## 4 Discussion  
The present study aimed to compare the effects of the DN technique and the DF technique on the stiffness and tone of the teres major muscle, pain intensity, shoulder ROM, and posterior muscle shoulder extensibility. The results of our study showed that a single session of an invasive instrumental technique or a conservative instrumental technique in the teres major muscle decreased teres major muscle stiffness and improved pain intensity, shoulder ROM, and extensibility immediately after the intervention and at one-week of follow-up without statistically significant differences between both groups. Concerning the mechanical properties, muscle stiffness is defined as the ratio of the change in resistance to the change in length [36], and muscle tone is characterized by the muscle stiffness together with elastic properties and neurogenic factors and is responsible for ensuring efficient muscle contraction, such as in steady-state conditions without voluntary contraction [37]. Previous studies have investigated the effects of DN and DF on the mechanical properties of different muscles. [PERSON] et al. [22] found a decrease in upper trapezius muscle stiffness at 72 h of follow-up with a moderate effect size after a single session of DN, but no changes were found in tone. [PERSON] et al. [21] found a decrease in gastrocnemius muscle stiffness and tone at 30 m of follow-up after a session of DF. This is the first study to compare the effects of both techniques on the mechanical properties of the teres major muscle after an intervention and at one-week of follow-up. No statistically significant differences were found in teres major muscle stiffness and tone after a single session of DN or DF. Regarding the within-groups change scores, the results of both groups did not reach the MDCs. No statistically significant between-group differences were found in pain intensity, shoulder ROM, or muscle extensibility. Previous studies have shown that both techniques are effective for decreasing pain and increasing shoulder ROM and extensibility. [PERSON] et al. [7] found an improvement in pain intensity, shoulder ROM, and extensibility in elite handball athletes after a single session of ultrasound-guided DN in the teres major muscle. [PERSON] et al. [13] found an improvement in shoulder ROM after a single session of DN in patients with a painful shoulder. The results of our study found that neither technique was superior to the other in patients with shoulder pain and GIRD. The within-group analysis showed that the change scores of both groups at both timepoints achieved higher values than the SEMs and MDCs described for all the secondary outcomes except for extensibility in the DN group. From a clinical point of view, a higher muscle stiffness and/or a lack of muscle extensibility have shown to be linked with a restricted ROM [38]. Multiple interventions have been applied to the posterior shoulder muscles in order to decrease its stiffness or improve its extensibility such as manual therapy [39], muscle stretching [40], muscle energy techniques [41], taping and kinesiotaping [42; 43], or DN [44]. All of them found improvements in pain intensity and/or shoulder ROM, exposing a relationship between the posterior shoulder muscles and shoulder ROM. In this case, we compared an invasive intervention to a conservative intervention to change the mechanical properties of the teres major muscle, pain intensity, shoulder ROM, and muscle extensibility but neither achieved better results than the other, so no recommendation can be made. This study presents some limitations. First, only one treatment session was applied, and the outcome measures were registered over a short-term follow-up period (one week). So, no medium- or long-term outcomes were assessed. Secondly, only male elite handball athletes were included in the study and therefore cannot represent all overhead athletes, so these results cannot be extrapolated to other genders or populations.