How to Read a Bone Density Scan: Why Your Z-Score Depends on Your Sport
If you have had a bone density scan, there is a good chance you read the wrong number on it. Most reports lead with the T-score. For premenopausal women and men under 50, the score you generally want to pay attention to is the Z-score. For women in the menopausal transition, the picture is a little more nuanced.
A note before we start: this article explains how a medical test is constructed. It is not medical advice, and nothing here can tell you what your own result means. That is a conversation for a sports medicine physician who can see your scan, your history and your bloods. What we can do is help you understand what you are looking at, and know when to go ask.
The Number Most Athletes Read Is the Wrong One
A DXA report gives you two scores, and they answer different questions.
T-score compares your bone mineral density to a young adult reference population at peak bone mass.
Z-score compares you to people of your own age and sex.
The International Society for Clinical Densitometry is explicit about which applies to whom. Z-scores, not T-scores, are preferred for females prior to menopause and for males younger than 50. T-scores are for post-menopausal women and men aged 50 and over.
This matters because the T-score is what most reports put first, and because the T-score is the one attached to the words "osteopenia" and "osteoporosis" — words that do not apply to a 41-year-old triathlete in the way the printout implies. The ISCD is equally clear that osteoporosis cannot be diagnosed in men under 50 on the basis of bone density alone, and it does not apply the standard diagnostic criteria to pre-menopausal women either.
So: find the Z-score. That is your line.
Athlete Takeaway: If you are a premenopausal woman or a man under 50, focus on your Z-score; if you are a woman in the menopausal transition, interpretation is more nuanced and T-score criteria may also apply.
What a Z-Score Is Actually Comparing You To
A Z-score is a standard deviation score against an age- and sex-matched reference population. Zero is average for your age. Positive is above.
The clinical threshold is straightforward: a Z-score of −2.0 or lower is defined as "below the expected range for age," and anything above −2.0 is "within the expected range for age."
Here is where it gets interesting for athletes, because there is a second threshold in play. The 2023 IOC consensus statement on Relative Energy Deficiency in Sport uses a Z-score below −1 at the lumbar spine, total hip or femoral neck as a primary indicator in its clinical assessment tool for pre-menopausal women and men under 50.
Those two numbers are not in conflict — they are two different tools answering two different questions. The clinical threshold asks "is this person's bone unusual for the general population." The sports threshold asks "is this worth a closer look in an athlete." An athlete reading −1.2 as a disease has misread it. An athlete reading it as nothing at all because a clinical guideline says −2.0 has also misread it. The gap between those two numbers is exactly where a conversation with a sports medicine physician belongs.
One practical thing worth knowing. The "DXA scan" many age-group athletes have actually had is a body composition scan at a commercial studio, not a bone densitometry scan. They are different protocols. A body-comp scan may not produce a clinically valid Z-score at the standard sites, and — per the IOC consensus — scans from different machines and facilities cannot be meaningfully compared against each other. If you want to track bone density over time, ideally return to the same facility and DXA machine; results from different machines should not be treated as directly comparable unless the instruments have been properly cross-calibrated.
Athlete Takeaway: Check whether your scan was a bone densitometry scan or a body composition scan. If you plan to repeat it, book the same facility so the numbers are comparable.
New Research: The Expected Value Is Not the Same for Every Athlete
A study published in Sports Medicine in June 2026 (Stellingwerff and colleagues) went after a question that has been sitting under all of this. If bone responds to loading, and sports load the skeleton very differently, should we really be reading every athlete's scan against one general-population reference?
The researchers assessed 213 athletes — 143 women and 70 men, across 13 sports — using the IOC's clinical assessment tool, including questionnaires, bloods and DXA-derived bone density. Bone density was compared cross-sectionally across low-, medium- and high-impact loading sports, and athletes were followed prospectively for new bone stress injuries.
The findings, in the authors' own terms: spine and femoral neck Z-scores were significantly lower in low- and medium-impact sports than in high-impact sports. And crucially, that pattern held regardless of REDs traffic-light status — that is, it was not simply a downstream effect of under-fuelling.
The number that makes it concrete: among athletes assessed as zero-to-low REDs risk — athletes with no meaningful energy-availability concern — femoral neck Z-scores averaged 0.4 ± 0.9 in low-impact sports, 0.5 ± 0.9 in medium-impact, and 1.4 ± 1.0 in high-impact. A full standard deviation of difference between healthy, well-fuelled athletes, driven by what their sport asks of their skeleton.
The authors' conclusion is the practical part: practitioners should interpret bone density results in the context of an athlete's specific sport background rather than relying solely on general population norms.
Two honest caveats. This is a cross-sectional comparison in tier 3–5 athletes, so it describes elite and highly trained populations rather than age-groupers, and it cannot establish cause. And the paper is a REDs paper funded through the Women's Health, Sports & Performance Institute, with several authors employed or contracted there — worth knowing, and it does not undermine the finding.
One thing we are deliberately not telling you: which specific sports sat in which impact category. That table is behind the journal's paywall, and we are not going to guess at it — including where triathlon, cycling or swimming were placed, or whether triathlon was among the 13 sports at all. The principle is what matters here, and the principle is well supported.
Athlete Takeaway: When you discuss a scan with a physician, tell them what your training actually consists of. Sport background is now a documented part of interpreting the number.
