The term “growing pains” describes benign, recurring aches in a child’s limbs, typically occurring late in the day or at night. These symptoms are often attributed to rapid physical development, though this link is scientifically unproven. When an 18-year-old experiences similar deep, aching leg pain, they may wonder if they are having a final episode of this childhood phenomenon. To answer this, it is necessary to examine the official definition of growing pains and compare it with the biological reality of skeletal maturity in late adolescence.
Defining Growing Pains
Growing pains are medically classified as Benign Nocturnal Limb Pains of Childhood. This condition is characterized by an aching or throbbing sensation, usually felt in the muscles of the calves, front of the thighs, or behind the knees, but generally not in the joints themselves. The pain is typically bilateral, affecting both legs, and its onset is in the late afternoon or evening, sometimes waking a child from sleep. A defining feature is that the pain is completely gone by the following morning, and the child is active and pain-free during the day.
The condition most commonly affects children between the ages of three and five, and again between eight and twelve years. Despite the name, there is no scientific evidence suggesting this pain is directly caused by bone growth or growth spurts. Instead, the pain is thought to be related to muscle fatigue from intense physical activity, hypermobility, or possibly psychological stress, and it is considered a diagnosis of exclusion.
Why the Term Is Misleading for Young Adults
The idea of “growing pains” at age 18 is misleading because the rapid skeletal growth phase of childhood has largely concluded by late adolescence. Bone elongation occurs at the growth plates (epiphyseal plates), which are layers of cartilage near the ends of the long bones. Skeletal maturity occurs when these growth plates fuse completely, turning the cartilage into solid bone, which stops longitudinal growth.
This fusion process is largely complete by age 18 in most individuals, though timing varies by sex and bone. While some growth plates, such as those in the upper femur, may not completely fuse until age 20, the rapid growth spurts associated with childhood are over. Therefore, leg pain at age 18 is highly unlikely to be the benign, self-limiting condition of childhood, and it points to a different underlying cause.
Common Reasons for Leg Pain at Age 18
Since true growing pains are ruled out, leg discomfort in an 18-year-old is typically musculoskeletal, neurological, or vascular in origin. Overuse injuries are a frequent culprit, as repetitive stress from sports or exercise can lead to specific inflammatory conditions. These conditions are distinct from growing pains because they are localized, often worsened by activity, and cause a persistent ache that does not resolve overnight.
Overuse Injuries
Common overuse injuries include shin splints (medial tibial stress syndrome), which cause pain along the inner edge of the shin bone due to muscle inflammation. Tendinopathy is chronic inflammation or degeneration of a tendon, such as patellar tendinitis, resulting in pain below the kneecap. Stress fractures are also a concern for athletes or military recruits, where repeated force causes a tiny crack in the bone.
Mechanical and Neurological Issues
Mechanical issues frequently emerge in this age group. Sciatica is pain radiating down the leg from a pinched nerve in the lower back, causing a sharp, shooting, or tingling sensation. Muscle fatigue and cramps from dehydration or electrolyte imbalances are common during intense physical activity. Pain may also result from underlying mechanical alignment problems, such as flat feet or differences in leg length, which place undue stress on muscles and joints.
When Pain Requires Medical Attention
While many causes of leg pain in young adults are treatable with rest and conservative care, certain symptoms require prompt medical evaluation. Persistent or worsening pain that does not improve after several days of home treatment should always be reviewed by a doctor.
Seek immediate medical attention if the pain involves:
- Pain consistently localized to a single joint, such as the knee or hip.
- Noticeable swelling, redness, or warmth over the affected area, potentially indicating infection or a blood clot.
- A persistent limp or the inability to bear weight.
- Pain that is present in the morning and throughout the day.
- Systemic symptoms like an unexplained fever or significant fatigue.
- Pain coupled with a cold or pale leg, which suggests a circulatory issue.