Among the options provided, the correct answer is c) pushing against an immovable wall.
An isometric contraction occurs when a muscle generates force without changing its length. In this scenario, when you push against a wall that doesn’t move, your muscles are working hard to maintain the position and exert force, but there is no movement or length change. This contrasts with the other options:
- a) bending the elbow – This involves movement and is an example of a concentric contraction.
- b) rotating the arm – This also involves movement and is not isometric.
- d) nodding the head as to say yes – This motion involves muscle length changes and is not isometric.
- e) shaking the head as to say no – Similar to the previous example, this involves movement and therefore isn’t isometric.
Thus, pushing against an immovable object is the classic example of an isometric contraction, where the muscles exert force without creating movement.