There is a number that every cyclist over 35 should know: 84%. That is the proportion of competitive cyclists who meet the criteria for osteopenia or osteoporosis, according to a systematic review of 31 studies published in PMC. For context, the rate among matched non-athletes is 50%. Cycling — the sport you chose partly because it is low-impact and easy on the joints — is quietly degrading your skeleton.
This is not speculation. The data is extensive, consistent, and largely ignored by the cycling community.
Why cycling starves your bones
Bone is not static. It is living tissue that continuously remodels itself in response to mechanical demand. The mechanism is well understood: osteocytes — the sensor cells embedded in bone — detect strain from external loading and signal osteoblasts to build new bone tissue. Remove the loading, and the signal disappears. Osteoclasts — the cells that break down bone — continue working, and the net balance shifts toward loss.
Cycling removes almost every stimulus that drives bone formation. You are seated. Your feet are clipped into pedals. Your body weight is distributed across saddle, handlebars, and pedals in a way that virtually eliminates the gravitational loading that walking, running, and standing provide by default. A four-hour ride produces enormous cardiovascular and muscular stress but near-zero osteogenic stimulus.
The systematic review data is stark. After controlling for age and body weight, cyclists are seven times more likely to have osteopenia of the spine than runners. Seven times. The lumbar spine and femoral neck — the two sites most vulnerable to fracture in later life — show the most pronounced deficits.
Three additional factors compound the problem for cyclists.
Calcium loss through sweat. Endurance exercise produces substantial sweat-related calcium loss. A two-hour ride in warm conditions can deplete calcium stores meaningfully, and if dietary intake does not compensate, the body draws calcium from the skeleton to maintain blood calcium levels. This is not a theoretical concern — it is a measurable, session-by-session withdrawal from bone mineral reserves.
Cortisol elevation. Prolonged endurance training raises cortisol, which is catabolic to bone tissue. Chronic cortisol elevation — the kind produced by consistent high-volume cycling — suppresses osteoblast activity and accelerates bone resorption. Cyclists who train ten or more hours per week have higher cortisol exposure than almost any other athlete demographic.
Low body weight. Lean cyclists carry less gravitational load through their daily activities. A 65 kg cyclist walking to the kitchen is providing less osteogenic stimulus than an 85 kg non-athlete doing the same thing. The pursuit of low body weight for climbing performance directly opposes the conditions that maintain bone health.
What running does differently
Running produces ground reaction forces of two to three times body weight with every stride. At a cadence of 170-180 steps per minute, that is 5,100 to 5,400 high-force loading events in a 30-minute run. Each impact sends a mechanical signal through the tibia, femur, pelvis, and spine that bone tissue cannot ignore.
Research consistently shows that runners have 5 to 10 percent higher bone mineral density at the hip and spine compared to the general population. That advantage is dose-dependent: higher cumulative impact exposure correlates with greater bone density, up to a plateau beyond which additional running volume provides diminishing returns.
The osteogenic response to impact loading is site-specific and frequency-dependent. Bone responds most strongly to novel, intermittent, high-force stimuli — precisely the kind of loading that running provides and cycling does not. Interestingly, the osteogenic stimulus from running is most potent in the first few minutes of a session. Research on bone mechanotransduction suggests that sensitivity to loading decreases after the initial bout of impacts as osteocytes become temporarily desensitised. This means shorter, more frequent runs are more effective for bone health than infrequent long runs.
That is good news for cyclists who dread long running sessions.
How much running is enough
The volume required for meaningful bone density improvement is lower than most cyclists assume. The research points to a practical threshold.
Frequency: Two to three sessions per week. Bone remodelling is a slow process — the full cycle of resorption and formation takes roughly four to six months — and consistent, repeated stimulus matters more than any single session. Three 20-minute runs per week outperforms one 60-minute run for bone adaptation.
Duration: 20 to 30 minutes per session. This provides sufficient loading events (3,400-5,400 impacts per session depending on pace) to trigger osteogenic signalling without the fatigue cost that would compromise cycling training.
Intensity: Moderate — conversational pace, roughly 60-70% of maximum heart rate. Higher-intensity running produces greater ground reaction forces and slightly more osteogenic stimulus, but the injury risk for cyclists who are new to running makes high-intensity work a poor trade-off. Easy running still loads the skeleton substantially.
Surface: Grass, bark trails, and well-maintained dirt paths reduce peak impact forces while still providing sufficient osteogenic stimulus. Pavement is not harmful per se, but it increases injury risk for cyclists whose musculoskeletal system is not adapted to running. Treadmills are a reasonable option in poor weather but produce slightly lower ground reaction forces than overground running due to the belt absorbing some impact energy.
