MUSCLE PERFORMANCE: TYPES OF MUSCLE FIBRE - FAST FIBRES
Muscle performance is characterised by power, the maximum tension an individual muscle or a group of muscles can produce, and endurance, the amount of timefor which an individual can perform that activity. Two major factors determine muscle performance: the types of muscle fibres involved and physical conditioning and training.
Types of muscle fibre
There are three major types of skeletal muscle fibres, known to myologists, in the human body: fast (twitching), slow (twitching) and intermediate (twitching) fibres.
Fast fibres
constitute the vast majority of skeletal muscle and they acquire their name from the fact that they can twitch, or contract-and-relax, very soon after stimulation (in approximately a 100th of a second). They are large in diameter, contain densely packed myofibrids, have large glycogen (stored glucose) reserves and relatively less myoglobin and fewer mitochondria. They are geared up for immediate and quick action. They do not have the time to wait for slow blood flow and therefore have very few capillaries. These muscles produce powerful and quick contractions and therefore have no time or capability for utilising oxygen to produce energy molecules (thus less blood flow, fewer mitochondria, less myoglobin). They use the quick and convenient anaerobic path of glucose utilisation, thus producing more lactic acid as a by-product. This is why fast muscle fibres fatigue so easily. They do their job and fag out. A sprinter dashes for the 100m race and almost collapses at the end as he or she is barely able to stand for a few minutes. Ask them to run another race shortly afterwards and the result will be very poor performance. Poorly trained runners get 'a stitch' -a spasm with pain. These muscles have no endurance to match other types of muscle fibres. As they have poor blood supply and less myoglobin, they are pale in colour.
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