If this is fresh muscle, micro dissection should be possible.  Rat gastroc has more connective tissue than most so look around and you'll probably find areas that are easier to dissect.  It it usually consistent across muscles.  

See our publication doing this in human muscle biopsies:  Fridén, J. and R.L. Lieber.  (2003).  Spastic muscle cells are shorter and stiffer than normal cells.  Muscle & Nerve 27:157-164. PMID12548522

Also, many doing this in fixed tissue (probably not applicable).  See, for example:    Eng, C.M., L.H. Smallwood, M.P. Rainiero, M. Lahey, S.R. Ward and R.L. Lieber (2008). Scaling of muscle architecture and fiber types in the rat hindlimb.  J. Exp. Biol. 211:2336-2345. PMID18587128

Thank you! 

My experience of trying to dissect out single fibres is not so encouraging!  Another approach is to use collagenase to try and separate out the fibres and this approach has been used by Malcolm Jackson's group to various things that are similar to your interest.

Studies of mitochondrial and nonmitochondrial sources implicate nicotinamide adenine dinucleotide phosphate oxidase(s) in the increased skeletal muscle superoxide generation that occurs during contractile activity.

Sakellariou GK, Vasilaki A, Palomero J, Kayani A, Zibrik L, McArdle A, Jackson MJ.

Antioxid Redox Signal. 2013 Feb 20;18(6):603-21. doi: 10.1089/ars.2012.4623. Epub 2012 Dec 6.

PMID:

23050834

Free PMC Article