Answer
The triceps brachii is one of the arm muscles. It has three origins ; the back of the humerus, the radial groove of the humerus ,and a tubercle below the glenoid fossa. It crosses the elbow joint and inserts on the olecranon process of the ulna.
In a push-up the triceps extends the elbow joint and straightens arm and forearm.
When the triceps is holding the upper limb in this position, the action is a demonstration of the first/order of levers. In the class the fulcrum (F) is between the resistance/load (R) and the effort/power (E) ---RFE.
Work Step by Step
The action of holding the upper limbs in position in a Push-Up posture, is an example of the working of the first class of levers. The triceps brachii applies the effort to the olecranon process; the elbow joint is the fulcrum; the weight of the body being applied to the arm and forearm is the resistance. The action of the triceps extends the elbow joint and aligns arm and forearm in a some straightened relationship. The representation of the first class of levers is RFE., fulcrum between effort and resistance.