**4. Kinetic and kinematic indices**

The stability index was developed with two parameters—relative standing time and relative standstill time [14]. The relative standing time was defined as a ratio between the successful standing time and the requested standing time. The successful standing time was measured as the total standing time before the subject failed to maintain stability, allowing the non‐ dominant, lifted limb to touch the force plate. The relative standstill time was defined as a ratio between the sum of standstill time and successful standing time. The standstill time was the summation of the temporal segments, where the three‐dimensional rotation of the tested axis was below threshold (5°).

In **Figure 2**, the distribution of the normalized standing time was plotted with the corre‐ sponding relative kinematic index for the core spine model between the control group and the recurrent LBP group. The data obtained from five subjects were selected as examples

Several studies have used the one‐leg standing test to investigate postural control using dif‐ ferent outcome variables [7, 13, 47]. The one‐leg standing test can be divided into two phases: the dynamic phase and the static phase. The dynamic phase is defined as a rapid decrease of force variability during the first 5 seconds (s) of the test. The static phase is defined as the maintenance of a certain level of force variability. One study, which investigated the first 5 s of a 25 s duration test (dynamic phase), concluded that the first few seconds of the one‐leg standing test pose the greatest challenge to postural steadiness [48]. They concluded that if participants were unable to perform one‐leg standing for at least 5 s, they were at an increased risk for injurious falls. Other studies have investigated the static phase. High vari‐ ability during the first 5 s of the static phase of the one‐leg standing test was reported, which could potentially be caused by muscular or postural adjustments [7, 14]. Based on these find‐ ings, it might be possible to analyze the first 5 s increments of the static and dynamic phases of postural stability to discover different aspects of sensorimotor function that older adults

It has been reported that impaired back muscle function may lead to an inability to adopt postural control strategies focused on increasing strength and self‐efficacy in older adults with LBP [49, 50]. These studies suggested that impaired back muscle function may lead to an adaptation of postural control strategies with the primary purpose of preventing pain and decreasing mobility of the painful region. By contrast, longer one‐leg standing duration in the control group can be explained by enhanced motor learning due to greater ability to perform

Other studies supported the reorganization of trunk muscle representation at the motor cor‐ tex in individuals with recurrent LBP [51, 52]. Their results suggest that this reorganization is associated with deficits in postural control, which persist after the training effect takes place as LBP becomes chronic or recurrent. Eventually, these learned strategies become automatic

The stability index was developed with two parameters—relative standing time and relative standstill time [14]. The relative standing time was defined as a ratio between the successful standing time and the requested standing time. The successful standing time was measured as the total standing time before the subject failed to maintain stability, allowing the non‐ dominant, lifted limb to touch the force plate. The relative standstill time was defined as a ratio between the sum of standstill time and successful standing time. The standstill time was the summation of the temporal segments, where the three‐dimensional rotation of the tested

In **Figure 2**, the distribution of the normalized standing time was plotted with the corre‐ sponding relative kinematic index for the core spine model between the control group and the recurrent LBP group. The data obtained from five subjects were selected as examples

functional activities and implement more functional postural control strategies.

defense mechanisms to prevent pain and further injury [15, 52].

**4. Kinetic and kinematic indices**

axis was below threshold (5°).

with LBP use to enhance pain‐avoiding strategies.

200 Innovations in Spinal Deformities and Postural Disorders

**Figure 2.** A: Distribution of normalized standing time (x‐axis) and relative kinematic index (y‐axis) of body regions and corresponding three‐dimensional angle (Rxyz) from control group (diamond) and LBP group (open dot). B: Examples of Rxyz traces from A. Subject 25 had stable and long duration, while subject 28 had unstable long duration. Subject 18 had short duration with stable balance and subject 31 had relatively short duration with unstable balance. Subject 29 had longer duration and more stable balance than subject 31. Threshold (dot) and baseline (solid) are plotted for each trace.

of the normalized standing time, and the relative kinematic index was compared with the corresponding subjects' *Rxyz* values. The analysis time window excluded the initial transition time (5 s) from the test [14].

Therefore, the rotational angular displacements were more important than translations during the test. The operational definitions for the terms utilized in this study are included as follows:


**Figure 3.** The rotation angle of the core spine computed from kinematic markers. For computing stability index, initial transition time (5 s) was excluded. Out of 25 s requested holding time, successful holding time (duration) was measured as the total duration until subject fail to stand on one leg (large arrow). The kinematic stability was measured as the square root sum of axial angle subtracted from its own mean value during successful holding time (see equation).

• The dynamic postural steadiness index (DPSI): The DPSI (4) was based on the kinetic data, which was calculated for three principal directions and was reported as a sen‐ sitive measure index. The DPSI is a composite of the medio‐lateral steadiness index (MLSI; 1), anterior‐posterior steadiness index (APSI; 2), and vertical steadiness index (VSI; 3), which are mean square deviations assessing fluctuations around a zero point, rather than standard deviations assessing fluctuations around a group mean. The sta‐ bilization time was also determined as an objective postural control measure by using three indices of analysis based on the resultant GRF. The MLSI and APSI assessed the fluctuations from a zero point along the frontal and sagittal planes of the force plate, respectively. The VSI assessed fluctuation of the subject's body weight to normalize the vertical scores for standardization of the vertical GRF along the transverse plane of the force plate. This measure allowed comparison of individuals with different body weights (mass).

The force space. Thus measure among the comparison with uninteresting body weights (mass).

$$\text{MLSI} = \sqrt{\left[\frac{\Sigma(0-\mathbf{x})^2}{\text{number of data points}}\right]} \tag{1}$$

The Quantified Indices for Compensatory Patterns for Low Back Pain and Outcome Measures http://dx.doi.org/10.5772/intechopen.69910 203

$$
\text{http://www.org/10.5772/ntetch.org/69910}
$$

$$
\text{APSI} = \sqrt{\left[\frac{\Sigma \left(0 - y\right)^2}{\text{number of data points}}\right]} \tag{2}
$$

$$\text{AFSI} = \sqrt{\left[\frac{\text{number of data points}}{\text{number of data points}}\right]} \tag{4}$$

$$\text{VSI} = \sqrt{\left[\frac{\Sigma \left(\text{body weight} - z\right)^2}{\text{number of data points}}\right]} \tag{5}$$

$$
\mathbf{V} \times \mathbf{u} = \sqrt{\left[\begin{array}{c} \text{number of data points} \\ \end{array} \right]} \tag{2}
$$

$$
\text{DPSI} = \sqrt{\left[\begin{array}{c} \Sigma \left(0 - x\right)^{2} + \Sigma \left(0 - y\right)^{2} + \Sigma \left(\text{body weight} - z\right)^{2} \\ \text{number of data points} \end{array} \right]} \tag{4}
$$

The outcome measures included one‐leg standing time, DPSI (composite of MLSI, APSI, and VSI), and stabilization times. In this way, postural stability might be quantified during the one‐leg standing test with the underlying premise that dynamic postural stability depends on lower limb kinematics.
