## 4 Discussion
In agreement with these latter results of this systematic review were two other systematic reviews [21; 49], which found a statistically important improvement in QoL after PFM exercises with BF. [PERSON] et al. [21] also showed that the combination of BF with PFM exercises in comparison to alternative interventions (PFM exercises alone, electrostimulation and no training) were not better. On the other hand, UK International Guidelines [50] support that the combination of PFM with BF has had better results concerning QoL (than PFM exercises alone). The results concerning satisfaction to treatment could not be supported because of the lack of studies (only two moderate-quality studies) examining this outcome. However, in one study [30], patients in both groups were satisfied with the treatment and did not desire to participate in a different group. In the study of [PERSON] et al. [28], women in the BF groups were more satisfied than women in the non-BF group. Finally, adherence to treatment was found better in the BF group in two studies [26; 32], better in the non-BF group in one [25] and similar between groups in three studies [24; 30; 31]. In [PERSON] et al. 's [36] study, it was observed that the frequency of exercise followed at home decreased during the nonsupervised exercise period. This came to an agreement with two other studies [51; 52], emphasizing the role of supervision in adherence to exercise programs. In [PERSON] et al. 's [34] high-quality study, the EMG group showed greater adherence compared to the vaginal probe and non-BF groups. Women in the vaginal probe BF group reported adverse effects (burning and painful urination, discomfort, skin damage near the vaginal region), resulting in the discontinuation of the intervention. Additionally, in the Cochrane review [40], it was supported that adverse events were associated with intravaginal probes leading to the discontinuation of the intervention. This fact may have affected the results. Others supported that the EMG-BF had an advantage over manometric pressure biofeedback due to the fact that it can accommodate new types of electrodes that are lightweight, more sensitive and designed to stay in place, thus, allowing for a more functional body position for assessment and treatment [43]. In one moderate-quality RCT [28], two BF groups (perineal EMG-BF and intravaginal pressure BF) were included. The results concerning muscle strength, QoL, social life and the severity of incontinence were similar between the groups at both 4 and 8 weeks. It should be noted that the level of discomfort was significantly higher in the intravaginal pressure BF group compared to the EMG-BF group at the 4-week reassessment. In contrast, in [PERSON] et al. 's high-quality study [34], the EMG-BF group was superior to the vaginal probe BF group concerning muscle strength and the severity of incontinence. However, these results must be interpreted with caution due to the underpowered pilot trial. The findings of this systematic review add novel contributions to the existing literature. As it has been known, the first-line treatment for urinary incontinence is PFM exercises [8]. Most RCTs included in this review showed that PFM exercises with BF had a significant effect in muscle strength and the severity of incontinence compared to PFM exercises without BF. It is also important to note that besides the significant effect of the combination of PFM exercises with BF on muscle strength and the severity of incontinence, a significantly improvement was also shown in other muscle parameters (such as endurance, precontraction and function), QoL and social life compared to the baseline. As a result, PFM exercises with BF had an important therapeutic effect in women with urinary incontinence. However, it should be noted that these results were based on RCTs that showed heterogeny concerning the type of PFM exercise and the follow-up period.