Introduction and purpose:
The spine is one of the most remarkable parts of the human body that bears changes due to the amount of mechanical pressure applied over time. The thoracic spine area is one of the most important parts of the spine that can be the source of disorders and pain throughout people's lives.
Kyphosis or abnormal increase in the arch of the thoracic area is one of the most common postural abnormalities and also is one of the most significant causes affecting the pathology of the upper quarter of the body which involves most of the soft tissues and is often observed during adolescence and youth.
The purpose of this research is to assess the amount of kyphosis and provide the norm of kyphosis for 807 female students (aged 12 to 18 years) in Mashhad City by using a kyphometer.
Material and Methods
The research that is based on the nature and method of data collection is cross-sectional and practical in terms of purpose. First, the demographic information of people including their age, weight, height, and body mass index was recorded. To assess and determine the kyphosis angle, the participants were placed in a natural and comfortable standing position, so that the legs were next to each other and at a little distance from each other, and the body weight was equally distributed on the legs. In this case, the shock appendage of the second and twelfth back vertebrae of the subject was marked and by placing the kyphometer on each of the considered vertebrae, the kyphosis angle of the subjects was determined and recorded. To decrease the percentage of error in the measurement the kyphosis angle was evaluated and recorded two times.

Findings
After completing the data collection and statistical analysis process, the mean, standard deviation, and range of the norm were obtained as 23.68, 6.36, (9.50-44.50) respectively.
Conclusion and Discussion
According to the results of this research, meantime presenting the norm of the kyphosis angle of girls aged 12-18 years in Mashhad city, it can be stated that this group of students who were evaluated has a better condition than other age groups in terms of the evaluated index.