Lesson 7 of 12 · 5 min
Red and white fibres
NCERT §17.2.2
Meher kept up a strong pace for most of the race, but a hard sprint at the end left her thighs burning. Different fibres are built for those two jobs.
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In short
Reaction time varies between muscles.
Repeated activation can build up lactic acid from the anaerobic breakdown of glycogen, which causes fatigue.
Muscle contains myoglobin, a red pigment that stores oxygen. Muscles rich in myoglobin look reddish and are called red fibres.
Red fibres also have plenty of mitochondria that use their stored oxygen to make ATP, so they are called aerobic muscles.
White fibres have very little myoglobin and look pale. They have few mitochondria but a lot of sarcoplasmic reticulum, and depend on anaerobic processes for energy.