Hill Sprint: Duration
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Short sprints of five to 15 seconds develop speed and power. Sprints of between 20 and 30 seconds improve fatigue resistance. Sprints longer than 30 seconds can improve your fitness, as they did for Agassi, but shorter sprints work your anaerobic system better. "The point is to get benefits you're not already getting from slow-steady cardio," says Snideman.