I was having a discussion with a gentleman recently who was concerned about his bone mineral density results from two recent DXA scans. In addition to consulting with me about how to solve this, he also brought it to a group of HIT practitioners who, on the balance, are generally good-headed guys.
One of the gentleman in the group was concerned due to a piece in the New York Times about how exercise “doesn’t” increase bone mineral density (BMD). Let’s explore the studies presented.
- Aerobics-only (*Fart Noise*)
- Combined training, including 5 – 8 Rating of Perceived Exertion on a Borg scale for resistance training (*Wah-wah*)
- Resistance training or jump training (*The Price Is Right Fail Noise*)
So the last two studies cited actually showed an increase in bone as a result of resistance training, with concurrent improvement in functional measures like the sit-to-stand test or stair climb test. However, they did not increase their bone enough to reduce break risk as a result of a fall.
So what’s the problem? Well, the weights weren’t heavy enough. This isn’t some bro declaration, but rather a function of an untrained elderly trainee’s stunted efferent drive. This varies depending on the study, but a 2015 study showed that elderly untrained individuals were only able to generate ~2/3rds the force of a mass-matched young trainee. So training with 80% of their 1 rep max is really training with 50% of the muscle mass’s potential force production. This is a function of inactivity, not age, as a recent study showed that lifelong strength training resulted in similar efferent drive when compared to younger individuals.
As per Wolff’s law, we know that bones respond to loading, but given the above, they’re not seeing nearly the load required to stimulate sufficient bone regrowth. A recent study on a novel isometric loading device has shown that the bones of elderly individuals can safely tolerate 3 to 9 multiples of bodyweight (MOB) in the spine and hip, respectively. When the device was used as part of a 24 week study, not only did the osteoporotic trainees double the MOB their hip and spine were exposed to, but they increased their BMD by 16% in the hip and 15% in the spine as measured by DXA. These numbers are astonishing, as the studies above saw an increase in BMD of 1% over the course of the year.
To summarize: if you want bone, you need load. Heavy isometrics are a good start for someone who doesn’t have a novel device like the one in the studies above, or an ARX nearby. You can also progress it over time by adding weight week after week, as the participants of the study increased the force they generated (and thus the load their bones were exposed to) over the course the study.