In a movie, back in the Roman Empire, or the Egypt Empire, labors were carrying stones on their head. Some pulling the cart loaded with heavy stones. There are a supervisors, royal guards, whipping them to move faster.
This is one of the very outdated safety law in Thailand that restrict the weight that each of the labor can carry. It is purely based on gender and age of the labor. Not thing related to ergonomic or manual handling safety things.
