## 4 Discussion  
The present study compared the short-term outcomes of two rehabilitation treatment regimens (the Multiwave Locked System laser therapy versus the combined TENS and ultrasound therapy) in the treatment of the subacromial pain syndrome. Both treatment regimens showed an improvement in analyzed outcomes (pain, functionality and disability). In addition, MLS therapy with physical therapy exercises may have clinical advantages over the combination of TENS, US and exercises in the treatment of SAPS, with a significant improvement in pain and functional disability. SAPS is a common cause of shoulder pain and disability. Management of SAPS includes several non-surgical and surgical treatment procedures. The conservative procedures' objectives are to reduce pain, inflammation, to improve range of motion and to stimulate the tendon's healing [7]. Studies have investigated different treatment strategies, with exercises being the most important component [23; 24]. To our knowledge, there are no studies investigating the effects of MLS in the treatment of SAPS. [PERSON] et al. [25] reported an improvement of pain and function in patients with different trantionopathies treated with MLS. Their patients with shoulder trantionopathies had positive, but statistically non-significant results, due to the small sample size. Our results showed a significant decrease in pain as assessed by VAS and also a significant improvement in functionality, as assessed by SPADI. The improvement in SPADI scores was significantly greater in patients treated with MLS laser therapy. In our study, the improvements seen in pain, functionality and disability after both treatment regimens have been proved to be not only statistically significant, but also clinically relevant, the changes in scores being greater than the reported MCIDs. Since the 95% confidence interval for the differences at follow-up and for the changes overlaps the MCID for VAS and SPADI, the observed differences could be possibly clinically significant, but no conclusion could be drawn until more data are obtained [26; 27; 28]. The effects of high-intensity laser therapy in subacromial impingement syndrome have been studied by [PERSON] et al. [29]. The author reported the short-term effectiveness of high-intensity laser therapy, decreasing pain and improving disability. The change seen in SPADI score in the above-mentioned study is in accordance with our results, with a decrease in pain and disability. [PERSON] et al. compared the short-term effects of high-intensity laser therapy versus ultrasound in subacromial impingement syndrome patients and found a greater reduction in pain and improvement in articular movement functionality in the affected shoulder in patients treated with high-intensity laser [30]. The analgesic and anti-inflammatory effectiveness of MLS therapy has been observed in different pathologies like chronic neck pain, knee osteoarthritis, Raynaud phenomenon, bursitis, carpal tunnel syndrome, and myofascal pain [13; 31; 32; 33; 34; 35; 36]. In their study, [PERSON] et al. [37] observed an anti-inflammatory effect and also an improved collagen fiber organization in an experimentally induced trantionopathy in sheep after the use of MLS in doses of \(2.5\,\mathrm{J/cm^{2}}\). Moreover, a study conducted in Poland on 30 patients with rheumatoid arthritis showed the effectiveness of MLS laser therapy in reduction of pain and swelling of joints but also an improvement of hand function and quality of life [38]. The analgesic and anti-inflammatory effects of MLS could be explained by the photothermal and photochemical effects induced in the deep tissues, increasing the collagen production and improving blood flow, cell metabolism and vascular permeability [39]. The therapeutic effects of US are mainly due to its thermal properties, improving circulation and elasticity of collagenous tissues, decreasing muscle spasms and destroying scar tissue [40]. Our study has some limitations, and the relatively small number of patients in both groups is one of these limitations.