors and extensors of the digits, brachioradialis (flexor of the elbow), and pronators and supinators that turn the palm of the hand upwards or down.
BICEPS - The biceps brachii (commonly referred to as "biceps"), the muscle located on the front of the upper arm, is responsible for the forearm rotation and elbow flexion.
TRICEPS - The triceps brachii (commonly referred to as "triceps"), the large muscle located on the back of the upper arm, is responsible for the action of straightening the arm.
*Due to the strength of the prime movers used, biceps and triceps typically act as dynamic stabilizers.
DELTOIDS - The deltoid muscle is responsible for the much-coveted curved contour of the shoulder and is made up of three sections: front, lateral, and rear. Pull ups, although not a major contributor to deltoid development (beside rear deltoid), are still an ancillary benefit to this muscle.
LATISSIMUS DORSI - The latissimus dorsi (meaning "broadest muscle in the back") is responsible for adduction, medially rotating, and extending the arm at the shoulder. It also plays a synergistic role in extending and laterally flexing the lumbar spine.
TRAPEZIUS - The trapezius is a large superficial muscle located between the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula. Its primary function is to move the scapulae and support the arm.
CORE - Area of the body referring to the rectus abdominis ("abs") and erector spinae. Full-body functional movements traditionally originate from this area of the body and it provides stabilization during many daily activities and posture.