1. Introduction
ower Crossed Syndrome (LCS) resulting in S-shaped posture of the lower back [1] is characterized by tightness and shortness of hip flexors and spinal muscles and weakness of the abdominal and serine muscles (Figure 1) [2]. This syndrome is also known as distal or pelvic crossed syndrome [1], which is caused by muscle imbalance [2]. Muscle imbalance is a condition where there is little balance between certain types of muscles. Some muscles are prone to shortening (tightening) and others are prone to lengthening (weakening) [6] which causes dysfunction of the joint, especially in the 4th and 5th lumbar vertebrae, 5th lumbar and first sacral vertebraes, sacroiliac joint, and hip joint [8]. Muscular imbalance in the lower limbs have a great impact not only on the biomechanics of the hip joints but also on the knee joint, ankle joint, shoulder joint, and other joints in the spine. Pathological worsening of lumbar lordosis causes worsening of cervical lordosis, increase of dorsal kyphosis, and misalignment of the sacrum [4], and by changing the distribution of biomechanical force in the lumbar region may lead to chronic low back pain [1]. Adopting incorrect postures due to lack of awareness and continuation of these incorrect habits in daily life can cause deviation of upright posture and create compensatory movement patterns [11]. Janda believed that in today’s society, muscle imbalance is exacerbated due to poor mobility, lack of movement, stress and fatigue [5].
There are several factors involved in the development of LCS that can be corrected by adopting a regular correction program [12]. The use of corrective exercises reduces postural abnormalities by improving and enhancing muscle balance and, consequently, improving the function of the motor system [12]. A corrective exercise program should be structured and purposefully designed, based on timing, for example; which is done by the manipulation of training variables over time to create more effective progress [7]. In General, these programs include stretching and strengthening exercises to correct the posture and reduce the pain caused by the posture correction [15]. Many studies have been conducted to find suitable methods to increase the level of physical fitness and correct the disorders that cause LCS. In this regard, different methods have been found [13]. Kaleh and Gijareh studied the prevalence of LCS in school children aged 15-13 years and found that these children have a pattern of muscle imbalance due to sitting for long hours during the day [8]. These postural abnormalities seem to be a simple muscle imbalance, but may put a lot of pressure on the country’s economy due to causing people to be unable to do daily tasks [14]. The later and longer the interval between the onset of postural abnormality and the start of treatment, the greater the vulnerability. In more severe cases, these abnormalities can lead to permanent disabilities. Therefore, identifying the mechanisms that affect the skeletal structure and correcting these compensatory abnormalities and preventing the aggravation of these abnormalities and the subsequent possible damages are very important. Correction of postural abnormalities at a young age avoids spending huge costs for surgery and treatment in the future [12]. Due to the lack of research on the timing of stretching and strengthening exercises and its effect on LCS and considering the importance of this issue in everyday life, the question that arises is: which of the intermittent and simultaneous exercises can have a greater impact on improvement of LCS. In this regard, this study aims to compare the effect of eight-week of training program using two different stretching and strengthening exercises (intermittent and simultaneous) on the status of LCS in female college students.
2. Methods
In this quasi-experimental study, study population consist of 300 female students of Guilan University aged 19-25 years. They were evaluated for lumbar lordosis using the New York Posture Rating tool. Of these, 120 with hyperlordosis were re-evaluated by a flexible ruler to accurately measure the lumbar arch. Finally, 45 students with a curvature angle of more than 45 degrees were selected as samples with LCS and were randomly divided into three groups of intermittent training (n=15), simultaneous training (n=15), and control (n=15). The training program consisted of corrective exercises for 8 weeks, 3 sessions per week, each for 60 minutes. One-way analysis of variance was used to analyze the data in SPSS v.20 software.
3. Results
The difference between the intermittent training and control groups was significant (p=0.30), while no significant difference was observed between the simultaneous training and control groups (p=0.68).
4. Discussion and Conclusion
Performing stretching and strengthening exercises intermittently has a greater effect on reducing LCS than performing these exercises simultaneously.

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. They 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 specific grant fromfunding agencies in the public, commercial, or not profit sectors.

Authors' contributions
Conceptualization, methodology, supervision: Both authors; Preparing the manuscript, resources: Chiman Alyarnezhad; Review-editing: Ali Shams Majalan.

Conflicts of interest
The authors declared no confict of interest.


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