It's summertime in New Jersey. Summer camp is in full swing, sports bags are packed to capacity, and kids across Monmouth and Middlesex County are lugging gear from cars to fields to cabins and back again.
We're here to talk about how heavy or lopsided summer loads affect young bodies in the moment and help parents prevent unnecessary muscle fatigue, strain, and movement discomfort.
The loads are often heavier and the distances covered while carrying them are sometimes longer. Not to mention that the carrying style is almost always worse from a biomechanical standpoint, and the kids carrying them still have developing spines.
What Load Does to a Developing Spine
Just as external forces influence how structures bear weight, heavy or asymmetrical loads place temporary mechanical stress on a developing spine.
While carrying heavy bags does not permanently deform the spine, it forces children into acute postural adjustments, increased disc pressure, and muscle fatigue.
Bones, intervertebral discs, and postural muscles in children and adolescents are still maturing. During pubertal growth spurts, rapid linear bone elongation can temporarily outpace muscle flexibility and core stability, making the spine more vulnerable to acute strain under heavy loads.
Upright MRI studies show that while actively bearing heavy backpack loads, children experience immediate, transient compression of intervertebral discs and temporary postural shifts in spinal curvature, with heavier loads correlating with increased muscular strain and reported discomfort. Read the full report findings here.
The general guideline most pediatric organizations endorse is that a child's bag should not exceed 10-15% of their body weight, and even this threshold may be too generous for younger children. But what research consistently shows is that students carry, on average, over 15% of their body weight, triggering immediate biomechanical and postural compensations (such as forward head position and trunk lean) that increase muscular strain.
Summer camp bags routinely exceed this. A full equipment bag for a youth lacrosse player or a packed overnight duffel can easily hit 20 to 30 pounds. On a 70-pound child, that's approaching 40% of body weight.
The Problem with One-Shoulder Carrying
Unliked backpacks, summer bags almost never have two functional straps. They're duffel bags / sling bags / equipment bags with a single-shoulder carry.
Carrying a load over one shoulder can cause lateral spine bending and shoulder elevation. Research comparing one-strap and two-strap carrying found that asymmetrical loading affected both the loaded and unloaded sides of the body, altering frontal knee biomechanics and contributing to low back pain.
An important finding from the study is that the unloaded side is also affected. When a child shifts their weight to compensate for a heavy bag on one shoulder, the hip drops, the knee absorbs altered forces, and the lumbar spine bends laterally to maintain balance. Over a summer of daily carrying, that compensation pattern becomes habitual. The muscles on one side shorten while the other side lengthens and weakens.
What We See in Our Clinic
Children come in at the end of summer, or early fall, with complaints that don't have an obvious traumatic origin, e.g., neck tension, one shoulder sitting higher than the other, and/or lower back stiffness that their parents attribute to "a growth spurt." Occasionally, we’ll hear something more concrete, like a complaint of shoulder or upper back pain that started "around when camp began" and never fully went away.
What we might see on an evaluation of someone in this situation is some version of: poor posture and spinal misalignment with associated muscle strain, chronic back, neck, and shoulder pain (aka effects consistent with prolonged asymmetric load carriage during a developmental period).
The specific pattern we look for is whether the child has developed what's called forward head posture: when the head migrates forward relative to the shoulders to counterbalance a heavy posterior or lateral load. Overloaded bags cause posterior displacement of the center of gravity, generating augmented strain on the neck and back muscles. Chronic forward head posture leads to cervical muscular imbalances that, when left unaddressed, can result in upper crossed syndrome and long-term musculoskeletal dysfunction.
What Parents Can Do
- Before camp starts, weigh your child's packed bag. It should be under 10% of their body weight; for a 70-pound child, that's 7 pounds. Most summer bags don't get close to this, but being aware of the target is the starting point.
- If the bag has two straps, both should be used. If the bag is a duffel, consider whether a two-strap backpack style bag accomplishes the same purpose. The spine doesn't care about aesthetics.
- Reduce carrying time if possible. If a child has to walk a significant distance with a heavy load, breaking it into shorter trips or switching the carry side at regular intervals can help reduce asymmetric strain.
- Watch for the shoulder hike. The most observable sign of asymmetric load compensation is one shoulder sitting higher than the other, either during carrying or at rest.
While many children's musculoskeletal complaints resolve with appropriate management, experiencing low back pain as a child or adolescent can be associated with chronic low back pain in some adults.
The spine your child develops in these years is the one they'll carry for the next seven decades, which means the bag they're carrying right now may be doing more to shape it than most realize.
Want to learn more or have your child checked? Give us a call at (732) 812-5200.