This study analyzed the effects of light-emitting diode (LED)
therapy on the morphology of muscle tissue as well as
collagen remodeling and
matrix metalloproteinase 2 (MMP-2) activity in the skeletal muscle of rats following acute injury. Wistar rats were divided into four groups: (1) control, (2)
sham, (3) untreated cryoinjury, and (4) cryoinjury treated with LED. Cryoinjury was induced by two applications of a
metal probe cooled in liquid
nitrogen directly onto the belly of the tibialis anterior muscle. For treatment, the LED equipment (wavelength 850 nm, output power 30 mW, and total energy 3.2 J) was used daily. The study periods were 1, 3, and 7 days after cryoinjury. Morphological aspects were evaluated through
hematoxylin-
eosin staining. The amount of
collagen fibers was evaluated using Picro Sirius Red staining under polarized light. The
gelatinase activity of MMP-2 was evaluated using zymography. The results showed significant reductions in inflammatory infiltrate after 3 days and an increased number of immature muscle fibers after 7 days. Furthermore, treatment induced a reduction in the gelatinolytic activity of MMP-2 after 1, 3, and 7 days in comparison to the untreated injury groups and increased the
collagen deposition after 3 and 7 days in the treated groups. LED
therapy at 850 nm induced a significant reduction in
inflammation, decreased MMP-2 activity, and increased the amount of immature muscle and
collagen fibers during the muscle repair process following acute injury.