Introduction
he world’s elderly population has grown significantly over the past few decades [3, 2, 1] and is expected to increase in the future [2]. With aging, all factors involved in balance, including walking speed [1], are affected [4]. About 27%-65% of the elderly experience falls at least once a year [5, 6]. Fear of falling is the most common fear among the elderly [7، 8]. Several interventions have been used to maintain and improve walking speed and balance in the elderly. These interventions include vestibular neurosurgery, physiotherapy, exercise therapy, orthosis interventions, and using special shoes [11, 12 ,13 ,14, 15]. Since the feet have direct contact with the ground during walking, any change in the space between the sole and the ground can affect the postural stability of people [9, 10]. Many features in shoe design can affect balance and walking speed [11, 12 ,13]. In assessing the characteristics of the sole of the shoes, one of the common interventions used for a wide range of problems and target groups is the addition of rocker soles to the shoes [14, 15]. Other rockers have various therapeutic effects on the target groups [19]. The geometric characteristics of toe rockers in the anterior part are determined by three variables of apex angle, apex position, and rocker angle [21]. The rise and function of the apex change the rate of movement of the lower extremity joints, especially the ankle, walking speed, kinematic gait, and the patterns of rocker during the gait cycle. In this way, a change in the apex angle and position can improve or weaken these variables [21, 22] and, thus, affect people's balance and walking speed.
In examining the characteristics of the toe rocker, Chapman’s study showed that the use of a rocker with an apex angle of 95-90 degrees had good equilibrium effects on the study groups [16]. Meyer et al. and van Schie et al.’ studies showed that, for optimal balance performance, the most effective apex position is at 55%-65% of the shoe length [17, 18]. In another study, the effect of rocker angles on the degree of dorsiflexion and toe clearance was investigated. The results showed that, regardless of the ground inclination, shoes with toe rockers at angles of 10-15 degrees compared to other rockers significantly increased toe clearance in the elderly and consequently reduced the risk of falling [19].
Given the growing rate of the aging population and the increasing injuries caused by poor postural balance, a study in the field of balance and walking speed of the elderly can be of great value to this group. The use of rocker sole shoe is one of the common interventions for increasing muscle strength in the elderly and young people. Despite the few studies on the effect of rockers in the elderly population, some have concluded that adding a rocker to the sole of the shoe can improve muscle strength in the long term and, thereby, improve postural stability. Achieving the desired effects on muscle strength requires rocker use on the sole for at least 6 months [20, 21, 22]. However, there is a concern that during this 6-month period, older people may have balance problems and slow walking. Thus, the present study aims to evaluate the short-term effect of toe rockers with specific angles on walking speed and postural control of the elderly.
Materials and Methods
This research is a quasi-experimental study with a pretest-posttest design. The inclusion criteria were being healthy and older than 60 years, while the exclusion criteria were having neuromuscular diseases, peripheral neuropathy, diabetes, acute musculoskeletal injuries, acute pain in the lower limbs and lower back, using walking aids, balance problems, and acute heart or lung diseases. To determine the sample size, first, a pilot study was performed on five older people. Assuming an effect size of 0.5, the minimum sample size was 19 to achieve a test power of 0.86. The participants’ dynamic postural stability was assessed by the Star Excursion Balance Test (SEBT). It is a reliable test with an intraclass correlation coefficient of 0.89-0.93 and a coefficient of variation of 0.3-4.6 [23]. To normalize the data, the SEBT results were divided by the leg length, and their mean values were used in the analysis [24]. The balance of participants was evaluated using the Persian version of the Berg Balance Scale (BBS), whose psychometric properties have been evaluated in a previous study [25]. The total score of BBS is 56, which shows the highest balance ability. The internal and external reliabilities of this test in the elderly are 0.98 and 0.99, respectively [26]. The walking speed was assessed using the 10-m walking test where the participant walks a distance of 20 m at a safe speed. The test was repeated 3 times, and the best record was set as the test score [27]. 
Ethyl vinyl acetate rubber was used to prepare the toe rocker in shoes with similar insoles and soles. The location of the rocker head was at 65% of the shoe length [28]. To maintain a safe environment for the elderly, the rocker angles were set at the maximum values, which did not increase the risk of falls in the elderly in previous studies [19, 29]. In the first test model, the rocker angle was 10 degrees (Figure 1), and in the second test model, it was 15 degrees (Figure 2).  The shoe’s sole was completely thick at the heel, at 65% of the shoe length. A shoe model similar to the test shoes, but different only in type and thickness of the sole, was used as the control shoe (Figure 3).  To analyze the data, first, the normality of their distribution was examined using the Shapiro-Wilk test, whose results showed a normal distribution for all data (P=0.2) except for the BBS data (P<0.001). Therefore, ANOVA and the Wilcoxon test were used to analyze the collected data.
Results
Out of 19 participants, 6(31.6%) were men, and 13(68.4%) were women. Their age ranges, mean of height, weight, Body Mass Index (BMI), and lower limb length ranges are presented in tables 1, 2, and 3. 






