Muscle fibers, the inside story Until the early 70s, it was difficult to study exactly what happens inside muscles during exercise, but the technique of muscle biopsy has changed ail that. With muscle biopsy we can safely gain valuable information about an individual's physiological make-up. The subject is given a local anesthetic, and then a half-inch incision is made into the muscle and the needle inserted. Since muscle has no pain receptors, the insertion doesn't hurt. A sample of 20-40 milligrams of muscle tissue is extracted, enough for several biochemical tests, including fiber typing.
All muscle fibers contract to their greatest possible tension when stimulated.
However, fibers differ in their rate of contraction. Certain muscle fibers can contract repeatedly without much fatigue. It has a high aerobic capacity, which means it can produce energy at a steady rate for a long time when enough oxygen is available. Red fiber develops peak tension slowly, about 0.1 seconds after stimulation. The other major fiber type has less myoglobin, which makes it look whiter.