During a shoulder press up, the main joints that move are the shoulder joint (glenohumeral joint) and the elbow joint. The glenohumeral joint, which connects the upper arm bone to the shoulder blade, is a ball-and-socket joint, and the elbow joint, which links the upper and lower arm bones, is a hinge joint. Also, the scapulothoracic joint, which is where the shoulder blade meets the rib cage, moves to help the glenohumeral joint move.
A shoulder press up, also known as a shoulder press or military press, is an upper body exercise that primarily targets the shoulder muscles. During this exercise, several joints move to facilitate the lifting and lowering of the weight. These joints include:
Glenohumeral joint: This is the main joint involved in the shoulder press up. It is a ball-and-socket joint formed between the head of the humerus (upper arm bone) and the glenoid cavity of the scapula (shoulder blade). The glenohumeral joint allows for the shoulder's wide range of motion, including flexion, extension, abduction, adduction, internal rotation, and external rotation. During the shoulder press up, the glenohumeral joint goes through shoulder flexion (lifting the weight) and shoulder extension (lowering the weight).
Scapulothoracic joint: This joint is formed by the interaction between the scapula and the rib cage. During the shoulder press up, the scapulae move through elevation (lifting the weight) and depression (lowering the weight). This movement is essential for stabilizing the shoulder joint and ensuring proper movement of the arm.
Elbow joint: The elbow joint is a hinge joint formed between the humerus and the radius and ulna (lower arm bones). During the shoulder press up, the elbow joint goes through extension (straightening the arm as the weight is lifted) and flexion (bending the arm as the weight is lowered).
Wrist joint: The wrist joint, or radiocarpal joint, is formed by the radius (one of the two lower arm bones) and the proximal row of carpal bones in the wrist. Although not a primary mover in the shoulder press up, the wrist joint may experience some movement as it stabilizes the weight and maintains a neutral position.
Proper form and technique are crucial during the shoulder press up to avoid injury and maximize the exercise's effectiveness. Be sure to consult with a fitness professional if you're new to this exercise or have any concerns about your form.
Would like to add to all of the great / spot on! answers above !
When in a seated, fixed, isolation type position performing overhead presses, it is highly advisable ( and to avoid ) never to twist or lift the head off of the back pad, never raise the chin, or the head, never twist the neck or back at any point, while lifting, or lowering a bar, dumbbells or movement arm of an exercise machine. 'Train, don't strain!' Use strict form, by moving slowing, using a 5 X 5 second of lifting and lowering (concentric and eccentric movements) of any weight while in control of what you can comfortably handle, and by NEVER 'throwing' of forcing any weight in any or from or to any position. (The last repetition is usually the safest, but only when using great form of movement.)
Bad from can cause injury, and slower speed of movement will greatly reduce chance of injury, while at the same time increasing the simulation of more muscle fibers deeper within the fibrils.
A recommended number of repetitions is between 8 & 12 repetitions, or until volitional fatigue. Once you have perfected 12 repetitions without stopping, then and only then should you add between 5 & 10% more weight for the next session. Remember, more, is not necessarily better, and is usually _unnecessary! Focus on the minimum amount required to achieve enough stimulus, instead of a maximum amount. The results (muscle growth, stamina and strength) come later, during rest! Doing or using more, can impeded your recovery ability and time.
While standing, it is natural for the chin to be moved out of the way, but it should be minimized in it's movement towards the chest. Raising a bar from behind the head, may cause impingement of the humorous or parts thereof, but very light weight with low repetitions and low volume could be utilized only if shoulders are healthy , otherwise lifting from behind the neck or head may exacerbate any pending issues. If pain or weakness is already present, do not attempt this or any exercise and seek rehabilitation from a physical therapist. Gradual building with lower weights, bands or tubing is advised, from lifting behind the head and even in front as a starting point. Also, while gripping a machine handle or bar, it is advised that the elbows should be more aft, or in front the body, (frontal plane) and not too far out to the sides or behind the shoulders when lifting overhead. especially when a full range of motion is used. Frontal plane movements will reduce the possibility of impingements during overhead pressing movements.