Triceps Lateral Heads

The triceps brachii is a major muscle located at the back of the upper arm, responsible for elbow extension. It consists of three heads: the long, lateral, and medial head. Together, these heads work during various activities, making the triceps essential for pushing movements and overall upper body strength. One study has shown an activation rate of up to 48% for the tricep brachii during the diamond pushup.

The triceps lateral heads are the outer portion of the triceps brachii. They originate at the humerus (upper arm bone) and insert into the ulna (one of the forearm bones). The lateral heads primarily extend the elbows.

Triceps Medial Heads

The triceps medial heads also originate from the humerus, below the lateral heads, and insert into the ulna. They are active during both resistance and non-resistance movements. They work in conjunction with the lateral heads to extend the elbows.

It is essential for the proper form and stability of the upper body during the lowering phase of the knee diamond pushup. This is the most active of the three heads of the tricep during the knee diamond pushup. In fact, its primary activation is during shoulder flexion at 90 degrees.

Triceps Long Heads

The triceps long heads sit above the medial heads and beside the lateral heads. They originate at the scapula (shoulder blade) and insert into the ulna. With this trajectory, they work to extend the elbow as well as stabilize the shoulder joint.

They are most engaged during overhead pressing movements due to the dual function of elbow extension and shoulder stability.

Sternal Head Of Pectoralis Major

The knee diamond push-up effectively activates the sternal head of the pectoralis major, primarily due to the hand positioning. The pectoralis major is a fan-shaped muscle on the anterior chest wall that comprises three heads. The sternal head originates from the sternum and attaches to the humerus.

Its primary function is to adduct (bringing the arm closer to the body), internally rotate, and flex the arm. It is most active during pushing movements and works as a stabilizer in the knee diamond pushup.

Abdominal Head of Pectoralis Major

The abdominal head of the pectoralis major originates from the external oblique and inserts into the humerus. Its primary muscle function is internal rotation and adduction of the arm. This is the lower portion of the pectoralis major.

Anterior Deltoid

The anterior deltoid sits on the front of the shoulder. It is responsible for shoulder flexion, abduction (moving the arm away from the body), and internal rotation. The anterior deltoid plays a role in stabilizing the shoulder during the knee diamond push-up.

Research shows that this muscle is recruited about 29% during the exercise. Variations in push-up styles significantly impact the activation of the anterior deltoid, with narrower grips leading to increased engagement.

Upper Rectus Abdominis

The rectus abdominis runs from the xiphoid process (bottom of the breastbone) to the pubic bone. It is often referred to as the six-pack. Its primary function is to flex the spine, compress the abdomen, and stabilize the core. It is further broken down into the upper and lower rectus abdominis.

The knee diamond push-up also engages the upper rectus abdominis for core stabilization. During a floor push-up, the entire rectus abdominis activates to more than 20% isometrically (muscle activation without movement). This engagement is crucial for maintaining proper form and stability throughout the movement. It makes the knee diamond push-up an effective choice for improving core strength, in addition to upper body training.

Lower Rectus Abdominis

The lower portion of the rectus abdominis is a crucial part of core and lower back stability. Due to its location, it assists in the proper pelvic positioning during bodyweight exercises to limit excess curvature of the lumbar spine.

While the upper rectus abdominis has muscle fibers running vertically, the lower rectus abdominis has muscle fibers running horizontally. This allows the muscles to work together to stabilize the spine and maintain proper form during the knee diamond pushup.

Erector Spinae

The erector spinae muscle group is activated in spinal stability and posture during exercises like the knee diamond pushup. It is important for the protection and stability of the lumbar spine. It runs from the pelvis to the ribs and neck in three different muscle groups. The three groups are the iliocostalis, longissimus, and spinalis.

The muscles work as a group to extend and sidebend the spine when performing movement, or to give stability when contracted isometrically. The knee diamond pushup, similar to floor pushups, recruits stability through this muscle group.

Studies show that activation in this muscle group varies with different types of pushups. In a floor pushup, the activation rate is 2%. A lower activation rate in this muscle group allows for lower back stability without too much compression for optimal safety.

Wrist Flexors

The wrist flexors are made up of the flexor carpi radialis, flexor carpi ulnaris, and palmaris longus. Each of these muscles originates a the elbow and inserts into the palm side of the wrist. They are engaged isometrically in conjunction with the wrist extensors during pushups to provide wrist stability.

Wrist Extensors

The wrist extensors are made up of the extensor carpi radialis longus, extensor carpi radialis brevis, and the extensor carpi ulnaris. They work together on the dorsal (back) aspect of the forearm to extend the wrist.