## 4 Discussion  
The aim of the present study was to characterize the pressures applied during DFM and to determine if a dose-response relationship existed between the pressure applied during DFM and the time to the onset of analgesia in an asymptomatic patellar tendon. Our results indicated that the mean pressure used by the physiotherapists during DFM was 2.3 kg/cm\({}^{2}\) (P25: 1.02 kg/cm\({}^{2}\); P75: 4.16 kg/cm\({}^{2}\)) and the higher the pressure of DFM the shorter the time to the onset of analgesia. Nonetheless, the difference between the lowest and the highest pressures on the time to reach analgesia was 30 s.  
To our best knowledge, this study is the first to quantify and analyze the intensity of the manual pressures applied by physiotherapists during the DFM application. The literature regarding DFM only described the pressures in a qualitative and subjective way as sufficient and constant [11; 12]; this is reflected in the results of study 1, which showed a wide variation on the pressures performed by the physiotherapists. Previous studies have shown that the intensity of the applied pressure has a directly proportional increase in the response of the recruitment and activation of fibroblasts [22; 23]. The pressures described by those authors ranged between 5.1 and 15.3 kg/cm\({}^{2}\), which were much higher than those observed in our study. However, these studies only refer to morphological and histological effects, and the technique was applied longitudinally to the tendinous fibers with an instrument, i.e., the technique was not manual. Furthermore, it should be taken into account that these studies were carried out in animal models [22; 23]. Regarding the influence of the application of different pressures on the time to the onset of analgesia (study 2), our results showed that a higher pressure of DFM led to a decrease in the time to the onset of analgesia, which may reflect a faster response of the presynaptic modulation mechanisms. Thus, a higher intensity of the mechanical stimulus (DFM pressure) will lead to the higher and faster activation of low-threshold A-\(\alpha\) and A-\(\beta\) fibers that inhibit the nociceptive input from A-\(\delta\) and C afferent fibers, which are responsible for nociceptive conduction at the dorsal horn of the spinal cord [4; 5; 10; 13; 14; 15; 28; 29]. The pressure performed during the DFM execution may act as a noxious stimulus, often called counteriritant, which is used as a conditioning stimulus to induce a reduction in the perception of conditioned pain modulation [19; 30]. This mechanism induces analgesia through descending pain modulatory systems, wherein neurotransmitters like serotonin and endogenous opioids have been shown to modulate nociceptive circuits and pain outputs by acting on structures such as the rostral ventromedial medulla and periaqueductal grey (PAG). PAG is a crucial center for the endogenous analgesic system, where the autonomic and somatic responses to a nociceptive stimulus are integrated; moreover, it coordinates the descending activity of noradrenergic and serotonin systems that suppress the nociception between the dorsal horn and the spinal cord [4; 5; 10; 11; 16; 18; 19; 31]. Notwithstanding, the present study used a sample of asymptomatic individuals, and it has been suggested that in conditions of \"no pain\" the descending noradrenergic system that originates in _Locus Coeruleus_ has little influence, playing a minor role in basal pain sensitivity [17; 32]. However, the reader should take into account the fact that the highest pressure only reduced the time to the onset of analgesia by 30 s (comparison between the lowest and the highest pressures), which raises the question about the clinical relevance of such a difference. Some limitations should be acknowledged. First, it is important to point out that both studies were performed in asymptomatic individuals, which may interfere not only with the pressures applied by the physiotherapists (study 1) but also interfere with the pain modulation mechanisms (study 2).