The common phrase "double-jointed" is a misnomer, according to medical experts. What people typically refer to as being "double-jointed" is actually a condition known as joint hypermobility, where joints can move beyond the typical range of motion.
"Double joints aren’t real," Dr. Maryellen Brucato, a board-certified foot and ankle surgeon, told HuffPost. "You do not possess extra joints anywhere in your body. When someone describes themselves as ‘double-jointed,’ what they actually have is hypermobility." Hypermobility means a person's joints stretch and move far beyond the normal baseline, even though they have the same skeletal structure as everyone else.
This increased range of motion is due to differences in the body's connective tissues, which include ligaments, tendons, and fascia. These tissues act like cables tethering bones together. In hypermobile individuals, these tissues are more lax and stretchy, allowing for greater joint movement. "Hypermobile folks tend to have a mix [of collagen] that’s a little more elastic and a little less tough. Think rubber band versus shoelace," explained Dr. Nicholas Belasco, a sports medicine physician.
Hypermobility is more common than many realize, with estimates suggesting it affects between one in 10 and one in three people, depending on the criteria used for measurement. Doctors often assess for it using tests like the Beighton score, which checks for the ability to bend certain joints beyond typical limits.
Genetics play a significant role in hypermobility, often stemming from inherited conditions that affect collagen production, such as Ehlers-Danlos syndrome (EDS). While some people develop increased flexibility through training, true hypermobility is typically an inherited trait. The condition tends to be more prevalent in children and women, and some research also suggests a potential link with folate metabolism.
While hypermobility might seem like a harmless quirk, it can lead to various health issues. The instability in hypermobile joints can make individuals more susceptible to injuries like recurrent ankle sprains and chronic pain. "Loose joints are less stable, so your muscles have to do more of the work holding things together," Belasco noted. This can also affect proprioception, the sense of where joints are in space, further increasing injury risk.
Some people with hypermobility also experience symptoms that affect multiple body systems, including postural orthostatic tachycardia syndrome (POTS) and mast cell activation syndrome (MCAS). "You have a body with unique performance characteristics and capabilities that can be advantageous... But a Ferrari also requires specialized maintenance," said Dr. Jacques Courseault, a physical medicine and rehabilitation physician.
Experts advise seeking medical evaluation if hypermobility is accompanied by chronic joint pain, frequent sprains, joint dislocations, unexplained fatigue, dizziness, or symptoms affecting multiple body systems. While many people grow out of hypermobility as they age, the underlying connective tissue differences may persist. For those experiencing issues, strength and balance training can be beneficial, and in some cases, custom orthotics may be necessary to manage excessive motion and prevent long-term damage.