Final answer:
During a push-up, the abdominals and erector spinae perform an isometric contraction, maintaining stability without significant change in muscle length.
Step-by-step explanation:
During the performance of a push-up, the muscles involved perform different types of contractions. The abdominals and erector spinae muscle groups maintain stability and assist in keeping the spine and pelvis aligned. This role is best described as an isometric contraction, where the muscle does not change in length significantly and the angle at the joints does not change, but muscle tension is increased to hold the body in a stable position.