When an individual exercises vigorously for more than 15 minutes, the muscle cells are unable to obtain oxygen from the blood quickly enough. As a result, the muscle cells
a
send signals to the brain telling it to shut the muscles down.
b
start anaerobic respiration, producing lactic acid buildup.
c
stop functioning properly, resulting in cramps.
d
pull oxygen through the skin in order to continue working
b
start anaerobic respiration, producing lactic acid buildup.
b
start anaerobic respiration, producing lactic acid buildup.
The correct answer is b. When an individual exercises vigorously for more than 15 minutes, the muscle cells are unable to obtain oxygen from the blood quickly enough. As a result, the muscle cells start anaerobic respiration, producing lactic acid buildup.
To understand why this happens, we need to know how energy is produced in our muscles during exercise. Normally, during aerobic respiration, our muscles are able to break down glucose (sugar) with oxygen to produce energy in the form of adenosine triphosphate (ATP). This process is efficient and sustainable for longer periods of time.
However, during intense exercise, the demand for oxygen by the muscles exceeds the supply. This is known as oxygen debt. When the oxygen supply is limited, the muscle cells switch to anaerobic respiration, also known as glycolysis. In this process, glucose is broken down without oxygen, producing ATP but also lactic acid as a byproduct.
Lactic acid buildup in the muscle cells lowers the pH level, which can lead to muscle fatigue and discomfort. The accumulation of lactic acid is associated with the burning sensation and fatigue experienced during intense exercise. The increased levels of lactic acid can eventually lead to muscle cramps if the exercise continues.
So, when an individual exercises vigorously for more than 15 minutes and oxygen supply is limited, the muscle cells start anaerobic respiration, producing lactic acid buildup.