The white and red fibres
There are those who like only breasts and those who prefer legs. I’m a leg person, but tastes are known to differ. Why? Breast and leg musculature (I’m talking of the chicken, of course) serve different purposes and, containing different chemicals, also taste differently. Legs, ready for sudden bursts of activity, are “run” by so-called fast, white muscles, which are loaded with glycogen (a carbohydrate) as the main fuel. White muscle fatigues easily, but it has a sweetish taste. Postural muscles like those of the chicken breast and flight muscles in migratory birds on the other hand are designed for long, sustained activities and termed red (or slow) musculature. The do not fatigue easily and contain the reddish myoglobin to supply them with oxygen and nutrients.
Weight-lifters and sprinters tend to use white muscles, but marathon runners rely more on the red muscle type. Unlike smooth muscle, found for example in connection with the intestine and the uterus, the kinds of muscle belonging to the voluntary (i.e., striated, skeletal) muscle category like the already mentioned red and white muscle, are best distinguished by histological staining methods. In fish, however, red and white muscle kinds can be identified by the naked eye without the need to stain them. To test what exercise does to the two muscle types, we looked at their proportions and fibre sizes in Retropinna retropinna, a species of fish known as the New Zealand smelt that has a lake-population (which does not migrate) and a river-population (which does migrate). The river fish swim upstream to reach their feeding and maturing grounds and, unsurprisingly, their red muscle component increases relatively to the white muscle part during the migration.
However, do red muscle cells (usually referred to as fibres) simply grow bigger in size or are they responding to the effort of allowing the fish to swim upstream against the flow of the water by increasing in total number? In our fish the result showed that natural long distance training in the form of upstream swimming was primarily instrumental in causing an increase in the number of red fibres, i.e. muscle cells.
The white muscle, which forms the bulk of the fish’s trunk musculature, behaved quite differently: exercise did not change the overall fibre number, but did cause a significant increase in fibre diameters. Maximum fibre diameter was attained at an earlier age in the lacustrine (= lake) fish and since new white fibres could not be recruited, the phenomenon left the lake fish physically “stunted”, i.e., shorter than the riverine (= river) specimens.
Now, to go back to the beginning, where do I stand when it comes to the question of red and white muscle? I still stand on my two legs, and that I owe to my muscles. Which ones, red or white, you ask? Read the text again.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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