On a backpacking trip, Kenny hikes all day at a steady pace, covering 30 kilometers and burning 4000 Calories. At the school track, Janelle runs the 100-meter sprint in 13.5 seconds, burning 10 Calories. Afterward, Janelle’s leg muscles are aching and she is breathing hard, while Kenny maintains normal breathing all day, even though he burns 400 times more calories than Janelle. Which two statements offer the BEST explanation for this phenomenon?