Bone Density and Osteoporosis

How bone responds to load

Bone is not scaffolding. It is living tissue that gets taken apart and rebuilt continuously, and on average your whole skeleton is replaced every eight to ten years [Osteoporosis NZ, 2024]. What decides whether it comes back thicker or thinner is largely what you asked it to carry.

The Royal Osteoporosis Society puts it in two sentences: “If you are not active, your bones lose strength. Bones get stronger when you use them.” [Royal Osteoporosis Society, 2026]

Two forces do that work. One is muscle: as a muscle contracts it pulls on the bone it is attached to, and that pull is what maintains or improves the bone's strength. The other is impact, the force that travels up through the skeleton each time a foot hits the ground [Royal Osteoporosis Society, 2026]. Lifting supplies the first. Walking, stamping and stair climbing supply the second.

The response is local. Bone that gets loaded responds; bone that does not, does not. The 2022 UK consensus statement on exercise for osteoporosis describes the effects of exercise on bone as “highly localised,” and says resistance exercises should be chosen to load “skeletal sites at risk of osteoporotic fracture, such as the spine, proximal femur and forearm” [BJSM, 2022]. Spine, hip, wrist. That is also why a daily walk, good as it is for the hips, does almost nothing for a wrist.

Until your mid-twenties, bone formation outruns breakdown. From then to about 50 the two roughly match [Osteoporosis NZ, 2024]. From 50 onward breakdown wins, and in women it speeds up through menopause as oestrogen falls [Osteoporosis NZ, 2024].

None of that closes the door. Loading still changes bone at 68. It just has to be put there on purpose, because ordinary daily life stopped supplying enough of it years ago.

What your DXA score means

A bone density scan, written DXA or DEXA, is a low-dose X-ray of your hip and spine, taken while you lie on a padded table. It runs 10 to 20 minutes and does not hurt [Osteoporosis NZ, 2026]. It returns two numbers, and the one people fix on is the T-score.

The T-score compares your bone density against a healthy young adult of the same sex. Osteoporosis New Zealand sets out the bands:

• -1.0 or higher is normal bone density.
• -1.0 to -2.4 is osteopenia: thinner than normal, not severely weakened.
• -2.5 or lower is osteoporosis [Osteoporosis NZ, 2024].

The second number, the Z-score, compares you against people your own age. Below -2.0 it suggests something other than ageing is driving the bone loss [Osteoporosis NZ, 2024].

That -2.5 line is drawn across a smooth range, not a switch. A spine at -2.4 and one at -2.6 are near enough the same spine with different labels.

Nor is the score the whole of your fracture risk. “Fragility fractures can occur in individuals with T-scores in both the osteopenic and osteoporotic ranges,” and your provider weighs the scan alongside your other risk factors before deciding anything [Osteoporosis NZ, 2024]. A bone already broken in a fall from standing height counts heavily, whatever the number says.

For training, the score does two jobs. It tells us which sites are weakest, so we know where the load goes, and it tells us how much care the spine needs. It does not set a weight, and it is no scoreboard: follow-up scans come four to five years after treatment starts [Osteoporosis NZ, 2026]. Your training changes long before the scan does.

What to train

Three things, done together rather than picked between. The 2022 consensus statement is blunt about the pairing: “The combination of impact and progressive resistance training best promotes bone strength” [BJSM, 2022].

Strength work, two or three days a week

The consensus recommends muscle-strengthening exercise on two or three days a week, and is specific about load. “For maximum benefit, muscle strengthening should include progressive muscle resistance training. In practice, this is the maximum that can be lifted 8–12 times (building up to three sets for each exercise)” [BJSM, 2022].

Read that as a target, not a starting point. The same paragraph adds that “lower intensity exercise ensuring good technique is recommended before increasing intensity levels” [BJSM, 2022]. Technique first, then load. All muscle groups get work, back muscles included, because that is what loads the spine [BJSM, 2022].

Health New Zealand asks for the same in plainer terms: at least two sessions a week, using weights, bands, or your own body weight [Health NZ, 2026].

Impact work, and the line that decides how much

This is the part that splits on your history, and it is the most useful thing on this page if you have a diagnosis.