The Mean±SD BBS score in the control shoe group was 55.46±0.96, ranging from 52 to 56. This score was 55.21±0.98 in the shoe group with a 10-degree toe rocker and 55.26±1.05 in the shoe group with a 15-degree toe rocker; both ranged from 52 to 56. The result of the Wilcoxon test showed no statistically significant difference between the three groups regarding this variable (P=0.625). The Mean±SD score of the 10-m walking test in the control group was 1.14±0.24 m/s, ranging from 0.59 to 1.6 m/s. This score was 1.15±0.18 m/s in the shoe group with 10-degree toe rocker (range: 0.83 to 1.38 m/s) and 1.15(0.22) m/s in the shoe group with 15-degree toe rocker (range: 0.73 to 1.72 m/s). The result of the Wilcoxon test showed no statistically significant difference between the three groups regarding this variable (P=0.993). The result of the Wilcoxon test showed no statistically significant difference in SEBT score between the three groups (Table 4).


Discussion and Conclusion
The present study revealed that adding a toe rocker with angles of 10 or 15 degrees had no adverse effect on the balance and the walking speed of the elderly. The use of two rocker angles with certain values was based on previous studies, which showed that these rocker angles positively affected toe clearance during the swing phase in the elderly [19, 29]. Wearing rocker shoes reduces the person’s awareness of foot conditions by affecting the movement of the ankle joints and reducing the level of reliance [30]. Thus, due to compensatory mechanisms and caution, the travel distance in SEBT might be reduced after using rocker shoes compared to control shoes. However, the participants traveled relatively the same distance with all three shoe models. One of the reasons for the lack of significant differences in the results can be an increase in the person’s muscle activity to achieve a stable condition. Ghomian et al. [25], in a study on 17 patients with diabetic neuropathy, stated that when wearing rocker shoes, muscular strength increases in response to anterior and posterior stimuli to reach a stable condition. In other words, the lack of change in postural stability while wearing rocker shoes can be due to increased muscle activity and the person’s effort to maintain a stable posture. In their study, no significant difference was observed between shoes with toe rockers and control shoes regarding postural stability [31]. Brenton-Rule et al. evaluated the walking footwear on the postural stability of 21 healthy older adults. They also found no significant difference between the use of rocker shoes and regular walking shoes [32]. Ramstrand’s study of 31 women over the age of 50 showed that eight weeks of wearing MBT (Masai Barefoot Technology) shoes had no significant effect on the static stability of participants [21]. At the same time, the results of Albright et al. [44], Demura et al. [45], and Arazpour et al. [46] are contrary to our results. Albright et al. used shoes with rocker bottom soles, Demura et al. used shoes with rounded soft soles, and Arazpour et al. used shoes with heel-to-toe rocker soles. The discrepancy in results may also be due to the difference in the postural stability system between the elderly and young people. In all three studies, the participants were 20-25 years old, while the participants in our study were 66 years or older.
The results obtained from the 10-m walking test showed that the use of shoes with a 10- or 15-degree toe rocker did not cause a significant change in the walking speed of the elderly. Adding a rocker to the sole of the shoe increases the activity of ankle plantar flexors. If the rocker material is hard, it will prevent metatarsal joint movement, and, hence, the so-called metatarsal bone fracture will not occur. This status will increase the moment arm of plantar flexor muscles and eventually needs extra effort to lift the heel off the ground [36, 37]. On the other hand, the addition of a toe rocker increases the angle of hip extension in the middle and end of the static phase; as a result, the step length decreases [38]. At a certain distance, if the step length decreases and the cadence increases, the walking speed will not change. Forgani et al. and Arazpour et al. reported the same walking speed of the participants using control shoes and rocker shoes [35, 39]. Similar results were also observed in studies by Meyer et al. and Van Bogart [15, 38]. However, they suggested that the reason for the same speed when walking with rocker shoes was the increase of cadence and the decrease of stride length. One of the confounding variables and limitations of this study was the difference in the sole thickness in rocker-soled and control shoes. Although the effect of increasing the sole thickness on the weight of the shoes is statistically insignificant, the difference in the effect of the sole thickness on the balance is still debated. Since the results of clinical trials depend on the carefulness of the examiner and the location of the tests, all tests were performed in a place with standard conditions provided by an orthotist. It is recommended that other temporal and spatial parameters of walking in the elderly be evaluated in future studies by using rocker shoes.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information and were free to leave the study whenever they wished, and if desired, the research results would be available to them.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
Conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing – original draft preparation, writing – review & editing, visualization: All authors; Supervision: Mahmoud Bahramizadeh, Mokhtar Arazpour, Atefe Aboutorabi.

Conflict of interest
The authors declared no conflict of interest.
 

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