You may have seen a treadmill before, but have you ever seen a swimming pool where the water continuously flows, allowing you to swim in place? This is called a countercurrent pool, also known as an endless pool, and it is a training tool used by many professional swimmers. But here's the question: Since athletes already have access to standard swimming pools, why go through the trouble of building such a complex and power-consuming facility? Is it just to improve endurance or explosive strength? But for that purpose, can't they just strap on weights and swim in a regular pool? That sounds cheaper and more convenient. In fact, a countercurrent pool does more than just increase training intensity; it has many other benefits. One of its main advantages is that it can simulate various water conditions, from calm rivers to rough ocean waves. More importantly, it has powerful visualization features. Coaches can stand by the pool and, through the clear glass walls, observe and analyze the swimmer's technique and body position in real time. It's like having a fully controlled, high-tech training environment, perfect for fine-tuning every detail.