Doctors know that weight-bearing exercise helps build bone mass in women after menopause. Research has shown that strength training can be especially helpful. But nobody knows exactly how it works. If they did, doctors could better design individualized programs to help prevent or treat osteoporosis.
These authors tested whether lifting larger amounts of weight led to higher bone mass. They assigned 140 postmenopausal women to three sessions of strength training a week for one year. The one-hour sessions included two sets of six to eight repetitions of eight different weight lifting exercises. The exercises were meant to strengthen the arms, legs, and body. Some were free weight exercises, and some used machines. The women lifted 70 to 80 percent of their maximum in each exercise. All the women took calcium, and half of them were on hormone replacement therapy.
Their bone mineral density (BMD) was measured at the beginning of the strength training and again one year later. The BMD was measured in three different spots: the femur trochanter (the large bump at the top of the thigh bone), the femur neck (the skinny part of the thigh bone by the hip joint), and the lower spine. The authors found a definite relationship between lifting more weight and increasing the BMD in the femur trochanter. The authors note that this strength training program put the most direct weight load on the femur trochanter. Comparing the different exercises, they found that weighted squats seemed to have the biggest impact on BMD growth.
These results are interesting for many reasons. They suggest that intense strength training programs seem to build more BMD than easy programs. They also open up new questions about the complex ways that bones and muscles interact. The authors also note that many questions remain about how hormone replacement therapy combines with strength training in building BMD. The authors feel that this study will be a good foundation for future research on helping postmenopausal women build stronger bones.