• If you have osteoporosis but no vertebral fracture and no history of several low-trauma fractures, moderate impact is recommended on most days: stamping, jogging, low-level jumping, hopping, at least 50 impacts a session [BJSM, 2022].
• If you have had a vertebral fracture or several low-trauma fractures, impact stops at brisk walking, about 20 minutes a day, 150 minutes across the week. The statement calls this precautionary, against “theoretical (unproved) risks of further vertebral fracture in this group” [BJSM, 2022].

If you do not know which of the two you are, ask your doctor before your first session. It is not something to work out by trying.

Balance, because a fracture usually needs a fall

Bone strength decides what a fall costs. Balance decides how often you fall. The consensus recommends balance and strength work at least twice a week, naming Tai Chi, dance, yoga and Pilates [BJSM, 2022]. Our guide to strength training over 60 covers what the falls evidence shows.

What to avoid, and when to ask a doctor first

If a scan has put you at -2.5 or lower, or you have already broken a bone in a fall from standing height, talk to your doctor before you load your spine. That is not a formality. Health New Zealand asks anyone with osteoporosis to check with their healthcare provider before starting a new exercise routine, and says your provider can refer you to a physiotherapist or registered exercise professional; you can also refer yourself [Health NZ, 2026]. The Royal Osteoporosis Society is more specific: see a doctor or physiotherapist first if you have a history of many broken bones or spinal fractures, or if you are recovering from a broken bone [Royal Osteoporosis Society, 2026].

Then the movements. Specific ones, not a general instruction to be careful:

• Sit-ups and crunches, and the Pilates roll-down and curl-up. All bend the spine forward under load. The Royal Osteoporosis Society names them, and the consensus asks for alternatives to the roll-down and curl-up as a precaution [Royal Osteoporosis Society, 2026].
• Touching your toes, and any warm-up that leaves you hanging forward with a rounded back. Sustained or end-range forward bending is the pattern to change [BJSM, 2022].
• Lifting anything off the floor with a rounded back, from a dumbbell to a grandchild. Health New Zealand puts this at the top of its list, because it drives large forces through the spine and raises the risk of a vertebral compression fracture [Health NZ, 2026]. Use a hip hinge instead: bend from the hip, keep the back straight [Royal Osteoporosis Society, 2026].
• Fast or forced twisting of the trunk, especially holding something. New Zealand's guidance lists twisting the spine alongside rounded-back bending [Health NZ, 2026], while the 2022 consensus says rotation is safe “if performed smoothly and comfortably” [BJSM, 2022]. Neither says a fast, loaded wrench is fine. Turn your feet and move the whole body instead.
• High-impact, fast or jerky exercise: star jumps, jumping down from a step, anything that lands hard and unplanned [Health NZ, 2026].

Now the other error, which we see more often. Reviewing the evidence on harm, the consensus statement found “little evidence of harm, including fractures, occurring while exercising,” concluded that “exercise is therefore unlikely to cause a fracture,” and told professionals not to restrict activity on a bone density number alone [BJSM, 2022]. Doing nothing has its own cost, and it is not theoretical: with severe osteoporosis you can break a bone “doing ordinary things like bending, lifting or just getting up from a chair” [Health NZ, 2026]. A weak spine is not a protected spine.

One more thing to be plain about. Training does not replace your medication. The consensus puts exercise as “an adjunct rather than an alternative to pharmaceutical treatment where this is indicated” [BJSM, 2022], the Royal Osteoporosis Society says outright that “exercise is not a replacement for an osteoporosis medicine” [Royal Osteoporosis Society, 2026], and Osteoporosis New Zealand states that people with osteoporosis need medication to reduce their risk of future fractures [Osteoporosis NZ, 2026]. Take the medication your doctor prescribed and train as well. The consensus is explicit that exercise still belongs in the plan when someone is on treatment [BJSM, 2022].

What that looks like in our studio

Bring your most recent scan and anything your specialist has written to the first session. What they have ruled out stays ruled out. Loads start light enough that the movement is clean, and come from your strength test, not your age. On technique we use the Royal Osteoporosis Society's line: “It is how you lift rather than how much you lift that matters” [Royal Osteoporosis Society, 2026]. If you feel strain in your back, the weight goes down that set, not next week. Rebuilding the muscle around all this is covered in our guide to age-related muscle loss.