## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & \multirow{2}{*}{**Group**} & \multicolumn{2}{c}{**Intervention**} & \multicolumn{2}{c}{**Mean Change**} & \multicolumn{2}{c}{\(p\) (\(\eta^{2}\)) Value**} \\ \cline{3-8}  & & **Before** & **After** & **95\% CI** & **Group** & **Time** & **Interaction** \\ \hline Y-balance anterior & GRE & 48.50 \(\pm\) 8.42 & 51.50 \(\pm\) 5.98 & 3.00 [0.00, 6.00] & 0.454 & 0.000 & 0.046 \\ (cm) & BFR & 44.17 \(\pm\) 6.51 & 51.67 \(\pm\) 7.57 & 7.50 [3.92, 11.08] ** & (0.026) & (0.526) \(\dagger\) & (0.170) \(\dagger\) \\ \hline Y-balance posterior & GRE & 89.92 \(\pm\) 9.88 & 95.92 \(\pm\) 6.19 & 6.00 [13.37, 10.63] * & 0.263 & 0.000 & 0.544 \\ medial (cm) & BFR & 86.08 \(\pm\) 6.54 & 93.58 \(\pm\) 5.48 & 7.50 [4.81, 10.19] ** & (0.056) & (0.583) \(\dagger\) & (0.017) \\ \hline Y-balance posterior & GRE & 89.00 \(\pm\) 7.91 & 91.42 \(\pm\) 7.84 & 2.42 [0.19, 4.64] * & 0.618 & 0.002 & 0.048 \\ lateral (cm) & BFR & 83.75 \(\pm\) 13.25 & 93.17 \(\pm\) 7.38 & 9.42 [2.42, 16.42] * & (0.011) & (0.364) \(\dagger\) & (0.167) \(\dagger\) \\ \hline  & \multicolumn{2}{c}{Values are expressed as to prevent injuries first and to try to eliminate the risk of injury through game analysis. However, this study attempted to provide an effective exercise program for an ACL injury that most frequently appears in knee joint injuries [21, 22, 23]. After surgical treatment due to an ACL injury, the patient can relieve pain through rehabilitation, recover joint function, improve walking and daily living performance and quickly return to daily life [24]. However, immediately after surgery, the muscle strength and activity of the thigh are reduced to half of those before surgery, muscle atrophy occurs by 5 to 20% and joint function deteriorates, accompanied by severe pain due to the incision. Lack of adequate initial rehabilitation treatment can result in low thigh muscle strength and activity and persistent functional impairment, leading to premature disability, falls and a reduced ability to perform activities of daily living [25]. Therefore, restoring lost muscle strength to normal levels is very important. Traditionally, physiotherapy and exercise have been performed for the rehabilitation of patients after surgery, but it is said that successful effects cannot be achieved due to the adjustment of exercise intensity and the patient's anxiety due to pain. In contrast, it is determined that a new rehabilitation exercise method is necessary. Blood flow restriction (BFR) was a method of inducing a hypoxic environment in tissues by restricting blood flow to the muscles by applying pressure to the arms and legs using a device during exercise [19]. Even short-term training at a relatively low intensity (20-30% of 1-RM) can provide similar effects to existing high-intensity training and has been used by various groups such as the public, athletes and patients with illnesses. Therefore, this study investigated the effect of muscle function improvement, muscle hypertrophy and knee functional ability of the quadriceps muscles by performing a 12-week complex exercise using BFR added to the existing rehabilitation process of patients with weakened quadriceps muscles due to ACL reconstruction. [PERSON] et al. [26] conducted an evaluation of the Lysholm score and IKDC subjective score through 8 weeks of BFR and traditional high-intensity resistance training rehabilitation exercises in patients undergoing ACL reconstruction. The BFR-applied group showed a greater effect than the resistance training rehabilitation group. [PERSON] et al. [27] also reported that the Lysholm score and IKDC subjective score showed significant improvement in the BFR group as a result of a study comparing the BFR group and the control group. The results of this study also showed that Lysholm score and IKDC subjective score were improved through rehabilitation exercise, but it was found that the effect of improvement was better in the group that underwent combined BFR treatment.