Final answer:
"Hitting the wall" in a marathon is commonly due to the depletion of glycogen, the body's stored form of glucose for energy. A marathon runner's body relies on this glycogen to produce ATP, and when levels run low, performance is significantly hindered. Exercise physiologists study these phenomena to better understand energy use during endurance sports.
Step-by-step explanation:
When a marathon runner experiences the phenomenon known as "hitting the wall," the nutrient that is most likely depleted is glycogen. Marathon runners often practice carbohydrate loading to increase glycogen stores, which serve as an essential energy reserve. During a marathon, the body uses glycogen to produce glucose, which in turn is converted into ATP through the process of cellular respiration, providing the energy needed for muscle work.
As a marathon progresses, stored glycogen levels can become critically low, leading to fatigue and reduced performance. This is often referred to as "hitting the wall." To sustain endurance, marathon runners have a high proportion of slow-twitch muscle fibers (SO fibers), which are more efficient for long-distance running. In contrast, a sprinter would experience muscle fatigue sooner due to the reliance on anaerobic metabolism.
An exercise physiologist is a scientist who would typically study how the body uses foods and fluids during endurance activities like a marathon. Their research helps in understanding the physiological demands of such high-intensity exercises on the body.