Answer
$(a)$ increased muscular activity.
$(b)$ lactate produced by anaerobic glycolysis is converted to glucose and
glycogen which requires ATP and therefore $O_{2}$.
Work Step by Step
$(a)$ increased muscular activity increases the demand for ATP, which is met by increased $O_{2}$ consumption.
$(b)$ After the sprint, lactate produced by anaerobic glycolysis is converted to glucose and glycogen, which requires ATP and therefore $O_{2}$.
