mountain biker, mountain bicycle, mountain, mountain bike, prosthetic, prosthetics, rider, ride, bike, bike helmet, bike ride, down hill, extreme sport, extreme, adrenaline, sport, bicycle, epinephrine, liquid body substance, traveler, discipline, container, person, neurochemical, travel, life science, wheeled vehicle, vehicle, medicine, neurotransmitter, hormone, degree, material, vasoconstrictor, diversion, journey, body substance, change, catecholamine, science, drive, motion, secretion, action, medical science