Decreasing speed of waves as water becomes shallow has dramatic consequences on the beach. As the waves slow, their profile (Figure on right) is laterally compressed and since each wave must carry the same energy it becomes higher. As the wave approaches shore this process continues until the height exceeds 1/7 th the wave length and the wave becomes unstable. Then the wave breaks.
Rowing is a low impact sport 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 rowers, especially in the beginning of one's rowing career, 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, as it is common to feather the blade (previously described). Another common injury is getting "track bites", thin cuts on the back of one's calf or thigh caused by contact with the seat tracks at either end of the stroke.