Some people can bend their fingers or limbs in seemingly impossible positions. We often refer to this unusual flexibility as double-jointedness, but physicians and researchers call it hypermobility or joint laxity.
In reality, having extra joints has nothing to do with this condition. Instead,
the increased range of motion usually comes from the soft tissue surrounding the joints – ligaments and tendons – and the joints’ shapes. Ligaments connect bones to other bones, while tendons connect muscles to bones. The elasticity of these tissues varies from person to person, influencing their flexibility. People with hypermobility often have looser ligaments, which allows for an increased range of joint movement.
The body has many different types of joints, from immovable ones in the skull to highly mobile synovial joints. Among these, the ball-and-socket joints in the shoulders and hips are the most mobile. Some people with hypermobility have ball-and-socket joints with shallower sockets, increasing their mobility.
Hypermobility can also result from the physical shape of the bones. For instance, the elbow joint consists of a hook-like bone called the olecranon fitting into a groove on the humerus. If this hook is small or the groove is deep, it allows for increased extension, sometimes leading to the appearance of hyperextended elbows.
Research indicates a genetic component to hypermobility, with identical twins more likely to display hypermobility than fraternal twins. Moreover, hypermobility tends to diminish with age and varies across different populations, with higher prevalence in women and people of African, Asian, and Middle Eastern descent.
Interestingly, studies have linked hypermobility to various physical and mental health conditions. For instance, being double-jointed has long been associated with an increased risk for asthma, irritable bowel syndrome, and other disorders. Hypermobile individuals are also more prone to anxiety, with heightened brain activity in related areas.