## 2 Materials and Methods
### Patient-Centered Rehabilitation
#### 2.4.1 Study Design, Measures, and Instruments  
In the initial screening of subject recruitment, a total number of 110 subjects were inspected in the senior care center for chronic LBP and trunk muscle fatigue. Half of them were hesitant to participate in the five weeks study and some had prior schedules due to which they refused to take part in the study. Moreover, some subjects had other major chronic conditions due to which they were not able to participate in the exercise training. Therefore, it was difficult to find only those subjects who were willing to voluntarily take part in the study and those who had only chronic LBP or other trunk muscle fatigue. Finally, we recruited a total of 30 subjects who voluntarily agreed to participate in the study. The inclusion criteria included elderly patients with LBP or trunk muscle fatigue. The exclusion criteria included a history of stroke and low back, hip, or leg surgery. The subjects underwent a medical checkup and radiographic examination using X-ray imaging in a local clinic. They had major and minor spinal deformations based on the medical reports. Among them, 18 subjects who only experienced LBP for a mean period of 2.3 years were chosen for this study. Subsequently, they were equally and randomly divided into two treatment groups: the control and experimental groups. The control group performed the exercise training in the level-standing position, and the experimental group completed the exercise training in the incline-standing position. Over the course of the study, two subjects withdrew from each group because of health problems (n = 1) or not following up (n = 1). Thus, 8 subjects in the experimental group and 8 subjects in the control group were included in the current analysis.  
We arranged the main exercise training and experiments to last 5 weeks. The experimental group performed standing exercise training with the exercise object, and the control group completed the exercises without the object. Both groups performed training for 25 min daily, except on Saturdays and Sundays, with a 7-min break, for 5 weeks.  
The LBP was evaluated at the end of each day's exercise training based on subjective response measures--feelings of pain in the lower back trunk. The LBP was measured using the Wong-Baker FACES Pain Rating Scale. This scale features faces ranging from a happy face at 0 indicating \"no pain\" to a crying face at 10 indicating \"worst pain.\" The scale was obtained from the Wong-Baker FACES Foundation (For Wong-Baker Faces, [[https://wongbakerfaces.org/](https://wongbakerfaces.org/)]([https://wongbakerfaces.org/](https://wongbakerfaces.org/)), accessed on 7 April 2022) in the Korean language.  
To measure the muscle activation level of the back trunk during exercise, an electromyography (EMG) device (sEMG-4, PolyG-A, LAXTHA Inc., Daejeon, Republic of Korea) was used for recording EMG signals during the 5 weeks. Two pairs of Ag/AgCl surface electrode disks with a diameter of 11.4 mm were placed on the specified muscles at standardized sites after cleaning with ethanol. For the LD muscle, the electrode was placed 4 cm below the inferior angle of the right scapula. For the LES muscle, the electrode was placed on the right side of the vertebral column (L5) that extends alongside the lumbar portion of the spine. A reference electrode was placed over the seventh cervical vertebrae of the spinous process.