## 4 Discussion
### Low-Load Blood Flow Restriction Training and Muscle Strength  
Considering the results reported by each of the selected studies individually, it can be stated that the knee extensor muscle strength improved after the LLBERT intervention. Significant intragroup differences in quadriceps strength supporting the LLBERT group were observed between four and twelve weeks post-intervention in five studies [33; 39; 41; 42; 43]. Similarly, positive effects were reported for knee flexor strength, with improvements in hamstring peak torque (\(p<0.05\)) at eight weeks [33] or twelve weeks [39] after LLBERT intervention. Moreover, other studies have also highlighted findings such as a 78% or 39% increase in both knee extensor and knee flexor isokinetic strength [45]. On the whole, it is observed that the greatest muscle strength enhancement occurred in the LLBERT groups at 80% AOP, in some cases even finding significant intragroup differences with the 40% AOP group [41; 42].  
These results support the hypothesis that LLBERT has greater positive effects on muscle strength than conventional resistance training in the initial postsurgical phase. This is mainly sustained by the published literature on LLBERT and knee surgery, particularly after ACL reconstruction. [PERSON] et al. [53] and [PERSON] et al. [54] stated the beneficial effects of LLBERT, preserving or even increasing quadriceps strength. More specifically, [PERSON] et al. [55] and [PERSON] et al. [56] confirmed this improvement in their trials, which resulted in significant increases quantified between 20 \(\pm\) 14% and 84 \(\pm\) 47% in the post-intervention knee extension strength. Conversely, some studies also support our findings regarding hamstring strength. For example, [PERSON] et al. [30] reported a positive variation in the knee flexor peak concentric torque at 60\({}^{\circ}\) and 180\({}^{\circ}\) (\(p<0.05\)) after the intervention. [PERSON] et al. [56] noted an improvement in mean peak knee flexor strength (\(p<0.01\)) after nine LLBERT sessions. However, other studies have questioned these results. A recent publication stated that there is no solid evidence of the positive effects of LLBERT on knee extensor muscle endurance [57]. Although differences in intervention protocols and variability in post-surgical patients' conditions could affect the results, the findings of our meta-analysis support this statement. In fact, the overall effect for the selected studies (i.e., cases) was opposite to the predictions. This contrary effect was more remarkable in the studies performed by [PERSON] [41] (SMD between 2.41 and 2.74; \(p<0.001\)) and [PERSON] [42] (SMD = 1.49; \(p<0.001\)), in which low-load resistance training (without blood flow restriction) was used as a control strategy.  
Nevertheless, few studies have assessed the effects of LLBERT on upper limb muscle strength after surgical intervention. Previous studies reported increases in external and internal shoulder rotation as well as shoulder abduction strength after twelve weeks of LLBERT intervention (\(p<0.01\)) [58]. Similar results were found by [PERSON] et al. [59], who evaluated the effects of a 10-wk LLBERT program on upper limb strength in a postsurgical biceps brachial patient.  
Two of our selected articles focused on the effects of LLBERT on operated upper limb muscles. The cases extracted from the study by [PERSON] et al. [46] showed remarkable effects in favor of the control intervention (SMD between 2.48 and 2.95; \(p<0.001\)), especially when pinch strength and wrist extension and flexion were tested. For their part, [PERSON] et al. [47], whose study could not be finally included in our meta-analysis, did not find significant differences between the intervention and control groups after an 8-wk LLBERT program focused on grip and pinch strength.  
Thus, considering the above, it is not possible to provide meta-analytic evidence of the differential benefits of LLBERT as a therapy strategy focused on the strength of the operated muscles.