Final answer:
The first-class lever in the human body is the glenohumeral joint.
Step-by-step explanation:
The first-class lever is a type of lever in which the fulcrum is located between the effort and the load. In the human body, one example of a first-class lever is the glenohumeral joint, which is the joint that connects the upper arm bone (humerus) to the shoulder blade (scapula). In this joint, the fulcrum is the shoulder joint itself, the effort is produced by the muscles attached to the humerus, and the load is the weight or resistance being lifted by the arm.