**2.1. Biofeedback**

integration of behavioral genetics, neuroscience and peer influence research. While most previous research emphasize on the dynamic, reciprocal associations between selection and socialization in adolescent peer relations, their review focuses predominantly on their socialization processes as the mechanisms in the past decade have continued to vary considerably

It is difficult to detect and measure peer effects precisely. Peer effects are the average intragroup external effects which are identical on all the members of a given group. Due to the disaggregation and availability of data, the group boundaries for such peer effects are often random and varying. Calvó-Armengol et al. [21] propose a peer-effect model to relate analytically equilibrium behavior to network location. Their results show that the outcome of each individual embedded in a network is proportional to her Katz-Bonacich centrality measure [22, 23] at the Nash equilibrium. For each individual, the Katz-Bonacich centrality measure considers both her direct and indirect friends but puts less weight to her distant friends.

The term *social network* refers to the web of social relationships that surround individuals [24, 25]. Social networks are a social structure of nodes that represent individuals and the relationships between them within a certain domain. This research adopts social networks as the linkages between students. The closeness of students is embedded in an informal group where group members can provide social functions like informational, instrumental, emotional and appraisal supports to individuals. Social supports and collaboration can be very constructive to physical, mental and social health of individuals. The wide use of smartphones and social networking apps offer opportunities for the development of innovative interventions to promote physical activity. Ayubi et al. [26] develop a persuasive and social mHealth application designed to monitor and motivate users to walk more every day. Collaborative social networks open up new ways to work with peers and improve engage-

Publics, where norms are set and reinforced, play a crucial role in the development of individuals. However, society's norms and rules only provide the collectively imagined boundaries. People, especially teenagers, learn through action, not just theory. They are also tasked with deciding how they want to fit into the structures that society provides. Their social identity is partially defined by themselves and partially defined by others. The answer to why students joined social network sites is usually simple: "That's where my friends are." The rapid adoption of social network sites by teenagers in the United States and in many other countries around the world has drawn much research attention [28]. Centola [29] studied the spread of health behaviors through artificially structured online communities and the effects of network structure on diffusion. His research reveals that when participants receive social reinforcement from multiple neighbors in the social network, individual adoption is much

Social presence is shown to have an effect in different virtual learning environments [30]. Liccardi et al. demonstrated the social dimensions of a collaborative learning network, its formation, its presence and its influence on different social networks in education [31]. They found that group composition may affect how efficiently a group achieves its set goals. It is optimal that there are both goal-oriented group members and socially oriented people within

due to new mobile and social network technologies.

40 Biofeedback

ment and effectiveness to activities [27].

more likely.

Biofeedback is an autonomic feedback mechanism that gains awareness of physiological functions from the information measured by instruments [32]. Biofeedback monitors and uses physiologic information (e.g., hearing, vision, feeling) to teach people to change specific physiologic functions (e.g., posture) accordingly. A biofeedback mechanism involves measuring biomedical variables and relaying them to the user using either direct feedback regarding the measured variables with a numerical value displayed, or transformed feedback where the measured variables are transformed into an adaptive auditory signal, visual display or tactile feedback method. The majority of biofeedback therapy has focused on the treatment of upper limb and lower limb motor deficits in neurological disorders.

**Figure 1** depicts the biofeedback posture training loop, where head, neck and lower back posture is monitored and biofeedback to the human sensory nervous system with sound, light and vibration in order to notify the people to improve her head, neck and lower back posture accordingly. In the biofeedback process, posture signals are first measured by sensory and filtering devices where filtered sensor data are generated and sent to posture estimator to construct the corresponding posture angles. The posture angles are used by fuzzy logic trainer to diagnose the posture and determine what alters (sound, light, or vibration) to biofeedback to the human sensor nervous system.

Many physiological landmarks such as tragus, canthus, eye socket, nation, or infraorbital notch have been used in measuring head/neck posture. Sitting is a common aggravating factor in neck, shoulder and low-back pains. Head/neck posture and cervical flexion are a complicated mechanism involving the skull and eight joints of C1 through T1 vertebrae. The head/neck angle often referred to as the degree of forward or peering head posture, or neck protraction is typically defined as the angle between vertical and a line connecting C7, T1, or the acromion to various skull landmarks. The C6-C7 vertebrae are important because they support and stabilize the head during its movement. When people sit in a good posture, the line of gravity should pass through the C6-C7 vertebrae. The C7-tragus angle, also known as the cranial-vertebral angle, is the angle between a vertical line passing through C7 and the line from C7 to the tragus. The lumbar angle (T10-L3 and L3-S2) [38] is typically defined to measure the ability to reliably position people into a neutral lumbar spine sitting posture.

