Strength Training for Bone Health

Osteoporosis is a problem in today's society, affecting millions of people every year. While low bone density can affect both genders it is more prevalent amongst females and often starts during the teenage years. Bone density is most effectively increased before the age of 30 after this age a natural decline in bone density makes it difficult to see a net accumulation of bone mineral. Addressing the issue of bone density during the teenage years can help prevent future complications that may arise from osteoporosis.

Strain and Bone formation

We have known for more than a century that there is a relationship between mechanical loading and bone hypertrophy. Certain types and volumes of physical activity increase bone mineral density (BMD) while immobilization or bed rest decrease bone density. When a force is applied to a material such as bone there is a certain amount of bending or deformation. The amount of bending compared to its original length is known as strain. When muscles pull on bones with sufficient force strain is created where the muscle attaches to the bone. Strain and rate of strain are the two most important factors responsible for increased bone density through exercise. Strength training, when done at a high enough intensity, can provide sufficient strain to increase bone density but it is not the most effective means of increasing bone density; jumping, because it creates a higher strain and rate of strain, has been shown to be the most effective form of exercise for increasing bone density. A recent study of adolescent girls found that adding 10 maximal effort jumps to a PE class 2-3 times per week is sufficient to increase bone density in the legs, hips and spine. While jumping is the fastest way to increase bone density weight training has the advantage of incorporating the whole body. Bone density increases are very specific to the muscle groups and body parts used in the exercises. For example squats will increase bone density of the head of the femur and lumbar spine but do little for bone density in the wrists, cervical, or thoracic spine while bench pressing increases bone density of the wrists and clavicles but not in the lower body.

Many popular magazines and other publications promote weight bearing exercise such as walking or jogging for improving bone density. While this is an acceptable prescription for older adults who have been sedentary for long periods of time it is insufficient to improve BMD in younger people. In fact, volumes of aerobic training in excess of eight hours per week can result in decreased bone density. This is one of the reasons for keeping strength training in the programs of endurance athletes all year round.

Strength Program design for increased bone density

A well balanced program begun during adolescence can reduce or eliminate the effects of osteoperosis. Consider these guidelines for designing programs to improve bone density.

Use a progressive program

Increase resistance progressively. This is necessary because for bone to form it requires a minimum amount of strain. Once a bone adapts to a given strain level, the stimulus for bone to form is removed and a higher strain level becomes necessary for it to adapt further. Increase the resistance used at regular intervals, every 2-3 weeks to ensure continued progress.

Speed of movement

While it is common for strength training exercises to be done in a slow controlled fashion this is not the best approach to increasing bone density. Higher speed movements and the attempt to move at a high speed create higher rates of strain and improves the effectiveness of strength training for increased BMD. The addition of Olympic style lifts to the program is an excellent way of increase the rate of strain. Olympic style lifters have been shown to have some of the highest levels of bone density in athletes.

Vary the exercises

Increases in BMD during strength training are related to the load placed on the muscles around the bone. Evidence supporting this hypothesis comes from the lack of adaptation in total body BMD and lack of increased BMD in bones surrounded by muscles that do no act as prime movers. Changing the distribution of strain is important to develop new bone and may be more critical than the amount of strain. Changing exercises frequently, and subsequently the muscles used, will help change the distribution of strain and ensure that a wide variety of muscles act as prime movers.

Minimum intensity

There is a threshold below which the resistance and strain placed on the bone are insufficient to increase bone density. Current research suggests that this around 70% of 1RM and that exercise below this intensity will have limited effects on bone density.

Duration of program

The bone remodeling cycle lasts four to six months. This is the minimum period of time needed for BMD to change significantly. Training must be done at least three times a week for a year to see measurable increases in bone density. Ideally strength training becomes part of an active lifestyle that will help maintain bone mass through adolescents into adult hood and old age.

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