In the development of the posture monitor of Solos smart glasses, research was conducted around posture and the health of the head and neck system. As may be expected, the posture of the head and the neck can play a big role in affecting the overall condition of muscles around the neck and spine, especially in people with an urban lifestyle who could spend hours each day working with computers or smartphones. Below is a summary of the different related studies, which should explain the design philosophy of the posture monitor of Solos smart glasses.
The head and neck system are a complicated set of muscles in the human body, consisting of a large array of muscles to control movement and posture of the head and neck. With that, there are many directions in which tension can be exerted to create stress for the head and the neck. That creates a set of angles with which posture can be measured with. Figure 1 shows a diagram that displays some of the said angles. As Solos smart glasses are worn in a way such that it is aligned with the direction of vision, it should provide an accurate estimate of the wearer’ gaze angle, which measures the angle at which the eyes are positioned with respect to the horizontal. However, in most studies of head and neck posture, as discussed below, the neck flexion angle remains the predominant subject of study with regards to muscle fatigue. In most use cases, it may be assumed that the two angles are associated with each other, since head movement confoundingly affects both.
Figure 1 (Ailneni, Syamala, Kim & Hwang, 2019): A diagram that depicts certain angles measured around the head and neck of a person, extracted from a study on head and neck posture.
In a typical day of person leading a cosmopolitan lifestyle, technology is involved during a large part of the day. While gadgets like smartphones and computers have had significant impact on convenience, it also leads to many drawbacks in terms of head and neck posture. Specifically, ‘text neck’ and ‘forward head posture’ are common conditions of technology users. Specifically, they refer to muscle fatigue in the neck area resulting from the constant forward bending of the neck due to the use of computers or smartphones. According to experimental research conducted by the New York Spine Surgery & Rehabilitation Medicine, the weight sustained by the neck and spine of a human body due to the head dramatically increases with the amount of neck flexion (Hansraj, 2014). Figure 2 shows a diagram, extracted from the same study, to illustrate this relationship. Based on this information, it can be quite easily inferred that the increase in loading on the neck and spine can cause stress which leads to wearing and tearing of associated muscle fibres. Ultimately, this can lead to the need for medical attention and treatment.
Figure 2 (Hansraj, 2014): Weight sustained by neck and spine against the position of the head in terms of forward flexion.
Specifically tackling the posture issues caused by smartphones in the modern day, many research projects have been done to identify the association between the duration of smartphone use and muscle fatigue around the head and neck region. An article published in the Journal of Physical Therapy Science details a research project done by the Department of Physical Therapy at Kyungnam University on continuous smartphone use and muscle fatigue (Kim & Koo, 2016). In that project, individuals had levels of muscle fatigue in the cervical erector spinae and upper trapezius muscle measured before and after continuous smartphone use for 10, 20, or 30 minutes. Results from the project showed significant difference in levels of muscle fatigue in some of the aforementioned muscle groups between individuals who continually used smartphones for 10 and 30 minutes. The research concluded with a recommendation to take some rest from using smartphones continuously after at most 20 minutes.
Another research carried out by the Department of Physical Therapy at U1 University investigated the association between neck posture in terms of neck flexion angle and the duration of continuous use of smartphones in different settings, such as standing, sitting on floor and sitting on chair (Lee, Lee & Han, 2016). Before conducting the experiment, participants reflected that, on average, they start to experience muscle pain after 10 minutes of continuous smartphone use. The results of this research are summarized in Figure 3. It can easily be seen that neck flexion increases with the duration of use of smartphone, regardless of whether the user is standing or sitting down. This result corresponds to the aforementioned research on neck flexion angle and stress applied onto the spine, which states that increased flexion causes more stress. It also further supports and provides a possible explanation for the findings in muscle fatigue and smartphone use, which suggests users to reduce continuous smartphone use.
Figure 3 (Lee, Lee & Han, 2016): Neck flexion angle against the continuous time of smartphone use
Apart from smartphone use, computer use has also been linked to strain in neck muscles. Several research studies have then been conducted to investigate the association between them. In a research study by the Department of Human Movement Studies at the University of Queensland, the relationship between the position of placement of computer monitor and head and neck posture was investigated (Burgess-Limerick, Plooy, Fraser & Ankrum, 1999). In this study, two monitor placement positions were studied, “eye-level” and “low.” Although the study did not arrive at conclusive evidence to suggest that one position was preferable, it did provide evidence that placing the monitor at a low position caused increase neck flexion, which led to a shortened period before experiencing muscle fatigue. Moreover, the study also found that the low position induced an increased in gaze direction downwards. Figure 4 provides an illustration of the average position taken by study subjects in each monitor placement conditions.
