For example, a friend of yours goes to the gym and takes a 30-minute, cardio interval training class. While switching between doing high-intensity push-ups, jumping jacks, and weight training, she notices that there is a burning sensation in her muscles. The burning is due to the buildup of: a. creatine phosphate
b. lactate
c. alcohol

in the muscle tissue, a result of her muscles supplying ATP:

a. anaerobically
b. aerobically

b. lactate

a. anaerobically

Explanation:

In the body, energy is produced aerobically in the presence of oxygen, however, during tough exercises, breathing begins to occur faster in an attempt to produce more oxygen to make energy for the muscles to continue to work. But in the case of strenuous exercise,  the body evades the need for oxygen to produce energy, therefore, energy is now produced faster, anaerobically for the working muscles. This energy produced is through the breakdown of glucose, in a process called glycolysis. Glucose undergoes a ten-step reaction where it finally broken-down to pyruvate. Normally, in aerobic conditions, pyruvate is further metabolized to produce energy, but in anaerobic conditions, such as in strenuous exercise, pyruvate is temporarily converted to lactate to produce energy for the working muscles.

During strenuous exercises, lactate rapidly builds up in the muscles and this can result to rapid breathing, soreness and burning sensation in the muscles.