Correlation of back extensor strength with thoracic kyphosis and lumbar lordosis in estrogen-deficient women

Aging and osteoporosis have been associated with skeletal changes. Back extensor strengthening exercises are highly recommended for management of back pain, especially back pain related to osteoporosis. To our knowledge, the correlation of thoracic kyphosis, lumbar lordosis, and sacral inclination with back extensor strength, physical activity, and bone mineral density has not been critically studied in healthy, active, estrogen-deficient women. In a study of 65 such women (ages 48-65 yr), back extensor strength, bone mineral density, and physical activity score were evaluated and measured. These factors were then correlated with radiographic factors: (1) vertebral body ratios (anterior/posterior height) calculated for each vertebra from T-4 through L-5; (2) kyphosis index determined by adding the anterior heights of each vertebral body, T-4 through T-12, and then dividing the total by the corresponding sum of the posterior heights of each vertebral body; (3) thoracic kyphosis; (4) lumbar lordosis; and (5) sacral inclination. Back extensor strength had a significant negative correlation with thoracic kyphosis (r = -0.30, P = 0.019) and a positive correlation with lumbar lordosis (r = 0.26, P = 0.048) and sacral inclination (r = 0.34, P = 0.009). However, bone mineral density and physical activity score did not show any significant correlations with the radiographic factors. The results indicate that the stronger the back extensor, the smaller the thoracic kyphosis and the larger the lumbar lordosis and sacral inclination. We conclude that back extensor strength is an important determinant of posture in healthy women. However, prescribing back extensor strengthening exercises alone may also increase lumbar lordosis, which is not desirable.