1. Introduction
Blindness is one of the problems faced by the World Health Organization. The visual system provides information about the position and movement of the head relative to objects around the body. This sense can report how the head moves and information about the direction of the body [4]. Visual impairment reduces balance and causes disorders, falls, job disability, and recurrent injuries [5, 6]. Sensory input information is provided through the vestibular or somatosensory system [7, 8]. Therefore, blind people need much more information about the vestibular or somatosensory system due to visual impairments. On the other hand, low mobility, movement limitations [9], and fear of movement in these people make it challenging to receive and transmit information from sensory-deep receptors to the CNS. Therefore, appropriate treatment methods or sports activities should be used to restore the activity of sensory-deep receptors in these people.
Foot massage is one of the treatment methods that can have a positive and significant effect on the activity of the foot receptors. Various studies on different samples have shown that massage and stimulation of the foot receptors can positively and significantly affect the sense of depth perception and postural control. Foot massage and stimulation of the foot receptors improve postural control in people with ankle sprains [26]. It has also been shown foot massage improves balance and postural control in people with type 2 diabetes and the elderly [27-29].
2. Materials and Methods
This study was quasi-experimental with a pretest-posttest design with three training intervention groups. The statistical sample consisted of 30 eligible blind people in Sanandaj City between 20-30 years of age, selected by purposive sampling. According to previous research, the minimum sample size was considered for each group of 10 people in this study. Samples were determined using the equation of estimating the G-Power sample size and considering the test power of 80% [26].
To determine the samples, they first referred to the Sanandaj City Association of the Blindness, and then, by studying their files, they registered people who were completely blind (congenital). Then, the people who voluntarily intended to participate in the research were selected by presenting and explaining the research process to them. Inclusion criteria were as follows: boys in the age range of 20 to 30 years, complete congenital blindness, no fracture or lower limb surgery, no knee injury, lack of deafness and atrial system disorder, lack of surgery on the joints of the lower limbs, and no history of neurological disease or medication use that affects the nervous system.
Exclusion criteria included the occurrence of any pain during the massage procedures, hypersensitivity of the soles of the feet while performing foot massage procedures, lack of cooperation, and withdrawal from participation during the study [30-33]. In this study, three different massage methods were performed on the soles of the feet of the blinds, and a Biodex balance system was used to measure balance.

3. Results
This study was quasi-experimental with a pretest-posttest design with three training intervention groups. The statistical sample included 30 blind people in Sanandaj City. The ANOVA test results showed no significant difference between the three groups in terms of height, weight, and age (P>0.05), and the three groups are considered homogeneous in all cases. Also, the results of the Shapiro-Wilk test showed the distribution of all measured data was normal.
The results of one-way analysis of variance (ANOVA) test in the posttest stage showed between groups in the general static equilibrium index of P=0.402, F=0.56, in the anterior-posterior index of static surface P=0.481, F=0.752, and in the internal-external index of static level, P=0.429, F=0.782, there is no significant difference between blind people. All three massage techniques have the same effect on the samples.
The one-way analysis of variance in the posttest showed a significant difference between the groups in the general dynamic equilibrium index (f=31.25, P=0.001) and the internal-external index of dynamic level (f=16.01, P=0.001). Hand massage has improved more than the other two massages in the above two indicators. There was no significant difference between the other two massages (brush massage with ball massage). Differences between groups in durability related to massage methods in static and dynamic balance indices were also insignificant.
4. Conclusion
This study aimed to compare the effect and durability of foot massage methods on the balance of the blind. The results generally showed the foot massage techniques improved static and dynamic balance. Also, there is no significant difference between the effect of foot massage methods in most variables. These three types of massage have almost the same effect on the research variables. And only in hand massage compared to the other two massages, a significant difference was found on the overall dynamic balance index (P=0.001).
The application of stimuli such as massage from the external environment to the body can enhance the activity of neurons to transmit nerve messages. Like other physical fitness factors, in the present study, the activity of sensory-deep receptors is also affected by the amount of physical activity and participation in sports activities. Therefore, this factor can also be considered involved in the low activity of receptors in these people.
This study shows that foot massage techniques have improved static and dynamic balance, which results in improved sensory receptor activity. Sensory-deep receptors in the legs have several nerve endings that communicate with different systems and organs within the body. Massage and stimulation of skin receptors can restore receptor activity and ultimately improve the sense of depth [26].
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
All authors equally contributed to preparing this article.
Conflicts of interest
The authors declared no conflict of interest.

 

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