Figure 4 (Burgess-Limerick, Plooy, Fraser & Ankrum, 1999): Illustration of average position adopted in “eye-level” and “low” monitor placement positions
To study the relationship between gaze angle, also known as gaze direction, and head and neck posture, an experimental study was done by the Department of Physical Therapy at Konyang University to investigate the effect of gaze direction and deep neck flexor activation in chronic neck pain (Lee & Seo, 2020). The study involved measurements of levels of activation deep neck flexors (DNF) and sternocleidomastoid (SCM), some of the muscle groups around the neck, at different levels of gaze direction. These muscle groups were chosen as chronic neck pain patients have previously been found to have abnormalities in them. As one of the results of the experiment, the activation of SCM was found to increase significantly as gaze angle increases. When combined with the association of SCM and chronic neck pain, it can be inferred that an increase in gaze angle is associated with chronic neck pain. In fact, the research makes a suggestion that gaze angle should be kept at less than 20 degrees downwards. Along the lines of similar research, a previous literature review can be found in the International Journal of Human-Computer Interaction on health consequences of working with video displays (Aarås, Horgen & Ro, 2000). In this article, a more conservative suggestion of fewer than 15 degrees downwards was made for the optimal gaze angle. Together with the different research studies quoted above, these results tie in with the initial proposition of association between gaze angle, neck flexion angle, and muscle fatigue, which causes neck pain.
As a brief summarizing view of all the research papers referred to above, it can be inferred that increased neck flexion angles and increased gaze angles are found to be associated to chronic neck pain. Moreover, the duration of sustaining such posture is critical in causing neck pain from fatigued muscles. With that said, different studies concluded with different critical values for recommendation, both for the neck flexion and gaze angles, as well as for the length of time in using a gadget, which indirectly influences the head and neck posture. These results have been considered when devising the posture monitor for Solos smart glasses. Most concretely, the 15-degree gaze angle was chosen as a threshold to determine good or bad posture. On the other hand, although a specific relationship was not drawn between the gaze angle and neck flexion angle, observations were made to indicate an overall positive association between neck flexion angle and gaze angle, further supporting the idea of using the gaze angle to determine goodness of posture.
In our current implementation, the posture monitor can detect the inclination angle of the glasses when worn by the user, which should provide a decently accurate estimate of the gaze angle due to the way glasses are worn. When the glasses detect a prolonged period of poor posture, as determined by the inclination angle in accordance to the above quoted results, an audio reminder will be sounded to the user. The duration of period is a setting that the user may change. In the Solos AirGo app, information about the user’s posture is available for the user to review their recent statistics. These include a chart that dissects the user’s wearing pattern into good or bad posture for each day of the week. To avoid misinterpretation of data, charts will only be shown for days which the user has been wearing the Solos smart glasses for at least half the average duration of the past 7 days. Additionally, a summary provides all the relevant raw information for those who are more analytically minded. A patent for our idea and implementation of the posture monitor has been filed and is undergoing the process of review. Further development of the posture monitor is also expected to enhance the sophistication and rigor for application in improving postural health of Solos smart glasses users.
References
Aarås, A., Horgen, G., & Ro, O. (2000). Work With the Visual Display Unit: Health Consequences. International Journal Of Human-Computer Interaction, 12(1), 107-134. doi: 10.1207/s15327590ijhc1201_5
Ailneni, R., Syamala, K., Kim, I., & Hwang, J. (2019). Influence of the wearable posture correction sensor on head and neck posture: Sitting and standing workstations. Work, 62(1), 27-35. doi: 10.3233/wor-182839
Burgess-Limerick, R., Plooy, A., Fraser, K., & Ankrum, D. (1999). The influence of computer monitor height on head and neck posture. International Journal Of Industrial Ergonomics, 23(3), 171-179. doi: 10.1016/s0169-8141(97)00033-4
Hansraj K. K. (2014). Assessment of stresses in the cervical spine caused by posture and position of the head. Surgical technology international, 25, 277–279.
Kim, S., & Koo, S. (2016). Effect of duration of smartphone use on muscle fatigue and pain caused by forward head posture in adults. Journal Of Physical Therapy Science, 28(6), 1669-1672. doi: 10.1589/jpts.28.1669
Lee, B., & Seo, D. (2020). The Importance of Optimal Gaze Direction on Deep Neck Flexor Activation in Chronic Neck Pain. Healthcare, 8(4), 449. doi: 10.3390/healthcare8040449
Lee, S., Lee, D., & Han, S. (2016). The Effects of Posture on Neck Flexion Angle While Using a Smartphone according to Duration. Journal Of The Korean Society Of Physical Medicine, 11(3), 35-39. doi: 10.13066/kspm.2016.11.3.35