Preventing Osteoporosis: The Effect of High Intensity Strength Training on Bone Mineral Density in Young and Healthy Women

Background:

Osteoporosis is a progressive, systemic skeletal disorder characterized by low bone mineral density (BMD), and deterioration of the microarchitecture of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. Typically the disease shows no symptoms until a fracture occurs, hence referred to as the "silent epidemic". In Norway one of two women and one of four men experience a fragility fracture after the age of 50. The loss of bone strength with age likely reflects the skeletal response to hormonal changes and the mechanical environment with decreased physical activity. Osteoporotic fractures often happen as a consequence of minimal injury, especially at the hip, spine and wrist. Hip fracture is associated with excess mortality during the first year after fracture ranging from 8.4% to 36%. The increased mortality risk may persist for several years thereafter, highlighting the need for interventions to reduce this risk. Osteoporosis is a common disease and recognized as a global problem by the WHO.

The American College of Sport Medicine suggests exercise as a countermeasure against bone loss in postmenopausal woman and elderly subjects. Peak bone mass is thought to be attained by the end of the third decade, hence the early adult years might be the final opportunity for its augmentation. It is indicated that optimizing peak bone mass may have long-term effect on bone health. Intervention studies with young women show that high impact exercises may improve BMD in young adults. High intensity strength training also seems to effectively improve BMD and the ratio of bone turnover markers. Furthermore, an explosive execution of movement may be important for obtaining BMD improvements from resistance training. Maximal strength training (MST) is characterized by high mobilization of force, high loads, and few repetitions (3-5 reps.) per set with emphasis on maximal force mobilization in the concentric part of the movement. Recent studies have shown that MST is highly efficient for improving maximal strength (1RM) and rate of force development (RFD). Parameters such as 1RM and RFD are closely related to BMD. In addition, a recent study from our group showed that 12 weeks of MST training (three times each week) improved bone mass in the hip and spine of postmenopausal women, diagnosed with osteoporosis (article in preparation). In the present study we want to investigate the impact of heavy, explosive strength training on bone mass and bone metabolism in young and healthy woman which have not yet reached peak bone mass.

Physical activity and BMD:

One of the main factors responsible for the high incidence of osteoporosis is physical inactivity. Several studies have shown that physical activity can lead to an increase in BMD. Resistance- and impact exercises have shown to be most effective. A number of studies performed with sedentary young women performing high impact training has shown significant improvement in BMD at the femoral neck and lumbar spine. A study with postmenopausal women showed that power training is more effective in maintaining BMD in the lumbar spine and total hip than conventional strength training.