Giant Fibres

In pork and beef

 A type of muscle degeneration may occur in live PSS pigs (i.e., pigs with porcine stress syndrome, associated with the ryanodine gene, which can be recognised by their sensitivity to the anaesthetic gas, halothane). Pigs that survive bouts of severe stress suffer considerable damage to their muscles, either as a consequence of severe contraction or from anoxia. Muscle fibers may be found with greatly enlarged diameters along part of their length. Similar giant fibers may be found in PSE pork  (i.e., in meat after slaughter), but also they occur in bovine muscle and in turkey breast muscles ,where they are associated with toughness.

Experimentally induced stress lesions in PSS pigs are characterized by swelling of the muscle fibers, loss of transverse striations, and accumulation of proteinaceous materials between the muscle fibers. Giant fibers may be devoid of transverse striations, mitochondria and sarcoplasmic reticulum, and may have increased numbers of dark- staining nuclei.

Since muscle fiber degeneration and giant fibers also may be found in non-PSS pigs, degenerative changes in PSS and PSE may represent severe cases of regular muscle damage resulting from transport and slaughter stress. Stretch-induced injury of muscle fibers caused during tetanic contraction damages sarcomere structure in some parts of the fiber and not others, even though activation of the fiber is uniform .

On the other hand, some researchers argue that giant fibers in pork are not degenerative and that they are similar in nature to the hypertrophied fibers seen in functionally overloaded muscle. Supercontracted fibers occur in both normal and PSS pigs but are more common in the latter.

Focal myopathy

Another condition that may or may not be relevant to the phenomenon of giant fibers in meat animals is FOCAL MYOPATHY in turkeys. Most researchers have concluded that the appearance of giant fibers in turkeys indicates the existence of a myopathy (look for papers by Sosnicki  and  Wilson). In some situations giant fibers appear alone at the edge of a fasciculus, like those found in pigs. However, they also may appear in clusters surrounded by degenerating fibers with a small cross-sectional area and an irregular shape. The incidence of focal myopathy in turkeys is correlated with the rapidity of muscle growth and there is some concern that this condition is a consequence of intensive selection for growth rate.

So, you have some giant fibres in your sample, and you want to know what sort you have?

From the above, it follows that we have three main possibilities:

(1) giant fibres caused by radial hypertrophy - IN WHICH CASE SARCOMERE LENGTH WILL BE UNIFORM ALL ALONG THE FIBRE, AND BOTH ENDS OF THE FIBRE ARE PROPERLY INSERTED EITHER TO TENDON OR THE INTRAMUSCULAR CONNECTIVE TISSUES .

(2) Giant fibres caused by postmortem artefacts:

(i) local contracture nodes caused by removing pre-rigor muscle - IN WHICH CASE SARCOMERE LENGTH WILL BE VERY SHORT IN THE NODE, WHILE ADJACENT REGIONS OF THE FIBRE ARE STRETCHED WITH LONG SARCOMERES {this is a common occurrence in the removal of  biopsy samples from live muscle}, or

(ii) detachment of fibres from their insertions at one or both ends - IN WHICH CASE SARCOMERE LENGTH IS UNIFORM ALONG THE FIBRE, USUALY SHORT SARCOMERES BUT MAY BE REST LENGTH,  HOWEVER,  ONE OR BOTH ENDS OF THE FIBRE ARE FREE .

(3) Giant fibres caused by mechanisms 2i or 2ii, but before slaughter in the live animal - IN WHICH CASE, THEIR APPEARANCE DEPENDS ON THE TIME DELAY BETWEEN THE TRAUMA AND THE SAMPLING. WITH A SHORT DELAY THEY APPEAR THE SAME AS 2i OR 2ii, BUT WITH A LONG DELAY, CLASSICAL SIGNS OF FIBRE DEGENERATION SET IN {hyaline apeearance, pycnotic nuclei, etc).

In other words dear researcher, to know what you really have in your samples, you must cut longitudinal sections!  Which you probably did not do, so you will never know.  Next time, eh?