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In a study comfortable head and neck posture at computer workstations, Ankrum and Nemeth [43] suggested that the mean observed head tilt (Ear-Eye Line 7.7° above horizontal) and head/neck posture of 43.7° in C7-tragus against vertical are more flexed. Breen et al. [11] measure head and neck angle by placing an accelerometer device at the C7 vertebrae directly,

As the state of head/neck posture is unobservable, in this research, we adopt the C7-tragus and L3-S2 angle, as the metrics to measure head-and-neck and lumbar postures, respectively, as depicted in **Figure 2**. A comfortable head-and-neck angle is about 30° in a normal sitting posture and about 40° in using computer. A posture below 25° or beyond 50° is considered poor and need-to-be-corrected. A comfortable lumbar angle is about 5° in normal sitting pos-

as measuring the cranial-vertebral angle.

ture. A posture below 0° or beyond 15° is considered bad.

**Figure 2.** Posture monitoring (left: head/neck, right: lumbar/low back).

**Figure 1.** The CSPT biofeedback posture training loop.

Biofeedback is one of the popular clinical therapy approaches in healthcare. It aims at helping people take responsibility for the cognitive, emotional and behavioral changes needed to affect healthy physiologic change. Biofeedback is a learning process where many instruments are used to monitor the physiologic processes, measure and transform the measurement data into auditory, visual, or vibrating signals in a simple, direct and immediate way. In the biofeedback process, physiologic information is monitored and fed back through the biofeedback instruments. Biofeedback guided by the information provided by the biofeedback instruments is to enable and change the physiologic process of the people.

A well-designed biofeedback mechanism should consider the following conditions:


In this chapter, we adopt sounds, music, flashing light and vibration functions of smartphones in design of our biofeedback mechanism so that teens can receive timely notations when their bad posture is detected.

#### **2.2. Posture monitoring**

The purpose of posture training is to keep the body at its *neural* position. Several attempts have been made to define neutral of the head/neck and lumbar/low-back regions [33–42]. Many physiological landmarks such as tragus, canthus, eye socket, nation, or infraorbital notch have been used in measuring head/neck posture. Sitting is a common aggravating factor in neck, shoulder and low-back pains. Head/neck posture and cervical flexion are a complicated mechanism involving the skull and eight joints of C1 through T1 vertebrae. The head/neck angle often referred to as the degree of forward or peering head posture, or neck protraction is typically defined as the angle between vertical and a line connecting C7, T1, or the acromion to various skull landmarks. The C6-C7 vertebrae are important because they support and stabilize the head during its movement. When people sit in a good posture, the line of gravity should pass through the C6-C7 vertebrae. The C7-tragus angle, also known as the cranial-vertebral angle, is the angle between a vertical line passing through C7 and the line from C7 to the tragus. The lumbar angle (T10-L3 and L3-S2) [38] is typically defined to measure the ability to reliably position people into a neutral lumbar spine sitting posture.

In a study comfortable head and neck posture at computer workstations, Ankrum and Nemeth [43] suggested that the mean observed head tilt (Ear-Eye Line 7.7° above horizontal) and head/neck posture of 43.7° in C7-tragus against vertical are more flexed. Breen et al. [11] measure head and neck angle by placing an accelerometer device at the C7 vertebrae directly, as measuring the cranial-vertebral angle.

As the state of head/neck posture is unobservable, in this research, we adopt the C7-tragus and L3-S2 angle, as the metrics to measure head-and-neck and lumbar postures, respectively, as depicted in **Figure 2**. A comfortable head-and-neck angle is about 30° in a normal sitting posture and about 40° in using computer. A posture below 25° or beyond 50° is considered poor and need-to-be-corrected. A comfortable lumbar angle is about 5° in normal sitting posture. A posture below 0° or beyond 15° is considered bad.

**Figure 2.** Posture monitoring (left: head/neck, right: lumbar/low back).

Biofeedback is one of the popular clinical therapy approaches in healthcare. It aims at helping people take responsibility for the cognitive, emotional and behavioral changes needed to affect healthy physiologic change. Biofeedback is a learning process where many instruments are used to monitor the physiologic processes, measure and transform the measurement data into auditory, visual, or vibrating signals in a simple, direct and immediate way. In the biofeedback process, physiologic information is monitored and fed back through the biofeedback instruments. Biofeedback guided by the information provided by the biofeedback

instruments is to enable and change the physiologic process of the people.

