Lab Notes · 6 min read
This one is about bone. Your bone is living tissue. It is taken apart and rebuilt continuously for your entire life, and the thing that decides whether it comes back heavier or lighter is mechanical load.
Inside your skeleton are cells that lay bone down and cells that take it away. They take their instruction from how far the bone bends when you load it. That bending is called strain, and the size of the strain is the whole signal.
The loading experiments that established this found a threshold. Below a certain strain, bone is removed and the outer shell gets more porous. Above it, new bone is built on the inner and outer surfaces. The size of the force is what moved the needle, not how many times it was applied.
Rubin & Lanyon, Calcified Tissue International 1985;37(4):411–417 · strain below 0.001 produced bone loss, above 0.001 produced new bone formation
Estrogen restrains the cells that take bone away. As estrogen falls through the menopause transition, that restraint comes off, and removal runs ahead of building.
The timing is known in detail, because thousands of women were measured all the way through it. Fast bone loss starts about a year before the final period and runs for roughly three years after it. The spine goes faster than the hip. Across that decade a woman loses about a tenth of her spine.
Greendale et al., Journal of Bone and Mineral Research 2012;27(1):111–118 · SWAN multiethnic cohort; rapid loss averages about 2% a year at the spine, roughly 10% over the decade
Every woman goes through this. What changes from one woman to the next is what she is doing while it happens.
Walking has been measured against bone density directly, and more than once. Pooled across the controlled trials, walking produced no significant change at the spine in postmenopausal women. A second pooled analysis found the same result at the spine and at the whole body.
Martyn-St James & Carroll, Bone 2008;43(3):521–531 (8 trials) · Ma, Wu & He, Menopause 2013;20(11):1216–1226 (10 trials)
The reason is in the first section. Your skeleton already carries your body weight every day of its life. Walking asks it for a force it is long since used to, so the strain stays under the cut point and the building cells are never called.
A weight you can lift twenty times produces a force your bone already meets. Adding repetitions to that set raises how tired you get at the end of it. Bone reads the peak force in the set, so a longer set of a light weight arrives at the skeleton as more of the same.
That is not a judgment on anyone who has been doing it. It is the most common recommendation given to women with thinning bone, and the research has now compared it head to head with something heavier.
In the LIFTMOR trial, postmenopausal women with low bone mass trained twice a week for eight months. Thirty minutes a session. Heavy sets of five repetitions, deadlift, overhead press and back squat. Their spine bone density went up, and their femoral neck went up with it.
The comparison group did a low-intensity home exercise program for the same eight months and lost bone at both sites.
Watson et al., Journal of Bone and Mineral Research 2018;33(2):211–220 · LIFTMOR randomized controlled trial, 101 postmenopausal women with osteopenia or osteoporosis; 5 sets of 5 above 85% of one-repetition maximum; lumbar spine +2.9% vs −1.2% in controls, femoral neck +0.3% vs −1.9%
Same women, same age, same eight months. The difference between the two groups was how much weight was on the bar.
If you have been diagnosed with osteoporosis, if you have broken a bone, or if you are under a doctor’s care for anything, be cleared by your own doctor before you begin. We are certified exercise specialists. We do not diagnose and we do not treat, and we train inside whatever your physician tells you.
Most women arrive at a gym wanting fat loss, and bone is inside that conversation whether anyone brings it up or not. Losing weight takes muscle and bone off along with the fat. What decides how much of each comes off is what you were doing while you lost it.
In a trial where older adults all followed the same diet, the group that did aerobic exercise lost several times more lean mass than the group that lifted. Both groups lost the same amount of weight. Only one of them still had its muscle at the end.
Villareal et al., New England Journal of Medicine 2017;376(20):1943–1955 · 160 adults, 6 months; lean mass −5% in the aerobic group vs −2% in the resistance group
The bone measurements from that same trial ran the same direction. The dieters doing aerobic work lost significantly more hip bone density than the dieters who lifted, with weight loss equal across the groups.
Armamento-Villareal et al., Journal of Bone and Mineral Research 2020;35(3):430–439 · same cohort, about 9% weight loss in every exercise group; total hip and femoral neck losses greatest with aerobic exercise
So the scale hands you one number and hides the only question worth asking. You can lose thirty pounds and come out of it with less muscle and less bone underneath you. You can lose the same thirty pounds with both of them intact. The kind of weight you lose is decided by whether you are lifting.
Everything above depends on one thing being true on the day. The load has to be genuinely heavy for you, on that exercise, in that session. Heavy enough changes your bone. A little under is a workout you will feel tomorrow and nothing more, and from the outside those two sets look identical.
The whole gym runs on an AI-based strength measurement system. It reads exactly what level of effort you are putting in on this repetition, today, and makes sure the weight is in the range that builds strength and muscle rather than the range that only makes you tired.
Any gym in La Habra can put a barbell in front of you. Not one of them can tell you whether the set you just finished was heavy enough to count, while the weight is still in your hands. For your bone, that has always been the only thing that mattered.
Twenty-five minutes. No charge. You walk out with your numbers.
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