Muscle injuries are frequent traumatic events in daily life, particularly during sports. In sports, their incidence varies from 10% to 55% of total injuries. According to the Mueller Wohlfart classification, muscle injuries are classified into direct traumatic injuries (contusion-laceration) and indirect traumatic injuries, which are further divided into non-structural injuries (grade I and II) and structural injuries. Structural lesions are further divided into partial muscle lesions (grade III): 3 A, minor partial lesion, i.e. lesion of one or more primary bundles with a secondary bundle; 3 B, moderate partial lesion, i.e. lesion of at least one secondary bundle and with a rupture area < 50% of the muscle surface; and (sub)total muscle injury (grade IV).

In the acute phase, the current management of muscle injuries is essentially based on the PRICE protocol (protection, rest, ice, compression, elevation), although there are still no randomized clinical trials in the literature demonstrating its real effectiveness. Subsequently, the player undertakes rehabilitation with exercises and therapies aimed at resolving the edema, repairing the injury, strengthening the muscles and restoring athletic movements.

Biostimulations (laser therapy, diathermy, US, etc) are applied in muscle lesions for their analgesic and anti-inflammatory action, but to date there is a lack of adequate clinical evidence. The high energy laser has a great penetration force deep into the tissues and through its photochemical effects, increases mitochondrial oxidation and facilitates the formation of adenosine triphosphate (ATP), as well as inducing an increase in metabolism and blood circulation, with rapid absorption of edema and elimination of exudates. This induces an important biological action, causing muscle relaxation and inhibition of free nerve endings resulting in an immediate reduction in pain.

Preclinical studies have shown that physical therapies, such as high-energy laser therapy, improve muscle regeneration. On the other hand, to date few clinical studies have investigated the effects of biostimulations on muscle injuries. Medeiros et al. did not find benefits in the application of low energy laser in the treatment of muscle injuries, hypothesizing that a late application may have undermined the effects of biostimulation, which is fundamental in the first days of a late injury. Scaturro et al. , applying a combination of high energy laser and diathermy in association with rehabilitation treatment within 5 days of muscle injury, found positive effects on pain remission, return to sporting activity and the number of relapses. On the other hand, in this study, the contextual administration of two biostimulations (high energy laser and tecar therapy) does not allow us to discriminate the biological and clinical effects attributable to each of the two therapeutic methods.

Therefore, the aim of the present study is to investigate the effects of high intensity laser therapy in the treatment of lower limb muscle injuries.

Inclusion Criteria:

• presence of a grade III A muscle lesion of the lower limbs, according to the Mueller-Wohlfart classification, confirmed by ultrasound examination and occurred during sporting activity at least 5 days before inclusion in the study;
• no previous muscle injury in the last 6 months;
• signing of the written informed consent for participation in the study.

Exclusion Criteria:

• previous muscle injuries or bone fractures of the lower limbs in the last 6 months;

• knee instability due to previous rupture of the knee ligaments;

  • instability or previous sprain of the ankle;

• active neoplastic or infectious diseases;

• contraindications to biostimulation;

• congenital anomalies of the lower limbs.