MUSCLE PERFORMANCE: TYPES OF MUSCLE FIBRE – SLOW FIBRES & INTERMEDIATE FIBRES
Slow fibres
are only half the diameter of fast ones and take almost three times as long to contract after stimulation, but they can remain contracted for a longer period of time. These muscle fibres have myoglobin, a dense network of capillaries, many mitochondria and have smaller glycogen reserves (that is why they are not bulky muscles). These muscle fibres use other sources of energy as well, such as carbohydrates (amino acids, fatty acids). The muscles have less power but more endurance and, as they use aerobic utilisation of glucose to generate the moderate demand for energy molecules, they do not fatigue so easily. The rich blood supply ensures that the oxygen demand is met and the waste products are removed adequately to maintain the contractions of these muscle fibres. Slow fibres are responsible for posture (sitting, standing) and can remain contracted for a long period of time without getting fatigued. As these muscle fibres have myoglobin and a rich network of blood capillaries, they are dark red in colour (true red meat).
Intermediate fibres
have properties intermediate between those of fast and slow muscle fibres. They have more endurance than fast muscle fibres and more power that slow muscle fibres. Marathon runners train to develop this type of muscle as they have power as well as endurance.
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