I strained my lower bach. I realized it when I got up this morning. A sharp pain hit my left side of lower back. I frowned and slowly raised my body, and then tried to make sure when it hurt how I moved. I understood that it hurt when I placed my weight on left side. At first, I couldn't get why it occurred. But eventually, I reached one hypothesis. It might be due to the chair I had been sitting during learning English yesterday. The plate of the chair my hip touched on was very solid and the chair itself didn't stand vertically. It might add too much weight on my left lower back. Today, I avoided using the chair and the desk. I studied on the bed all day long.