Final answer:
The essential requirement for strengthening the lumbar extensors is controlled, progressive resistance, which involves a gradual increase in the resistance to build strength in the muscles of the back.
Step-by-step explanation:
A key requirement for strengthening the lumbar extensors is C) Controlled, progressive resistance. This method involves gradually increasing the resistance or weight used in exercises, allowing the muscles including the erector spinae group, which is primarily responsible for extending the vertebral column, to adapt and strengthen over time. This helps maintain good posture and supports the spine, particularly the lumbar curve, while carrying out daily activities and avoiding back strain.
It is important to note that while the other options, such as consistent body posture, dynamic weight training, and isometric exercises, are beneficial in their own right, controlled, progressive resistance is widely recognized for its effectiveness in strengthening the back muscles and improving muscle endurance.