Investigating the effect of whole body vibration with different frequency and amplitude on bending strength, calcium ion density and histomorphometry of femur and tibia in urectomy rats.

Dissertation for receiving a doctorate degree in the field of physical education, sports biomechanics

Abstract:

Osteoporosis is a skeletal disorder in which the mechanical strength of the bone is reduced and leads to bone fracture, so paying attention to methods to maintain bone strength and prevent osteoporosis is considered important.  The aim of this research was to determine the effect of whole body vibration with different frequency and amplitude on mechanical resistance, calcium ion concentration and histomorphometry of femur and tibia in orectomy rats. After three months, 41 oractomy rats were randomly divided into 5 groups: high-frequency, high-amplitude group (n=9), high-frequency, low-amplitude group (n=9), low-frequency, high-amplitude group (n=9), high-frequency, high-amplitude group (n=9), and Sham group (n=5). 6 healthy rats without oractomy surgery were also included in the control group. The training groups were 3 times a week for 8 weeks. The appliance was on the extinguisher of the same protocol. Absorbing Flame spectroscopy (spectrophotometry) was evaluated. The left femur was prepared and stained with hematoxylin and eosin for histomorphometry. The results showed that eight weeks of vibration exercises had a significant effect on the bone's mechanical resistance and brought the bone's biomechanical parameters to the level of the healthy bone. Among the training groups, the HFLA group showed a greater increase in bone mechanical resistance than the other training groups, and the bone mechanical resistance in the HFLA and LFHA training groups, both of which had almost the same training intensity, but the results of the biomechanical parameters in the HFLA training group were significantly better than the LFHA group. In rats after orectomy, the tibia responded better to WBV exercises. WBV training on calcium ion concentration increased in all training groups and reached the normal level in the control group (healthy) and in the sham group it was lower than the rest of the groups, although the difference was not significant.  In both dense and spongy bones, the high frequency group, the low amplitude (HFLA) had the largest increase in area compared to other training groups. There is a correlation between bone mechanical resistance indices and bone histomorphometric indices.

Key words: whole body vibration, bending strength, calcium ion density, histomorphometry, rat orectomy

1- Introduction

Osteoporosis is a serious problem for It is the health of the society as a whole that affects the quality of life of society people, especially middle-aged women. Osteoporosis is a skeletal disorder in which the mechanical strength of bone decreases and leads to bone fracture. The reason for the importance of this disease for the country's health system is the fractures and, as a result, the imposition of material and spiritual costs resulting from this condition. Considering the importance of osteoporosis disease and the pivotal role of prevention of this disease, it is obvious that attention and sensitivity towards this disease at all levels of providing healthcare services in the country as well as the general society, especially women and girls in the country, is very necessary and important. Several studies have shown the role of physical activity in the prevention and treatment of osteoporosis. Recently, whole body vibration [1] (WBV) as a sports intervention is a promising solution in the field of exercise and rehabilitation, to increase strength and power, a lot of attention is devoted and used. It has been observed that vibration is effective in improving bone strength in orectomized rats and humans. Despite the numerous researches reported on the benefits of vibration in maintaining bone density in animals, not all researches confirm this issue.. Also, the question of which vibration protocol including a specific frequency and amplitude has an optimal effect on bone resistance has not yet had a clear answer. The purpose of this research is to investigate the effect of four different types of vibration signals on the strength of the bone tissue of orectomy rats in order to investigate the importance of the change of the vibration signal on the mechanical behavior of the bone that will be caused by the ossification phenomenon. Global [3] (WHO, "is a skeletal disorder in which the mechanical strength of bones is reduced and leads to bone fractures". The World Health Organization has defined osteoporosis as a decrease in bone density to 2.5 standard deviations below the average maximum bone density in young people in the community (1). Men who are overweight naturally lose about half a percent of their bone mass per year upon entering adulthood. Women experience rapid mass loss when they enter menopause. Bone loss is up to 5% per year for spongy bones and between 3% and 2% per year for dense bone. Therefore, bone density decreases by 20% to 30% over the course of 20 years. In addition to imposing an economic burden on the individual and society, these fractures also result in social costs such as disability or death (3).

To investigate bone growth in humans, studies are mainly limited to radiography or the evaluation of bone markers, while the use of animal models directly investigates the mechanical properties of bone. The mechanical properties of bone, including: stress, bone stiffness and the amount of absorbed energy are the main parameters that express bone structure and function. Therefore, by using animal models and performing direct biomechanical tests, a better reflection of the mechanical properties of bone is obtained compared to bone density measurements (4).  

It has been determined that rat orectomy is a suitable experimental model for investigating osteoporosis in the menopause, which can be seen a few months after orectomy (5). The proximal region of the rat bone is also very similar to the human femur. Due to the great similarity between human and rat bone, it is used to evaluate bone strength and morphological changes (6).   According to medical findings, the bone tissue undergoes regular renewal. The general process of this process begins with bone resorption by the stimulation of osteoclast cells. Bone formation is done by osteoblast cells. If bone absorption is high or bone formation is reduced, osteoporosis occurs, and the main mechanism of all the causes of osteoporosis is this imbalance between bone absorption and its formation (7).

Among the stimulating and anti-analytical factors of bone, sensitivity to the mechanical environment is actually the Wolff's law that determines the shape of the bone and its functional nature. The relationship between the bone structure and the forces acting on it is from the ability of healthy bone to adapt to the environment under load, and on this basis, it allows the skeletal system to adapt to the existing environment. This ability is generally due to the properties of bone regeneration [4] and reconstruction [5], which destroys the old bone tissue in the environment of minimum or maximum bone loading and causes its re-formation in the environment with appropriate loading. This adaptability of the skeletal system to the environment creates significant changes in the mass, geometry and properties of bone materials (8, 9). On the other hand, any type of movement and activity on the ground also mechanically causes load [6] on the weight-bearing bones and improves their structure. Bone formation and resorption is sensitive to external force caused by gravitational force and internal force produced by muscle activity (10). Applying load on bone is known as the necessary stimuli to achieve peak bone mass and maintain its homeostasis (11).