# Analysis of Available Solutions for the Improvement of Body Posture in Chairs
## 2 State of the Art  
There are a few ways to determine whether a person has a good or poor posture while sitting, as well as ways to correct it. Most solutions require the usage of sensors (force-sensitive sensors, flex sensors, etc.) but others favor a visual inspection system. The solutions found can be invasive or non-invasive. For example, harnesses and the Upright Go [11] are an invasive solution for the correction of poor posture. While these are quite a direct approach and can provide good results, most users might find them undesirable as they could feel unpleasant or constricting. In order to eliminate such problems, non-invasive solutions have been created. Some of these include the addition of sensors in chairs to determine the body's posture based on the center of gravity. Others use a camera, which visually identifies the posture adopted. Posture-sensing chairs use sensors placed strategically in the seat and backrest of the chair. The sensors can be force-sensitive resistors, pressure cells, flex sensors, temperature sensors, acoustic sensors, and ultrasonic range sensors. As mentioned previously, most solutions are based on the usage of sensors, more specifically, force-sensitive resistors (FSR). In [PERSON] et al. [12], the solution presented consists of 19 FSRs that are in a near-optimal placement in the seat and backrest of an office chair. Their prototype is able to recognize 10 different body postures with an accuracy of 78%. The 10 postures were: left leg crossed; right leg crossed, leaning left; leaning back; leaning forward; leaning right; left leg crossed, leaning right; seated upright; right leg crossed; slouching. In [PERSON] et al. [13], six FSRs are placed on the seat of the chair. The seven recorded postures were: upright, reclined, torso bent forward, torso inclined laterally to the right, torso inclined laterally to the left, upright with the right leg crossed over the left and upright with the left leg crossed over the right. The system's accuracy in classifying the seven different body postures reached 81%. Another example that uses FSRs can be seen in [PERSON] et al. [14]. With a total of eight FSRs, four on the seat and four on the backrest, it was possible to detect eight states: body leaning right, leaning left, body leaning back, sitting upright, right leg crossed over left, left leg crossed over right, sitting forward, and no contact. Others have decided to use pressure cells. For example, in [PERSON] et al. [2], four pressure cells were placed on the seat of a chair. The placement of the cells was based on an anatomical approach. Using these sensors, it was possible to detect 10 positions: upright; slouching; leaning forward; leaning back; leaning left; leaning right; left leg crossed over right; right leg crossed over left; left leg crossed over right and leaning right; right leg crossed over left; leaning left. Another example, found in [PERSON] et al. [15], uses 12 pressure sensors in the seat and 8 in the backrest. It also has two ultrasonic sensors, placed in the shoulder blades area, with the purpose of detecting/measuring the distance between the chair and the head and neck. The goal of this device was to identify whether the posture of the user is good or not, with an accuracy of at least 70%. Body posture can also be determined using flex sensors. For example, in [PERSON] et al. [16], by using six flex sensors, it was possible to determine seven sitting postures. Those were: straight; left recline; right recline; lounge; lean backwards; left leg crossed; right leg crossed. Their estimated accuracy for the device is around 97%. Another way to determine the body posture of a sitting person is to use temperature sensors and acoustic sensors. This type of solution works by detecting the body's temperature in order to classify the body posture. The acoustic sensors should be able to detect movement when the user is changing positions.