What the Endurance Literature Already Showed — Including One Correction
None of this is new for cyclists. A systematic review of 31 studies concluded that adult road cyclists in regular training have low bone mineral density in key regions, and that competitive road cycling is less effective at improving bone mass than weight-bearing sports. The proposed mechanism is unglamorous and obvious: long hours in a weight-supported position, plus a lot of recovery time sitting or lying down.
Two details from that review are more encouraging than the headline. Adolescent cyclists showed no difference from controls — the deficit appears to accumulate over adult training years. And combining cycling with running counteracted the effect, as did off-road and sprint-oriented cycling. Multisport athletes are not in the same position as a pure road cyclist.
The swimming story needs updating, though. "Swimmers have weak bones" has been repeated for two decades on the strength of older cross-sectional work. A 2024 systematic review and meta-analysis in Sports Medicine covering 36 human studies found that bone mineral density was similar between swimmers and non-athletic controls at the lumbar spine, hip and femoral neck, with no evidence of a negative effect of swimming on other bone regions. Swimmers are low relative to impact athletes. That is not the same as low.
Which is precisely the point of this whole article. "Low" is meaningless without "compared to whom."
One caution in the other direction, because it cuts against a comfortable assumption: distance running is not automatically protective. The literature indicates cortical density relates inversely to competitive running distance, with the lowest values in long-distance runners, and runners generally sit below sprinters, gymnasts and ball-sport athletes. Having a run leg does not make you a high-impact athlete.
Athlete Takeaway: Stop asking whether your bone density is low and start asking what it is low relative to. It is a different and much more useful question.
What Actually Builds Bone — and It Is Site-Specific
The genuinely good news is that bone responds to the right stimulus, and the two effective stimuli work on different parts of the skeleton.
Heavy resistance training, for the spine. The LIFTMOR randomized controlled trial put 101 postmenopausal women with low bone mass through two supervised 30-minute sessions per week for eight months — deadlift, overhead press, back squat and jumping chin-ups with drop landings, at 5 sets of 5 reps above 85% of one-rep max. Lumbar spine density rose 2.9% against a 1.2% loss in controls. At the femoral neck the training group gained only 0.3% — so the honest reading there is prevented loss, not gain. One adverse event occurred across more than 2,600 training sessions.
The obvious caveat: that was postmenopausal women averaging 65 years old with existing low bone mass. It establishes that heavy loading can move bone in a population that was losing it. It does not establish the same magnitude in a trained 40-year-old triathlete.
Jumping, for the hip. A meta-analysis of 19 jump-training trials in adults, covering 666 participants, found a median dose of about 50 jumps, four times weekly produced a 1.50% increase in femoral neck density, and a 1.26% increase at the total hip in younger adults. It produced no significant effect at the lumbar spine.
Put those together and the coaching implication is clean: heavy lifting works on the spine, jumping works on the hip, and neither covers the skeleton on its own. Both are already things an endurance athlete should be doing for other reasons — our guides to incorporating strength into your triathlon plan and in-season strength maintenance cover how to fit them in without compromising your key sessions, and five essential lifts for every endurance athlete over 40 is a good starting point for the lifting side.
One firm exception. If you have current bone pain, a recent bone stress injury, or a known low bone density diagnosis, do not add impact or plyometric work off the back of this article. That is a conversation with a physician first, and the order matters.
Athlete Takeaway: If your training is mostly swimming and riding, add two heavy lifting sessions and a short jumping protocol each week — they load different sites and you want both.
Where Fuelling Fits — Briefly
Energy availability genuinely matters for bone, and it is the reason bone density appears in the REDs assessment at all. But the finding above is that impact loading affects bone independent of REDs status — which means bone is not only a fuelling story, and treating it as one leaves the loading half of the problem unaddressed.
If the fuelling side is the part you want to think about, we have covered it properly elsewhere: RED-S in triathlon and the subtle signs of under-fuelling are the two to read, and iron deficiency and ferritin covers a related blood-work question athletes ask at the same time.
When to Stop Reading and Book an Appointment
This is the section that matters most. Any of the following is a reason to see a sports medicine physician — not to read another article:
Recurrent or repeated stress fractures
Any bone stress injury at a high-risk site — femoral neck, sacrum or pelvis
Menstrual irregularity or absence for six months or more
A low body mass index, or a period of significant unintentional weight loss
Any previous fracture from a low-impact fall
A Z-score below −1 — particularly when accompanied by menstrual disturbance, recurrent bone stress injury, low energy availability or other REDs indicators — warrants closer clinical evaluation.
If fueling is part of the picture, a registered sports dietitian belongs in that conversation too. And to be direct about the limits of what a coach can do: we can program your training and explain how the test works. We cannot interpret your scan, and no coach should tell you a result is "fine because you're a cyclist." That sentence is the single most likely misuse of everything above, and it is not one we are making.
The Bottom Line
Bone density is a comparison, not a grade. Read the Z-score if you are a pre-menopausal woman or a man under 50. Understand that the reference population is the general public, and that new evidence shows well-fuelled athletes in low-impact sports sit around a full standard deviation below high-impact athletes at the femoral neck — a difference associated with the loading characteristics of their sports, even among athletes at low REDs risk.
Then do the two things that actually move the number: lift heavy for the spine, jump for the hip, twice a week each. And if any of the triggers above apply to you, book the appointment rather than reasoning it out yourself.
If you want strength and impact work built into your season properly — enough to matter for bone, not so much that it costs you your key sessions — set up a call with us now, and we will help you be ready for your best race day!
This article is educational and is not medical advice. It cannot tell you what your own results mean. If you have concerns about your bone health, please speak with a sports medicine physician.
