What stimulates increased respiration at the beginning of exercise?
a. decreased plasma oxygen levels
b. increased hydrogen ion levels
c. increased plasma carbon dioxide levels
d. sensory input from receptors in joints, neural input from the motor cortex, and other factors

d. sensory input from receptors in joints, neural input from the motor cortex, and other factors is the correct answer

Explanation:

sensory input from receptors in joints, neural input from the motor cortex, and other factors stimulates increased respiration at the beginning of exercise.  As we do exercise our muscles gets active, it produces lactic acid that enters the blood and hydrogen ions are a release that reduces the pH due to a decrease in the pH stimulates the sensory receptors to carry nerve impulses to respiratory muscles and this increase respiration at the beginning of the exercise.In medual the respiratory center is stimulated by increasing the carbon dioxide concentration.