Bones density – it’s a concern for women over the age of 50 – osteoporosis isn’t just a problem for older women, gymnasts, ballerinas, and some female athletes are at high risk due to a reduction in estrogen from being underweight and over-exercising.
Women who do long periods of endurance exercise and don’t consume enough calories are at particularly high risk for bone loss, even at a young age. It’s not uncommon for young women who over-train and are underweight to experience exercise-related amenorrhea where their estrogen levels drop and their periods stop. So, osteoporosis can strike well before menopause.
One thing ballerinas and endurance athletes have in common is they don’t focus on developing strong muscles. Instead, they’re more likely to eat a low-calorie diet to keep their weight down and not strength train. But what about women who DO focus on strength training? Is there a link between strong muscles and strong bones?
Bone Mass and Strength Training
In studies comparing men and women who do endurance exercise, like long-distance running, with those who do strength and power training, the power and strength guys and gals have greater bone mass, on average. Other research shows postmenopausal women without osteoporosis have more dynamic strength, on average, relative to women with the disease.
Yet another study showed a link between bone density and the quantity of weights participants lifted during a year-long strength-training program. Those who lifted more frequently had higher bone density. In fact, some experts wonder whether dynamic strength testing might be a useful screening tool for osteoporosis.
These results aren’t surprising. Almost any health care professional will tell you high-impact exercise is a stimulus for bone growth – but so is high-intensity resistance training. At the same time, light dumbbells and high reps do little to increase bone mass or the size of your muscles. The real benefits come from heavy resistance training.
How does strength training build bone mass? Each time you contract a muscle, the muscle pulls on a tendon, and the tendon pulls on a bone. Here’s the catch. For muscle contractions to lead to a meaningful increase in bone mass, the stimulus has to be strong enough to stimulate the formation of new bone. In fact, there’s a certain threshold stimulus you have to apply to a bone to get it to lay down new bony tissue. This threshold is called the MES, or minimal essential strain.
How high is the minimal essential strain? It’s roughly a tenth of the force that would fracture the bone. This corresponds to using a resistance of between 80 to 90% of your one-rep max, a resistance considered optimal for building strength.
How New Bones are Formed
When you contract a muscle with enough force, at least the minimal essential strain, bone cells called osteoblasts go to work making and laying down new bone. As mentioned, high-impact exercise, like plyometrics, running, jumping rope, and step training, does the same thing. Low-impact activities, like cycling, don’t provide a sufficient stimulus for bone growth.
Other cells called osteoclasts are responsible for breaking bone down for remodeling. Bone is a dynamic tissue that’s constantly being “reinvented.” For healthy bones, you want osteoblast activity to be stronger than osteoclast activity. In fact, a study of 32 competitive male cyclists showed they had lower bone density than a group of non-cycling controls. Of course, cyclists don’t do a lot of strength training. It would be interesting to measure the bone density of cyclists who also lifted heavy weights.
Are Some Strength Exercises Better for Stimulating Bone Growth?
Exercise that works the hips and back are ideal since the force is transmitted not only to the bones in the hip (Who wants a hip fracture?) but to the spine as well. Compound exercises that work multiple muscle groups and joints are best for building bone. Examples are squats, lunges, and deadlifts. Isolation exercises aren’t as effective as compound exercises, but they may help prevent fractures of smaller bones like your arms and wrists.
With strength training, don’t expect quick improvements in bone health. Increasing bone density happens a little at a time, over many years. Still, even small improvements can make your bones more resistant to fractures. The key is to be consistent with strength training. When you strength train, you’re increasing muscle strength and promoting bone health at the same time.
If you already have osteoporosis or have had a fracture related to osteoporosis, talk to your doctor before doing exercises that involve bending over or twisting your trunk.
Don’t forget – you’re at higher risk for osteoporosis if you’re post-menopausal, thin, have a small bone structure, smoke, or have a family history of osteoporosis. If you fall into one of these categories, your doctor may recommend getting a bone density study, usually, a DEXA scan, earlier so they can closely monitor you for bone loss. A DEXA scan will reveal whether your bone density falls into the osteopenia or osteoporosis category. If you have osteopenia, it doesn’t mean you have osteoporosis – it means your bone density is lower than normal but not low enough to be classified as osteoporosis.
The Bottom Line
Strong muscles are correlated with strong bones. In general, women who do high-resistance strength training have stronger muscles and greater bone mass. Still, lifting weights is no guarantee you won’t develop osteoporosis. That’s why monitoring is so important. Make sure you get a bone density study at the time your doctor recommends. Whatever you do, keep strength training.
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Journal of Strength & Conditioning Research. October 2013 – Volume 27 – Issue 10 – p 2879-2886.
National Osteoporosis Foundation. “Low Bone Density”
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