Comparison of Changes in Center of Pressure and Time to Stabilization in Students With and Without Hyperlordosis

* Corresponding Author: Mohamadreza Hatefi Address: Department of Biomechanics and Sport Injuries, Faculty of Physical Education and Sports Sciences, Kharazmi University, Tehran, Iran. Tel: +98 (912) 2440394 E-Mail: hatefimohamadreza@yahoo.com 1. Department of Sports Pathology & Corrective Exercises, Faculty of Physical Education and Sports Sciences, Allameh Tabataba’i University, Tehran, Iran. 2. Department of Biomechanics and Sport Injuries, Faculty of Physical Education and Sports Sciences, Kharazmi University, Tehran, Iran. Farideh Babakhani1 , *Mohamadreza Hatefi2 , Mona Heydarain1 , Masod Barzegar1


Introduction
ne of the most common abnormalities in high school students is lumbar hyperlordosis [2]. Hyperlordosis is spinal deformity occurring on the sagittal plane; excessive lumbar curvature causes the forward dis-O placement of the center of gravity and increases pelvic motion [3]. As a result of increased lumbar lordosis, the erector spinal muscles and hip flexors become shortened or stiff. Besides, the abdominal muscles and hip extensors become weak or stretched. Natural lordosis in the lumbar region protects it against excessive pressure and acts as a shock absorber [4,5]. Murray et al. compared balance between individuals with and without ankylosing spondylitis, a form of fixed kyphosis; they concluded that these patients have more postural fluctuations, compared to healthy controls [15]. However, Aydog et al. reported no significant difference in postural fluctuations and the Center of Pressure (COP) between the two groups [16]. Spinal deformities may displace the center of gravity and affect balance. Thus, investigating the effect of spinal deformities can provide beneficial data on the balance function of these individuals. Such information could be applied to adopt effective methods to reduce the effects of these abnormalities on their ability to maintain balance, health promotion, and sports performance. Various methods are available to evaluate dynamic balance. Numerous researchers have used the Star Excursion Balance Test [18]; however, it is not as functional and dynamic as the jump-landing task required to measure Time to Stabilization (TTS) [19]. TTS assessment is the latest instrument for neuromuscular control measurement. TTS uses sensory and mechanical systems to perform complex jump-landing task. As a result, it indicates the body's ability to minimize postural fluctuations when transferring from a dynamic position to a static state [20]. It is also very sensitive to postural stability disorders [21]. This study aimed to compare the changes in COP and TTS between students with and without hyperlordosis.

Participants and Methods
In total, 30 female high school students in Tehran Province, Iran, aged 14-15 years, participated in this study. They were selected by a convenience sampling technique and based on the study inclusion criteria. They were divided into two groups of patients (n=15) and controls (n=15). The subjects' lumbar spine curvature was evaluated by a 30-cm Iranian-made flexible ruler like the French curve; its' reliability and validity have been reported as 98% and 82%, respectively, in Iran. COP parameters to examine the balance in double-leg standing position with eyes open and closed included the following: the range of variation (R), Path Length (PL), Standard Deviation (SD), and Root Mean Square (RMS) in Anterior-Posterior (AP) and Mediolateral (ML) directions; average radial displacement (RDavg), standard deviation of RDavg, Total Path Length (TPL), as well as the ellipse surface area of base of support (CEA). The assessments of changes in COP were performed in 30 seconds with eyes open and closed. Foot COP information was recorded in lateral and anterior-posterior directions by force plate [22,24].
To measure TTS in three directions of vertical, AP, and ML, the study participant was requested to stand on a  [25]; then, land on the center of the force plate with one foot (the dominant foot). Accordingly, as soon as positioned, the si=subject must have placed the hands on the pelvic area, hold the head up, and look forward while trying to maintain balance. Before that, the study subjects were requested to hit the ball to determine their dominant foot [26,27].

Results
There was no significant difference between the two groups in any variables of COP when standing with eyes open (Table 1) and closed. In some cases, the variables were slightly different; however, this difference was not statistically significant (P>0.05). Regarding TTL, there was a significant difference between the study groups in three directions of vertical, AP, and ML. In those with hyperlordosis, the TTL was longer than that of the controls (P<0.05).

Discussion
The present study results suggested no significant difference in foot COP variables in standing with eyes closed and open between two groups of healthy and hyperlordosis individuals. However, the TTS result was significantly different between the two study groups. Physical posture is always in a state of fluctuation, and its balance is maintained by the combined reactions of visual, proprioceptive, and vestibular senses data [28]. Based on the literature, COP displacement has been used as an indirect attribute of postural fluctuation and one's ability to maintain balance and postural control, consequently [29].

Conclusion
Abnormal spine alignment (hyperlordosis), as a risk factor, can affect dynamic balance index (i.e. TTS); however, it has no effect on the static balance index (i.e. COP) with eyes open and closed. Therefore, the improvement of hyperlordosis deformity may improve postural control in dynamic balance indices.

Compliance with ethical guidelines
All ethical principles were 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; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research would be available to them.

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

Authors' contributions
All authors contributed equally in preparing all parts of the research.

Conflicts of interest
The authors declared no conflict of interest.