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
pull oxygen through the skin in order to continue working.
b
start anaerobic respiration, producing lactic acid buildup.
c
stop functioning properly, resulting in cramps.
d
send signals to the brain telling it to shut the muscles down.
b
start anaerobic respiration, producing lactic acid buildup.