What type of respiration takes place in human muscles during vigorous physical exercise? Give reason for your answer.

(N/A) $1$. During vigorous physical exercise, the demand for energy in muscle cells increases significantly.
$2$. The supply of oxygen by the blood cannot keep up with this high demand.
$3$. Consequently, the muscle cells switch to anaerobic respiration to produce energy.
$4$. This process leads to the production of lactic acid, which causes muscle fatigue.