ONE GAIT CYCLE

The actual duration of these gait cycle intervals depends on the walking velocity of the age and health status of a person. The normal walking speed for a healthy elderly is approximately 1.12 m/s (S. Studenski et al., 2011). Figure 3.5 depicts the timing diagram for temporal characteristics which describe the situation either the foot having contact or no contact with the ground in all phases in a gait cycle.

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In the timing diagram above, one clock cycle is equivalent to 10% of the gait cycle. At normal walking rate, single support limb and double support limb periods represent 40% and 20% (DS1 and DS2) of the gait cycle, respectively, while the second double limb interval (DS3) corresponds with the beginning of the next gait cycle. Total ground contact for both feet in one gait cycle is 60%, which is equivalent during the stance phase period. The single limb support time is equal to the swing time as they occur at the same time (see Fig. 3.5). In addition, the information of spatial characteristics of the gait cycle is pretty important as parameters need to be considered as a cut-off value in the process of designing an obstacle detection system. The step width and step length are the two examples of spatial characteristics in stride length that are equivalent to one gait cycle. One gait cycle is comprised of two steps as shown in Figure 3.6.

Figure 3.6:Illustration of one gait cycle (M. W. Whittle, 2007).

A gait cycle is described as the period from the initial contact of one limb to the point of initial contact of the same limb, and also known as stride length. The step width is

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Step width

determined as the medial–lateral distance between the locations of sequential left and right heel-strikes as illustrated in Figure 3.7.

Figure 3.7:Illustration of a step width (T.M. Owings and M.D. Grabiner, 2003).

The step width varies depending on the age of the individual. Based on observation, the elderly had a wider step width compared to adult people (P. Robert et al., 2006). Scientific research indicates that the mean value of step width is between 7.4cm to 11.2cm (J. L. Helbostad and R. Moe-Nilssen, 2003; D. M. Wert et al., 2010). Established research shows that the step width ranges between 10.1 cm to 12.2 cm (J. H., Hollman et al., 2011). The measurements were taken from 294 older men and women, and this reflects a reliable step width value for the elderly. However, the variability of the step width depends on the style of walking and size of the foot. The largest foot width reported is 10cm, which is equivalent to a step width of 22cm (J. S. Brach et al., 2001). Meanwhile, the step length refers to the distance from a point of contact with the ground of one foot to the following occurrence of the same point of contact with the other foot as shown in Figure 3.8.

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Step length

Figure 3.8:Illustration of step length in gait analysis.

The variability of step length depends on the age and leg length of a person. In the biomechanical study, the step length is proportional to the user’s leg and height (V. Renaudin

et al., 2012). The average step length of an active elderly woman is between 64.6cm to 66.3cm (B. S. Moreira et al., 2012; A. Zijlstra et al., 2008; B. S. Moreira et al., 2012), while the elderly man is between 85.6cm to 86.5cm (B. W. Schulz, 2012; Y. Taniguchi et al., 2012).

3.3 Specification of the Detection Area

Generally, the determination of a single walking path width is a very important aspect and considered as a key factor to ensure a reliable performance of the designed obstacle detection system for the elderly. A prior literature survey on gait parameters is necessary to justify the efficient path width and entire detection area for the system. The stride length is an important gait parameter which determines a suitable path width and warning consideration when the obstacle is detected in a single walking. The stride length is a combination of step width and step length which has been discussed in the previous section. Figure 3.9 represents the configuration of step width in a single completed stride length occurrence (T.M. Owings and M.D. Grabiner, 2003).

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Figure 3.9:Illustration of step width in a single stride length.

A typical range of step width for the elderly is between 7.2 cm to 12.2 cm (J. L. Helbostad and R. Moe-Nilssen;D. M. Wert et al., 2010;J. H. Hollman et al., 2011). The largest foot width reported is 10cm which is equivalent to a step width of 22cm (J. S. Brach et al., 2001). In addition, according to a report from the Department of Transport of Western Australia (Department of Transport of Western Australia, 2012), a minimum side clearance of 0.5m is required between the path edge and adjacent hazards for shared paths. In isolated cases, (M. Tinetti, 1986) observed that an estimation walking path width required for the elderly with a frontal gait disorder is 30cm. Based on these evidences, 0.5m is satisfactory for a single path width. The path width determination is an important criterion in determining the number of sensors that could be used for an optimum detection of 0.5m width. In our work, the combinations of ultrasonic and infrared sensors are the best option to detect all types of obstacle within the setting of pathway width. According to the technical specification of the sensors (Sharp Microelectronics, 2006; MaxBotix Inc., 2007), the response time of ultrasonic sensor is approximately 50ms where it is 38ms ±10ms for infrared sensor. Since both sensors indicate fast processing time compared to the typical walking speed, which are 1.5m/s and 1.0m/s to

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