A marathoner's concern includes PACE, PACING, EXHAUSTION, CRAMP, STRIDE, and BLISTER. PACE is the speed at which a runner moves, while PACING is the act of controlling one's speed during a race. EXHAUSTION is the feeling of being extremely tired, often caused by physical exertion. CRAMP is a sudden, involuntary muscle contraction that can cause pain and discomfort. STRIDE is the length of a single step taken while running. BLISTER is a raised area of skin filled with fluid, usually caused by friction or pressure.