Under controlled laboratory conditions, the average force needed to snap an adult human collarbone is roughly 1,500 newtons, which converts to about 340 pounds of force. That figure comes from cadaveric testing published in the Journal of the Medical Association of Thailand, but treating it as a single fixed number misses a lot of what actually determines whether a collarbone breaks. Speed of impact, angle, age, sex, bone density, and muscle tension all shift the threshold considerably, sometimes by a factor of two or more.
Where the 340-Pound Figure Comes From
The most commonly referenced number is from a Thai biomechanical study that loaded cadaveric clavicles to failure. The average fracture load was 1,526 newtons, and the breaks consistently occurred at the middle third of the bone, right where the gentle S-curve changes direction.1PubMed. The clavicular fracture: a biomechanical study of the mechanism of clavicular fracture and modes of the fracture In everyday units, that is about 343 pounds of force. This was a quasi-static test, meaning the force was applied slowly and steadily rather than in a sudden impact. That distinction matters enormously, as you will see below.
Other biomechanical studies have tested clavicles in different ways. One loaded 20 cadaveric clavicles to failure under both axial compression (simulating a side-impact car crash pushing the shoulder inward) and three-point bending (more like a frontal crash loading pattern), developing response corridors for each.2PubMed. Development of structural and material clavicle response corridors under axial compression and three point bending loading for clavicle finite element model validation The results are reported as corridors rather than single numbers because individual clavicles vary wildly in geometry, density, and curvature. Two clavicles from different donors tested in the same rig can produce peak forces that differ by hundreds of newtons. That variability is a genuine feature of the bone, not a problem with the testing.
Why Impact Speed Changes Everything
Bone is a rate-dependent material, which is a technical way of saying it behaves differently depending on how fast you load it. Push on a clavicle slowly and it bends before it snaps. Hit it at crash speed and it resists more force initially but then fails more abruptly. A probabilistic fracture study quantified this gap: the force at which there is a 50 percent chance of fracture is about 2,335 newtons (roughly 525 pounds) under slow loading but jumps to around 3,045 newtons (about 685 pounds) under dynamic, crash-speed loading.3Biomedical Engineering: Applications, Basis and Communications. Probabilistic Assessment for Clavicle Fracture Under Compression Loading: Rate-Dependent Behavior
That may seem counterintuitive. If the bone is stiffer at higher speeds, shouldn’t it break more easily? The stiffness means the bone absorbs more energy before it deforms. In a fast collision, the clavicle essentially becomes a harder strut: it transmits more load before giving way, but when it does break, the failure is more sudden and explosive. In real-world falls and crashes, the dynamic figure is more relevant than the slow-loading number, because people almost never break a collarbone in slow motion.
The practical difference is enormous. The 340-pound figure from the Thai study uses slow loading, while the dynamic threshold is closer to 685 pounds. Depending on which study and loading rate you reference, the answer to “how many pounds to break a collarbone” can range from about 340 to nearly 700 pounds. Neither number is wrong; they simply describe different scenarios.
How Sex and Anatomy Shift the Threshold
Men and women have measurably different clavicles. Research using cadaveric specimens found that the female clavicle tends to be shorter, less curved, and contains a lower concentration of calcium than the male clavicle.4PubMed. Anatomy of the clavicle and the intramedullary nailing of midclavicular fractures All three of those differences point in the same direction: lower fracture resistance. A shorter bone with less curvature has a smaller moment arm to distribute compressive loads, and lower calcium content means less mineral stiffness in the cortex. The same study found side-specific differences too, meaning your dominant-side clavicle is not necessarily identical to the other one.
These anatomical differences also matter for how the bone breaks. The S-shape of the clavicle is not decorative; it is a load-distributing feature. The middle third, where the curve transitions from the lateral (shoulder-side) bend to the medial (chest-side) bend, is the thinnest cross-section and the weakest point structurally. That is why roughly 70 to 80 percent of clavicle fractures in adults occur in this mid-shaft zone, regardless of how the force was applied. A smaller, less-curved clavicle concentrates stress even more tightly in this transition zone.
Children’s Bones Play by Different Rules
If you are asking this question about a child, the numbers above do not apply directly. Young bone is more elastic and less mineralized than adult bone. Instead of snapping cleanly, a child’s clavicle often undergoes what is called a greenstick or plastic bending fracture: the bone bends and cracks on one side while the other side merely deforms without breaking through.5Ovid. Plastic Bending Fractures in Children – Section: Abstract These incomplete fractures require less force than a full adult break, but the bone’s elasticity also provides a protective buffer. A child who falls on an outstretched hand transmits force to the clavicle, but the bone absorbs and distributes some of that energy through deformation rather than catastrophic failure.
