## 3 Results
### Study Characteristics
#### 3.2.4 Rehabilitative Approaches
Unstable surfaces, balance pads, and Swiss balls are tools that have proven useful for the training of balance and trunk control. Although one study on stroke found that core stability training on both stable and unstable surfaces is more beneficial than conventional training, with no differences due to the support surface [33], other studies found that training on unstable surfaces is more beneficial for trunk control and sitting balance [35; 40; 63; 64; 66; 71], gait [35], and standing balance [71]. In addition, training on unstable surfaces led to greater improvements in balance and gait in people with chronic SCI [32]. Another useful tool commonly found in clinics is the cycle ergometer, which is useful not only for limb rehabilitation but also for improving trunk control following stroke and SCI. In contrast, within the technologies used in the selected articles, we can distinguish technologies used for electrical stimulation (ES), systems that enhance different types of feedback for improving performance, and robotic training technologies. ES is widely used in SCI, with beneficial effects on trunk control and trunk muscles' activity [120; 123; 124]. It has also been proven to be beneficial for stroke patients, as it improves both trunk control and standing balance [69; 102]. In addition, [PERSON] et al. [102] showed that the maximal effect was achieved when coupled with core muscle training. Several studies have highlighted the potential to enhance training effectiveness through the implementation of specialized programs that incorporate diverse forms of feedback. More precisely, training programs that integrated exercises based on visual, audiovisual,  
Figure 2: Summary of the results. and combined visual and proprioceptive feedback demonstrated superior improvements in trunk control, core stability, and balance compared to conventional training approaches. [PERSON] et al. [56] proposed a smartphone app that could also be used from home and not only in clinical settings. Real-time visual feedback was also provided during virtual reality training (VRT). This approach enhances their appreciation of these exercises and increases their motivation. Six articles that were included in the review proposed this approach. Specifically, VRT provides feedback based on the performance of the subject. The studies included here used either Kinect [25; 27; 48; 99] or the Nintendo Wii [96] to monitor the subject's performance, and only one of them provided a virtual experience with an immersive virtual reality system [27]. Despite the different methods, there is agreement on the effectiveness of adding VRT to conventional training to improve trunk control, sitting balance, standing balance, and gait [47; 107]. Finally, some recent studies have evaluated the effectiveness of robotic training in comparison to conventional approaches. The robotic devices used in the studies selected in this review were very diverse. Two studies used the Spine Balance 3D system [73; 93], which comprises two wireless ground force plates, a trunk sensor, a visual feedback monitor, and a tilting main body capable of tilting in eight distinct directions [130]. During training, the subjects were securely fastened at the lower part of their bodies, allowing the apparatus to tilt strategically. This controlled tilting prompted the subjects to engage and strengthen their core muscles. Training with this system led to greater improvements in terms of gait and the control of trunk muscles [73; 93] and led to results comparable with training performed with the Biodex Balance system in terms of sitting and standing balance [93]. One study used the Space Balance 3D system [53] (which is based on the same concept as the previous device) and proved that after training with such a device, stroke subjects reported higher improvement in standing balance, trunk control, and control of trunk muscles than achieved via conventional training. The other robotic devices included in the studies in this review were based on movable chairs.