## 4 Discussion
As occurred with Cr, CK is a cytoplasmic enzyme abundant in skeletal muscle, so it was to be hoped that resting levels and post-exercise circulating CK concentrations were higher in males than in female players. Although, in general, padel could be classified as low-moderate impact sport, successive shots and explosive actions during rallies seem to induce disruptions in muscle fibers and the release of CK to the bloodstream. In fact, exercise-induced muscle damage and, consequently, increases in blood CK levels are related to highly repeated muscle contractions [30]. Another typically muscle damage biomarker used in sports science research is LDH. As CK and other intracellular molecules and enzymes, the appearance of increased levels of this biomarker in the blood indicates to changes in muscle fiber membrane permeability as well as cellular disruption, damage, and death, which has been observed in response to exercise [31]. Supporting the results reported by [PERSON] et al. [9], our findings showed increases in blood LDH concentrations when total group was considering. Accordingly with these previous data, sex-related differences were also found in both pre- and post-padel matches assessments since LDH levels were higher in male than in female players. However, pre- to post-exercise analysis performed in our study revealed significant increases in females but not in males which was not observed in previously published data [9]. A novelty of this study was using FABP-3 as muscle damage biomarker. Although FABP-3 was initially investigated as a marker of cardiac injury in experimental animal models, this fatty-acid binding protein has been proposed as a muscle damage biomarker due to its presence in skeletal muscle. In fact, it has been reported that circulating FABP-3 levels increase and decrease more rapidly than CK, indicating that FABP-3 is more useful than CK for the early detection of skeletal muscle injuries and the monitoring of injury during repeated exercise bouts [32]. Considering the total group, two-fold significant increases in blood FABP-3 levels were observed. Moreover, similar responses were also reported in both male and female groups after padel matches, although no statistical sex-related differences were found. While previous studies reported higher serum FABP-3 levels in males than in females, and the gender difference was attributed to larger muscle mass in males [33], our results seem to be in accordance with those reported by [PERSON] et al. [34], who did not find sex differences in FABP-3 resting levels. Our results have practical implications for both improving padel performance (they could help to coaches to gain a better understanding of metabolic demands of padel match play and to design better training programs) and avoiding adverse effects of training overloads which could lead to impaired recovery of damaged muscles, increasing the susceptibility to injury. This last point is important given the popularity and social characteristics of padel, with many inexperienced or beginners players joining padel clubs and participating in a number of amateur leagues and tournaments. In fact, the increases in circulating muscle damage biomarkers observed (LDH, CK, FABP-3) inform about the impact of padel match play in trained players; however, how would it affect players whose padel movements and strokes are not well-skilled? Future studies should be focused on the use of these biomarkers for monitoring the impact of padel on the musculoskeletal system of this population. Finally, as with most one group pre-post study designs in sports science research, the present findings should be interpreted with caution due to several limitations. Firstly, we use a convenience sampling of trained padel players who regularly participate in padel competition events. Although the sample size was calculated to achieve adequate study power, morphological and performance characteristics of players could compromise external validity of the results.