What best describes a method of pushing against an immovable object?

The method of pushing against an immovable object is best described as isometric exercise. Isometric exercises involve muscle engagement where there is no visible movement in the joint angle, and the length of the muscle does not change despite the contraction. In this scenario, when pushing against an immovable object, the muscles are activated, generating tension without any movement occurring, thus qualifying the activity as an isometric exercise.

Dynamic stretching, on the other hand, involves moving parts of your body through a full range of motion, which does not apply to this scenario as it involves motion rather than maintaining position against resistance. Concentric contraction refers to muscle shortening while generating force, which is not the case when pushing against an immovable object. Finally, an extension exercise typically refers to actions that involve increasing the angle between body parts, and while it may involve muscle contraction, it is not specific to the scenario described.