Radha was running on a treadmill at a great speed for 15 minutes continuously. She stopped the treadmill and abruptly came out. For the next few minutes, she was breathing heavily/fast. Answer the following questions.
(a) What happened to her muscles when she did strenuouly exercised?
(b) How did her breathing rate change?

Explanation

(a) Due to strenuous exercise on a treadmill, the oxygen demand of the body tissues increased much more. To meet oxygen demend, glycogen was anaerobically catabolised which produced `CO_2` and lactic acid. Accumulation of lactic acid caused muscle fatigue.
(b) Increase in `CO_2` level in the biood and lactic acid in muscles both initiate excitatory signals and increase the rate of breathing.