Which of the following best describes a 2nd class lever in the human body?

A second-class lever in biomechanics is characterized by the load being positioned between the effort and the fulcrum. In the context of the human body, an ideal example of this is found in the calf raise. During a calf raise, the pivot point occurs at the ankle joint (the fulcrum), the effort is applied via the calf muscles (gastrocnemius and soleus) when you push off the ground, and the load is represented by the weight of the body acting downwards through the heel.

This lever system enables movement against gravity efficiently, allowing for greater force output with less effort. The mechanical advantage of second-class levers is that they allow a relatively small amount of muscle force to lift a greater load, which is essential in activities that involve lifting the body, such as standing on tiptoes or jumping.

In contrast, the other activities listed—such as a bicep curl, wrist flexion, and shoulder abduction—are examples of different classes of levers (primarily third-class levers), where the effort is applied closer to the fulcrum than the load, making them less efficient in terms of mechanical advantage compared to second-class levers.