Rowing is a low impact activity with movement only in defined ranges, so twist and sprain injuries are rare. However, the repetitive rowing action can put strain on knee joints, the spine and the tendons of the forearm, and inflammation of these are the most common rowing injuries. If one rows with poor technique, especially rowing with a curved rather than straight back, other injuries may surface, including back pains. Blisters occur for almost all beginner rowers as every stroke puts pressure on the hands, though rowing frequently tends to harden hands and generate protective calluses. Holding the oars too tightly or making adjustments to technique may cause recurring or new blisters.