Historians generally agree that human interest in fitness and physical activity can be traced back to the earliest civilizations. From ancient societies, such as those in Mesopotamia, Egypt, Greece, and Rome, people engaged in physical training for purposes such as warfare, agriculture, and overall health.
The ancient Greeks are particularly noted for their emphasis on physical fitness, culminating in the establishment of the Olympic Games in 776 BCE, which celebrated athletic prowess.
Therefore, the most accurate answer to your question would be "ever since the beginning of civilization."