This elasticity is why children’s clavicle fractures generally heal faster and with less complication than adult fractures. The periosteum, the dense membrane wrapping the bone, is thicker and more metabolically active in children, helping to generate new bone rapidly. Most pediatric clavicle fractures heal within three to six weeks with nothing more than a sling.
Clavicle Fractures During Birth
The collarbone is one of the most frequently broken bones during delivery, accounting for the vast majority of birth-related fractures. A large study found that clavicle fractures made up about 89 percent of all fractures associated with birth.6PubMed. Difficult birth is the main contributor to birth-related fracture and accidents to other neonatal fractures The forces involved are much lower than those in the adult studies described earlier, because neonatal bone is softer and thinner. A newborn’s clavicle can fracture during normal vaginal delivery, especially when the shoulders are broad relative to the birth canal.
Significant risk factors include vaginal delivery, a prolonged second stage of labor, high birth weight, and macrosomia (being larger than average for gestational age). Maternal vitamin D deficiency was also flagged as a significant contributor in one analysis.7PubMed Central. Clavicular Fractures in Newborns: What Happens to One of the Commonly Injured Bones at Birth? – Section: Results This makes biological sense: maternal vitamin D levels influence how well the fetal skeleton mineralizes. A less-mineralized neonatal clavicle would be weaker even before accounting for delivery mechanics.
Despite how alarming it sounds, neonatal clavicle fractures almost always heal without intervention. The newborn’s rapid bone remodeling capacity means the fracture site typically forms a visible callus within a week or two and is fully healed within a month. In many cases, the fracture is not even detected until a parent or pediatrician notices the callus bump.
Older Adults and Bone Density Loss
At the other end of the age spectrum, osteoporosis and age-related bone loss lower the fracture threshold substantially. The cortical shell of the clavicle thins with age, and mineral density declines, meaning the same fall that would bruise a 30-year-old’s shoulder might snap a 75-year-old’s collarbone. Clinical experience and epidemiological data show a second peak in clavicle fracture incidence among older adults, distinct from the well-known peak in young active men. In elderly patients, the fracture often results from a simple ground-level fall rather than a high-energy collision.
The sex-based anatomical differences mentioned earlier compound this problem in postmenopausal women, whose accelerated bone loss means the already-thinner, lower-calcium female clavicle becomes progressively weaker. No cadaveric study has published a clean pounds-of-force threshold specifically for osteoporotic clavicles, but the clinical picture is clear: the threshold drops enough that everyday low-energy falls become a realistic fracture mechanism.
Why the Middle Third Always Breaks First
Regardless of age, sex, or impact direction, the middle third of the clavicle is overwhelmingly the most common fracture site. The biomechanical study from Thailand confirmed this, with fractures occurring right at the transition between the lateral and medial curves.1PubMed. The clavicular fracture: a biomechanical study of the mechanism of clavicular fracture and modes of the fracture Think of it like bending a paper clip: the metal does not snap at the thick ends, it snaps at the thinnest point along the bend. The clavicle’s mid-shaft has the smallest cross-sectional area and no nearby muscle attachments thick enough to buttress it, making it the structural weak link.
Lateral-third fractures (near the shoulder joint) and medial-third fractures (near the sternum) do occur, but each represents only about 10 to 15 percent of cases. They tend to involve different injury patterns: lateral fractures are more common from direct blows to the top of the shoulder, while medial fractures are rarer and typically involve high-energy trauma like motor vehicle crashes. The treatment considerations differ for each location, but the underlying reason the mid-shaft breaks preferentially is geometry, not bad luck.
What Happens When a Collarbone Fracture Goes Wrong
Most clavicle fractures heal without lasting problems, but the bone sits directly above some critical anatomy. The subclavian artery and vein run just behind the clavicle, and the brachial plexus, the nerve bundle controlling the entire arm, passes underneath it. When a fracture displaces significantly or when sharp bone fragments shift, these structures can be damaged. Neurovascular complications can show up immediately after the fracture, develop gradually as fragments shift or callus forms, or even result from surgical repair itself.8PubMed Central. Neurovascular Complications Associated With Clavicle Fractures: A Report of Three Cases and Recommendations
Delayed surgical fixation raises the risk of brachial plexus injury, which underscores why badly displaced fractures often receive prompt operative treatment rather than a wait-and-see approach. The vast majority of clavicle fractures do not cause vascular or nerve damage, but it is worth understanding that the collarbone is not just a structural strut connecting the shoulder to the trunk. It is also a protective shield for the vessels and nerves below it, and when that shield breaks, the things it was protecting become vulnerable.