• whether the individual is capable of responding;

• how the individual is encouraged to learn; and

• how the individual is inspired to learn;

**Figure 1.** The CSPT biofeedback posture training loop.

42 Biofeedback

bad posture is detected.

**2.2. Posture monitoring**

A well-designed biofeedback mechanism should consider the following conditions:

• whether the individual is given correct information about the results of the learning effort.

In this chapter, we adopt sounds, music, flashing light and vibration functions of smartphones in design of our biofeedback mechanism so that teens can receive timely notations when their

The purpose of posture training is to keep the body at its *neural* position. Several attempts have been made to define neutral of the head/neck and lumbar/low-back regions [33–42].

**Figure 3.** Posture training devices (left: head/neck training headset, right: lumbar training belt).

Let *<sup>G</sup>* <sup>=</sup> [ *Gx*′ *Gy*′ *Gz*′ ] *T* be an acceleration vector, where *Gx*′ , *Gy*′ and *Gz*′ represent the acceleration in *x*′ -, *y*′ - and *z*′ -axis, respectively, and *Gx*′ *Gy*′ *Gz*′ <sup>≠</sup> 0. The tilt angle along the *z*′ -axis, *ρ*, can be calculated by the following equation:

$$\rho = \cos^{-1}\left(\frac{G\_{\ddagger}}{\sqrt{G\_{\ddagger}^2 + G\_{\ddagger}^2 + G\_{\ddagger}^2}}\right) \tag{1}$$

filtering device monitors real-time head/neck and lumbar posture and determines head craning forward or hanging downward as well as the forward low back. Using the biofeedback process with sound, light, or vibration, people receive alert and warning when their head/ neck or lumbar posture is determined as bad. The biofeedback mechanism guides the people

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Operation scenarios of the collaborative, social-networked posture training (CSPT) system are summarized into the following five stages: *Preparation*, *Measuring*, *Posture Control*, *Analysis*

A subject wears the posture training headset and the lumbar belt, invokes the CSPT App and

The posture monitoring sensors start to monitor the posture status and send streaming data

The App or gadgets biofeedback to the subject with sound, music, vibration, or flashing light, when poor posture is determined. The subject responds and corrects the head/neck or lower

Posture data are compiled, transferred and stored in the cloud for further analysis. The subject can query and review their own historical behaviors and analytic information in their

Notifications of posture alerts and analytic data can be shared to subject's parents, guardian, or friends. Without violating privacy and security considerations, the data and analytics stored in the cloud can be shared to doctors, researchers, or public health workers to improve

The collaborative, social-networked posture training (CSPT) framework is designed and based on three fundamental technologies of (1) real-time posture measuring, (2) biofeedback control and (3) social networks and collaboration. Monitoring and measuring of head/neck and lower back postures require techniques of sensing the movement and measuring the displacement of head/neck and lumbar positions in real time, with respect to their neural positions. Transformation among many coordinate systems is needed to reflect head/neck

There have been some researches attempting to define the normal and correct posture of head, neck and shoulder, from various different points of view [45–47]. The idea along the neutral spine position—ears aligned with the shoulders and the shoulder blades retracted—is mostly used by many researchers and practitioners. This research defines the head/neck posture by

to identify, change and correct the head/neck or lumbar posture to right positions.

and *Sharing*, whose details are described as follows:

of posture angles to the receiving CSPT App or gadgets.

places the smartphone in the lumbar belt.

back postures to the good positions timely.

Stage 1. *Preparation*.

Stage 2. *Measuring.*

Stage 3. *Posture Control.*

smartphone or smartwatch.

healthcare and welfare.

and lower back postures.

Stage 4. *Analysis.*

Stage 5. *Sharing.*

With the accelerations measured and provided by the accelerometer, Eq. (1) can calculate the tilt angle of the sensor with respect to the earth.

The calculated tilt angle needs to be further transformed into the coordinate system (*x*, *y*, *z*) of the head, with its origin at the center of the head in **Figure 1**. The sensor tilt angle is then converted into the head/neck posture angle. The lumbar angle can be determined along similar calculations. The stream of the posture angles forms a set of time-series data, which are processed by the meta-heuristic based on Kalman filter and fuzzy logics algorithms [44]. Rather than placing an accelerometer in the C7 vertebral only such as in [11], our innovative design puts the posture angle sensor along with the C7-tragus line. The posture angle sensor is fixed with a fine plastic enclosure that is attached to a lanyard and connects to a creatively designed earhook in both sides of the ears. **Figure 3** shows the wearable training headset.
