Push-Up Mechanics: Joint Actions and Muscles in the Concentric Phase

What joint actions occur during the concentric phase of a push up?

During the concentric (pushing up) phase of a push-up, the primary joint actions are shoulder horizontal adduction, elbow extension, and scapular protraction. These coordinated movements enable the body to move away from the ground against gravity.

Understanding the Push-Up: A Primer

The push-up is a foundational, compound exercise revered for its effectiveness in developing upper body pushing strength, core stability, and overall muscular endurance. As a closed-kinetic chain movement, it involves multiple joints and muscle groups working synergistically. To truly master and optimize this exercise, it's crucial to understand the specific anatomical movements occurring at each phase.

The Concentric Phase Defined

In exercise science, muscle contractions are typically categorized into three types: isometric (no change in muscle length), eccentric (muscle lengthens under tension), and concentric (muscle shortens while producing force). The concentric phase of an exercise is the "lifting" or "pushing" portion, where the muscles overcome the resistance to move the body or an object.

For the push-up, the concentric phase begins from the bottom position, with the chest near the floor, and involves actively pushing the body upwards until the arms are fully extended (or nearly so), returning to the starting plank position. This is the "work" phase where the primary movers are actively shortening.

Key Joint Actions During the Concentric Push-Up

The push-up is a multi-joint movement, meaning several joints move simultaneously to complete the action. During the concentric phase, the three primary joints undergoing significant action are the shoulder (glenohumeral joint), the elbow, and the scapulothoracic joint.

• Shoulder Joint (Glenohumeral Joint): Horizontal Adduction

  • Action: As you push up, your humerus (upper arm bone) moves from an abducted and slightly extended position towards the midline of your body, often described as "closing the gap" between your upper arm and torso. This movement is known as horizontal adduction (or transverse adduction).
  • Muscles Involved: The primary muscles responsible for this action are the Pectoralis Major (chest muscle) and the Anterior Deltoid (front of the shoulder). The Pectoralis Major, particularly its sternal head, is a powerful horizontal adductor.

• Elbow Joint: Extension

  • Action: Simultaneously with shoulder movement, the angle at your elbow joint increases as your forearm straightens relative to your upper arm. This is called elbow extension.
  • Muscles Involved: The primary muscle group executing elbow extension is the Triceps Brachii, located on the back of your upper arm. All three heads of the triceps are powerfully engaged in this phase.

• Scapulothoracic Joint: Protraction

  • Action: While not a true anatomical joint in the same way as the shoulder or elbow (it's a physiological articulation between the scapula and the rib cage), the movement of the scapula (shoulder blade) is critical. During the final portion of the concentric push-up, especially as you reach full arm extension, the scapulae move away from the spine and wrap around the rib cage. This action is known as protraction.
  • Muscles Involved: The Serratus Anterior is the primary muscle responsible for scapular protraction. This muscle is vital for stabilizing the scapula against the rib cage and allowing for efficient force transfer from the chest and triceps to the hands. Weakness in the serratus anterior can lead to "winging" of the scapula and compromise push-up mechanics.

Primary Muscles Involved

To summarize, the key muscles driving the concentric phase of the push-up, corresponding to the joint actions described, include:

• Pectoralis Major: Primarily responsible for shoulder horizontal adduction.
• Anterior Deltoid: Assists the pectoralis major in shoulder horizontal adduction and contributes to shoulder flexion.
• Triceps Brachii: The main mover for elbow extension.
• Serratus Anterior: Crucial for scapular protraction and stabilizing the scapula.
• Core Musculature (Rectus Abdominis, Obliques, Transverse Abdominis, Erector Spinae): While not directly involved in the pushing action, these muscles work isometrically to maintain a rigid plank position, preventing sagging of the hips or arching of the back, and ensuring efficient force transfer.

Biomechanical Considerations and Performance Tips

Understanding these joint actions and the muscles that drive them is fundamental for optimizing your push-up technique and preventing injury.

• Full Range of Motion: Ensure you achieve full elbow extension and a degree of scapular protraction at the top of the movement to fully engage the triceps and serratus anterior. Conversely, descend until your chest is close to the floor to maximize the stretch on the pectorals and anterior deltoids.
• Elbow Position: The angle of your elbows relative to your torso can shift the emphasis. Flaring elbows wide (90 degrees) places more stress on the shoulder joint, while tucking them closer (45 degrees) generally increases triceps involvement and can be safer for the shoulders.
• Core Engagement: Consciously brace your core throughout the movement. A stable torso provides a solid foundation for the upper body muscles to exert force efficiently.

Conclusion

The concentric phase of a push-up is a sophisticated display of coordinated muscular effort and joint mechanics. By understanding the specific actions of shoulder horizontal adduction, elbow extension, and scapular protraction, and the roles of the pectoralis major, anterior deltoid, triceps brachii, and serratus anterior, fitness enthusiasts and professionals alike can refine their technique, maximize muscle activation, and build a stronger, more resilient upper body. This foundational knowledge empowers you to perform the push-up not just as an exercise, but as a testament to intelligent movement.