Relationships Among Body Mass Index, Body Balance and Bone Mineral Density

• The purpose of the current study was to evaluate the relationships among body mass index (BMI), body balance, and BMD (g/cm²) in postmenopausal women to be able to identify risk factors for fractures.
• Forty-eight postmenopausal women participated in this study. Body balance was assessed using Berg Balance Scale (BBS), while BMD of the lumbar spine was measured by dual energy X-ray absorptiometry (DEXA) scan.

The positive correlation between body balance and BMD in the current study can be explained that balance is controlled by sensory input, central processing, and neuromuscular responses. The sensory components consist of the vestibular, visual, and proprioceptive systems. An effective motor response requires an intact neuromuscular system and sufficient muscle strength to return the COG within the BOS when balance is disturbed. Postural balance in individuals with osteoporosis is significantly worse than in healthy individuals. Moreover, it was determined that balance scores in individuals with osteoporosis were 11% worse than scores of healthy individuals. Furthermore, exaggerated thoracic kyphotic curve is not only a disfiguring effect of osteoporosis but may also play a significant role in gait disorder, instability, and risk of falls.

In addition, back pain has a harmful impact on both balance and functional mobility in women with osteoporosis. Individuals with back pain may reduce their level of physical activity and, as a result, become weak in muscles required for balance and functional mobility. Impairment of the musculoskeletal and/or the neuromuscular system may negatively affect both balance and functional mobility.

In the same context, it was proved that women with decreased BMD and increased thoracic kyphosis presented greater body sway in the anterior/posterior direction on the force platform indicating more displacement of foot center of pressure (COP). They also confirmed that postmenopausal women with low BMD and increased thoracic kyphosis depend more on the hip strategy to maintain their postural control. This in turn probably causes more displacement of foot COP, thus causing greater body sway in all directions in comparison with the ankle strategy. it was also showed that women with loss of bone mass and increased thoracic kyphosis presented less foot COP displacement in the AP direction compared with the control group (with normal bone mass and normal thoracic curve.

The current study results also revealed that BMI was negatively correlated with both BMD and body balance in postmenopausal women. This can be illustrated that obese elderly women are often afraid of falls and sustaining fractures, so they prefer immobility and minimize their physical activity as much as possible. Because bone is formed when needed and resorbed when not needed as known as Wolff's law, BMD decreases and osteopenia/osteoporosis develops. Low BMD affect bone health as it leads to fragile weak bone and this in turn disturbs postural control and body balance. Additionally, obese women fail to control their center of gravity (COG) within base of support (BOS) disturbing their postural control and body balance, increasing risk of falls and making them more liable to fractures.