Timeline: Measurable improvements in bone mineral density take 6 to 12 months of consistent running. This is not a quick fix. Bone remodelling is a slow process, and the studies that show significant results involve six months or more of regular impact exercise. The commitment required is less about intense effort and more about sustained consistency.
The calcium and vitamin D angle
Running alone is necessary but not sufficient for optimal bone health. The nutritional substrate matters.
Calcium: Current guidelines recommend 1,000-1,200 mg of calcium per day for adults, with the higher end appropriate for athletes with high sweat rates. Most cyclists do not hit this target. Dairy products, fortified plant milks, leafy greens, and tinned fish with bones are practical sources. Calcium supplementation is reasonable for cyclists who cannot consistently meet dietary targets, particularly during high-volume training blocks when sweat losses are elevated.
Vitamin D: Required for calcium absorption. Blood levels of 25-hydroxyvitamin D below 30 ng/mL are associated with impaired bone turnover. Cyclists who train predominantly indoors or live at northern latitudes are at particular risk for deficiency. A 25-hydroxyvitamin D blood test is the only way to know your status. Supplementation of 1,000-2,000 IU per day is a common recommendation for athletes with suboptimal levels, but the correct dose depends on baseline status and individual absorption.
Protein: Adequate protein intake supports the collagen matrix of bone. The same 1.6-2.2 g/kg/day recommendation that applies to muscle maintenance also supports bone health. Cyclists in a calorie deficit are at particular risk for both muscle and bone loss if protein intake is insufficient.
These nutritional considerations are not running-specific. They apply to any cyclist concerned about bone health. But combining impact loading from running with adequate calcium, vitamin D, and protein creates the conditions for bone remodelling that cycling alone categorically cannot.
What about strength training
Weight-bearing strength exercises — lunges, step-ups, loaded carries, single-leg work — provide some osteogenic stimulus. The forces involved are substantial and load the relevant skeletal sites. For cyclists who already have a gym programme, that work is contributing to bone health even if it was prescribed for other reasons.
But strength training alone does not replicate the frequency and distribution of impact loading that running provides. A strength session might produce 100-200 high-force loading events across 45 minutes. A 30-minute run produces thousands. The sheer volume of impacts, spread across the tibia, femur, pelvis, and lumbar spine, is something that gym work cannot match in practical terms.
The most effective protocol for a cyclist's bone health combines running with strength training. Two to three short runs per week plus two strength sessions that include lower-body, weight-bearing exercises creates redundant osteogenic stimulus across multiple loading patterns. Neither alone is as effective as both together.
Getting a baseline
If you have been cycling exclusively for five or more years and you are over 35, a DEXA scan is worth the investment. DEXA measures bone mineral density at the hip and spine and provides a T-score that compares your density to a healthy young adult reference population. A T-score between -1.0 and -2.5 indicates osteopenia. Below -2.5 is osteoporosis.
Knowing your starting point determines urgency. A cyclist with a T-score of -0.5 has room to improve with running and nutrition over a year or two. A cyclist with a T-score of -2.0 needs to act immediately — the fracture risk at that level is not abstract. A crash at 40 km/h with osteopenic bones produces a different outcome than the same crash with healthy bone density.
DEXA scans are widely available, relatively inexpensive, and involve minimal radiation. If you have never had one, get one. It is probably the most important health screening a lifelong cyclist can do.
The gap between what you feel and what is happening
The insidious part of cycling-related bone loss is that it is completely silent. You feel strong. You feel fit. Your cardiovascular system is in excellent shape. There are no symptoms of osteopenia until a fracture occurs. Many cyclists discover their bone density status the hard way — a collarbone fracture from a crash that would not have broken a runner's collarbone, or a stress fracture from a minor impact.
The 84% figure from the systematic review is not about professional cyclists doing 30-hour training weeks. It includes competitive amateurs — the demographic reading this. If you ride six to ten hours per week and have done so for a decade, the probability that your bone density is below where it should be is high.
Running is not the only solution. But it is the most accessible, most well-evidenced, and most time-efficient impact-loading activity available to cyclists. Twenty minutes, three times per week, on grass. The time cost is trivial. The structural benefit, over years, is substantial.
The first 5K guide provides a conservative eight-week build for cyclists who have never run or have not run in years. The injury prevention checklist covers the specific vulnerabilities that cyclists carry into running.
If you want structured guidance on building running into your training alongside your cycling programme, the Roadman community on Skool is where riders work through exactly this kind of planning.
Related reading: The Mental Health Case for Cyclists Who Run