Post-Repair Strength Is Not the Same as Original Strength
If your clavicle has been surgically repaired, you might wonder whether the bone returns to its original strength. Biomechanical testing of repaired clavicles found that the failure torque, the twisting force needed to re-break the bone, was significantly lower after both plate fixation and intramedullary nail repair compared to an intact clavicle. An intact clavicle failed at an average torque of about 36.5 newton-meters, while plate-repaired clavicles failed at around 18 newton-meters and nail-repaired ones at about 21.5 newton-meters.9PubMed. Stability of mid-shaft clavicle fractures after plate fixation versus intramedullary repair and after hardware removal In other words, the repaired bone was roughly half as strong in torsion as the original, regardless of which fixation method was used.
This testing was done with the hardware still in place. Hardware removal, which some patients request after healing to eliminate discomfort or a visible bump, potentially reduces strength further since the screw holes remain as stress concentrators in the cortex. The clinical reality is that re-fracture after plate removal is uncommon but recognized, and surgeons typically advise waiting until the fracture site has fully remodeled before removing hardware. Biologically healed bone eventually fills in the screw holes, but the timeline for full structural recovery extends well beyond the point where you feel “healed.”
Car Crashes and Seat Belt Design
The automotive safety world thinks about clavicle fracture thresholds constantly, because the collarbone is one of the structures that absorbs load from a seat belt in a frontal collision. Standard three-point belts route the shoulder strap diagonally across the clavicle and chest. In a crash, the belt restrains the torso, and the clavicle takes a share of that restraining force. Research into four-point seat belt systems (an X-shaped harness) found that the alternative design shifted more load onto the clavicles and pelvis and away from the chest, cutting chest deflection roughly in half.10SAE International. Biomechanics of 4-Point Seat Belt Systems in Frontal Impacts
That trade-off captures the engineering dilemma nicely: a belt that reduces fatal chest injuries by spreading the load more broadly may increase the risk of clavicle fracture. For crash engineers, a broken collarbone is an acceptable outcome compared to a crushed sternum or ruptured aorta. Finite element computer models are now used to simulate shoulder impacts and predict whether a given crash scenario will fracture the clavicle in a specific individual. One study using geometrically personalized models (built from actual CT scans of test subjects) correctly predicted clavicle fracture in four out of six lateral-impact scenarios, with the model being conservative in the remaining two cases.11PubMed. Clavicle fracture prediction: simulation of shoulder lateral impacts with geometrically personalized finite elements models Personalized models like these are inching closer to the goal of predicting, before a crash ever happens, which occupants are at higher risk based on their shoulder geometry.
Why No Single Number Answers the Question
If you wanted one number to take away, somewhere between 340 and 700 pounds of force is the range most adult clavicles fail under, depending on loading speed. But that range is wide enough to be almost useless for individual prediction. Your personal threshold depends on your bone mineral density, the exact geometry of your clavicle, your age, your sex, whether you braced your muscles before impact (contracted muscles around the shoulder girdle can absorb energy and reduce the load transmitted to the bone), and the direction and speed of the force. An elderly woman with osteoporosis might fracture at a fraction of the low end of that range. A young, well-muscled man might withstand well above the high end.
What the research does make clear is that the collarbone breaks more easily than many people assume. It is a slender, exposed, S-shaped bone with no significant surrounding muscle padding at its weakest point. Compared to the femur, which requires thousands of pounds of force to break in a healthy adult, or the tibia, which sits behind the shin’s soft tissue, the clavicle is structurally modest. That modesty is partly by design: in evolutionary terms, a bone that breaks before the rib cage or spine absorbs catastrophic force is acting as a mechanical fuse, protecting more critical structures at its own expense.
Stress Fractures and Repetitive Loading
Not all clavicle fractures come from a single traumatic event. Stress fractures of the clavicle have been documented in athletes who subject the bone to repetitive loading, particularly in sports involving overhead motion or rowing. These fractures develop gradually as microdamage accumulates faster than the bone’s remodeling process can repair it. The force in any single stroke or lift may be nowhere near the acute fracture threshold, but thousands of repetitions at sub-threshold force can produce the same end result. Stress fractures of the clavicle are uncommon compared to those in weight-bearing bones like the tibia or metatarsals, but they are well-recognized in the sports medicine literature and are sometimes initially misdiagnosed as muscle strains because the onset is gradual rather than sudden.
For anyone worried about clavicle strength, whether because of a previous fracture, osteoporosis risk, or participation in contact sports, the honest answer is that no non-invasive test will tell you your personal fracture threshold in pounds. What you can do is maintain bone density through weight-bearing exercise and adequate calcium and vitamin D intake, strengthen the muscles of the shoulder girdle to act as energy absorbers, and wear appropriate protective gear during high-risk activities. The collarbone does its job remarkably well for its size, but it remains one of the easiest bones in the body to break when force finds it at the wrong angle and speed.