## 4 Discussion  
This double-blind randomized control trial compared the effect of augmented-reality-based training and conventional therapy on the physical performance of early-stage rehabilitation in patients with TKR. The main finding was that both the ART group and conventional TBT group after 4 weeks of training showed similar results. These findings are  
Figure 5: Comparison of pain and balance within groups. (**A**) Pain, (**B**) balance (anterior–posterior), (**C**) balance (superior–inferior), (**D**) balance (medial–lateral). * \(p\) < 0.05. Figure 6: Comparison of pain and balance between groups. (**A**) Pain, (**B**) balance (anterior–posterior), (**C**) balance (superior–inferior), (**D**) balance (medial–lateral). consistent with previous studies emphasizing the non-superiority of conventional training programs to virtual training programs [22; 23]. One of the purposes of rehabilitation after TKR is to decrease pain and recover knee function, such as ROM, strength, and ability to support weight and balance. In a previous study on the effect of virtual reality on pain and ROM conducted on patients with burn injuries, VR was effective to reduce and manage pain. Nevertheless, they found that VR did not have a significant effect on improving ROM [23]. The authors affirmed that ROM and pain control are different variables, and there is no correlation between the two factors. Some studies reported that training in a virtual or augmented environment provides immersive and multi-sensory effects that allow users to have a sufficient sensation of distraction that allows for reducing pain sensation [24] and improving physical performance [13]. This is the main mechanism that explains the result found in the present study, that training with an AR device reduces pain. This mechanism is known as the \"distraction theory\" or the \"cognitive distraction\" of AR-based training on pain management and physical ability [25]. During AR-based training, patients are deeply engaged in an immersive experience and it becomes difficult to perceive stimulation outside of the field of attention, including pain. For the pain sensation, the thalamus in our brain is one of the most significant structures to receive projections from multiple ascending pain pathways. It also processes pain perception before transmitting various information to the corresponding part of the cerebral cortex. In the human brain, the thalamus handles a variety of pain-related factors, such as emotional motivation (internal pain pathway) and sensory discrimination (lateral pain pathway) components [26]. It is important for pain control in normal and nervous-system patients. According to another study, training in a virtual environment regulates the intensity of pain input from the outside at the level of the thalamus, and the thalamus before sensory input is detected in the cerebral cortex [27]. Aside from those explanations on the mechanism of pain reduction vis AR-based training, AR provides a significant reduction in bio-physiological parameters related to distress, specifically heart rate reduction [28]. It operates on psychological variables as an analgesic effect. This explains the positive effect of AR on pain reduction. In the present study, twenty-one of the twenty-four participants were women, and it seems that women perceive more nociceptive stimuli due to biological, psychological, and cultural factors [29]. Although this theory has not yet been fully explored in clinics, our study found that AR-based training is effective to considerably reduce pain sensation. The change in position each week after many repetitions facilitated the adaptation of various motions in different positions. Interestingly, this helped to increase not only the motor learning function but also the proprioception of participants. Moreover, the joint position sense plays a very important role in inducing and stimulating voluntary and involuntary motions by transmitting basic information to the motor control area, such as balance or vestibular sense [30].