## 4 Discussion  
The present study analyzed the effects of an isolated NMES intervention on the quadriceps muscle and its combination with BFR on parameters related to muscle performance in amateur female football players. Rehabilitation strategies for the prevention of muscle injuries in football include programs based on increasing strength as the gold standard [40].  
Regarding muscle strength, there was an increasing trend in both MVEC and MVCC in the NMES group and a decreasing trend in the NMES + BFR group for both variables, although these differences were not statistically significant either within or between groups. A loss of muscle strength after intense physical exercise can affect performance, reduce the quality of training, and increase the risk of injury [41]. Our findings differ from previous studies that found improvements in quadriceps muscle strength after the simultaneous application of NMES and BFR [8,9]. These differences could be explained by the timing of the measurement. Our results correspond to immediate post-intervention effects. According to previous studies performed with BFR [14,15], at least two weeks are required to induce significant architectural changes and achieve muscular hypertrophy. Likewise, these immediate effects may be influenced by fatigue. The fact that the NMES + BFR group showed strength loss trends (Table 3) could be explained by the combination of a 50% duty cycle with vascular occlusion by BFR. This parameter has been associated with the incipient development of muscle fatigue in healthy subjects [33].  
For fatigue control, the intensity of the stimulation was increased during each exercise included in the procedure in accordance with participant tolerance [42], and the load was 20% of the MVCC [33]. [PERSON] et al. observed differences in fatigue induced in conditions which used different types of current (low frequency vs. medium frequency). In healthy athletes, when the aim is to generate more muscle work with less fatigue during training, the preferred option is NMES using a symmetric biphasic pulse [33], as applied in the present study.  
Regarding muscle volume, thigh circumference showed statistically significant increases in all measurements in both groups, showing a small effect size. All changes were above the SEM. However, no significant changes were observed between groups, which could indicate that the increase was not due to an adverse reaction of muscle damage after the application of BFR [43,44]. [PERSON] et al. [8] observed an increase in muscle thickness after combining NMES and BFR at a low load for 2 weeks, which was lost after the same period without training. According to [PERSON] et al. [15], metabolic fatigue can trigger an increase in acute cellular inflammation. These phenomena can increase the rate of muscle protein synthesis to trigger muscle hypertrophy [8]. [PERSON] et al. [45] highlighted post-exercise muscle inflammation as a factor contributing to hypertrophy. Future studies should analyze the architectural parameters of the muscle to understand immediate changes, their relationship with muscle growth, and how long adaptations can prevail.  
On the other hand, knee repositioning capacity did not show statistically significant differences either within or between groups. [PERSON] et al. [31] observed how the sensory acuity of the knee joint position decreases after the onset of fatigue during exercise in amateur football players. This proprioceptive reduction has been attributed to increased concentrations of metabolites and inflammatory substances in the fatigued muscles [46]. A deficit in proprioceptive acuity or joint stability could affect motor control accuracy and efficiency of movement during a game, increasing the risk of injuries [47]. The absence of immediate changes in this parameter could be beneficial for avoiding proprioceptive impairment in players.