# HAL Training in Spinal Cord Injured Patients: A Narrative Review of 10 Years Experience
## 3 Results
### Clinical Trials
These certainly surprising results indicate that the initial functional gain after 3 months of daily HAL training was stable and consistent over a 1-year period [13]. A completely new approach to HAL therapy was described by [PERSON] et al. [14] in their 2017 study. HAL support is predominantly based on EMG signals from the lower extremity or weight shift over the sensor shoes. Since such muscle signals are usually undetectable in patients with complete paraplegia or tetraplegia and controlled loading of the feet is rare, the researchers decided to use upper extremity muscle activity as a trigger of lower extremity movement. This is based on the assumption that the lower extremities move synchronously and almost simultaneously with the contralateral upper extremities during natural locomotion [14]. The authors hypothesized that triggering lower limb motion by upper limb muscle activity was feasible to generate voluntary gait and furthermore, that this may activate paralyzed lower limb muscles. Muscle activities from the anterior and posterior deltoid were used for contralateral hip flexion and extension and activities from the biceps and triceps brachii for contralateral knee flexion and extension [14]. Patients underwent ten sessions of walker assisted HAL training protocol for 60-90 min (net HAL training time 30 min) once or twice a month (\(n=2\)) or twice a week (\(n=2\)). In two patients who were able to flex their hips (before or along the intervention) a knee extension training using hip flexor activation was performed additionally in order to regain active knee extension. EMG was used to evaluate muscle activity of the tensor fasciae latae (TFL) and quadriceps femoris (Quad) [14]. Prior to intervention none of the participants showed apparent activation in Quad and only one in TFL. However, gait phase dependent activity of the lower limb muscles was seen during voluntarily triggered ambulation driven by upper limb muscle activities and in some cases active contraction in Quad was observed after knee extension session using the hip flexor as trigger [14]. Therefore, the authors conclude that this method is a feasible option for patients with severe paraplegia or tetraplegia. Although these results are certainly exciting, it is difficult to generalize. In this study, only four patients were examined and they had different training frequencies. Furthermore, in two of the four patients, the upper body controlled training was started after three and five sessions, respectively, and another mode of the HAL accompanied with heavy assistance from three therapists was used beforehand to familiarize the patients with the use of such a device. One of the four patients received additional physiotherapy during the training phase. Nevertheless, with this study the authors contribute to the understanding of possible applications of the HAL even in severely injured patients. In addition to the results already mentioned, the patients improved their walking distance and three out of four patients showed improvements in Ashworth score, which is in line with the results of other studies [9; 11]. A question similar in approach to [PERSON] et al. [12] was pursued by [PERSON] et al. [15], who asked whether HAL training is appropriate for all severities of SCI. They stated that in most of the preliminary studies patients already had a certain walking function before the treatment participated. They set out to investigate the effect of training in relation to the severity of SCI. For this purpose, 20 chronic patients were recruited and divided into a low walking ability group (\(n=8\)) and a high walking ability group (\(n=12\)) based on their WISCI II scores at baseline. Twenty training sessions with a frequency of 2-5 per week were performed on the treadmill. Gait performance on treadmill (speed, distance, and time) was significantly lower in the low walking ability group while perceived exertion was higher.