Differentiate the primary muscle contraction types (concentric, eccentric, isometric) that dominate the execution of the Mat Push Up during the lowering phase versus the holding phase of the plank.

Muscle contractions are fundamental to movement and stability, categorizing how muscles generate force. A concentric contraction occurs when a muscle shortens under tension, generating force to overcome a resistance, such as lifting a weight or pushing against an object. An eccentric contraction occurs when a muscle lengthens under tension, controlling movement against a resistance, effectively braking or lowering a load. An isometric contraction occurs when a muscle generates force without changing its length, holding a position against a resistance. During the lowering phase of the Mat Push Up, the primary muscle contraction type that dominates is eccentric. As the body descends towards the floor, muscles such as the pectoralis major (chest muscle), triceps brachii (back of the upper arm), and anterior deltoid (front of the shoulder) are actively lengthening under tension to control the downward movement against gravity. These muscles are not shortening to pull the body up but are extending in a controlled manner to resist the pull of gravity and prevent a collapse. Conversely, during the holding phase of the plank, the primary muscle contraction type that dominates is isometric. In a plank, the body maintains a rigid, static position, typically in a straight line from head to heels, against the force of gravity. Muscles across the entire body, including the rectus abdominis and obliques (front and side abdominal muscles), erector spinae (back muscles), glutes (buttocks muscles), quadriceps (front thigh muscles), and shoulder stabilizers (such as the deltoids and triceps), are all generating continuous tension without undergoing any change in length. This sustained tension is what allows the body to hold the static posture without movement.