When we talk about school backpacks for children, we’re not simply talking about a container for books. In reality, we’re talking about a load that is placed every day on a musculoskeletal system that is still growing—and therefore in the midst of maturing and adapting functionally. Between the ages of five and eleven, children go through a phase of extremely rapid growth. Height gain is not linear but is accompanied by gradual changes in body proportions: the length of the back changes, the ratio between the trunk and the lower limbs shifts, and the position of the center of mass—that is, the body’s center of balance—varies. The neuromuscular system continuously adapts to these changes. In this context, a non-adjustable backpack can become a potential source of instability. If the length of the back panel is not proportionate to the child’s height, the load may sit too low or too far from the back. From a biomechanical standpoint, this increases the lever arm of the weight relative to the spine. The farther the load is, the greater the torque that must be compensated for by activating the paravertebral and scapular muscles. Biomechanical studies have shown that adjusting the height of shoulder straps significantly alters the activity of the trapezius and deltoid muscles and influences posture while walking [1–3]. When the load is correctly positioned and fits snugly against the back, compensatory muscle activation is reduced and the distribution of forces along the body’s axis is more physiological. It is important to clarify a fundamental point: the adjustability of a backpack does not prevent scoliosis or “shape” the spine. However, the daily repetition of an unevenly distributed load can lead to muscle fatigue, pain, and temporary postural adaptations, especially during periods of rapid growth [4,5]. The ability to “grow” the backpack along with the child serves precisely this purpose: to prevent the body from being exposed to an unevenly distributed load for years on end. This is not an aesthetic or commercial concept, but a biomechanical principle of progressive adaptation to changes in body proportions as the child grows.

The main risk is not a single condition, but rather a state of repeated functional overload. When the weight of a backpack exceeds the musculoskeletal system’s ability to adapt, the body employs compensatory strategies. The child leans the torso forward to restore balance to the center of mass, raises the shoulders to stabilize the load, and adjusts stride length while walking. These adaptations are physiological, but they become problematic if they occur daily under excessive loads. The literature shows that high loads are more frequently associated with changes in posture and an increase in musculoskeletal discomfort [2,8–10]. Changes in trunk posture, increased plantar pressure, and alterations in gait are observed. One of the most frequently cited studies in this field has documented, using magnetic resonance imaging, a temporary reduction in the height of the lumbar intervertebral discs under load [6]. Fortunately, this compression is reversible and does not result in permanent structural damage. Asymmetry poses an additional risk factor. Unevenly adjusted shoulder straps or carrying the backpack on only one shoulder can cause spinal rotation and asymmetric muscle activation [3,7]. Over time, these compensatory mechanisms can contribute to the onset of neck or lower back pain, especially in older children. In other words, a backpack doesn’t “ruin your back.” However, it can become a source of mechanical stress when the weight, distribution, and fit are not properly adjusted.

When it comes to ergonomic backpacks, there is a risk that the term will be perceived as nothing more than a marketing gimmick. In reality, from a biomechanical standpoint, the difference between a traditional model and one designed according to ergonomic principles is substantial. A traditional backpack, lacking a frame and stabilization systems, tends to act like a weight suspended on the shoulders. While walking, the load sways, moves away from the back, and causes constant slight shifts in the center of balance. This requires greater activation of the paraspinal, scapular, and cervical muscles to maintain balance. Ergonomic backpacks are designed to integrate the load into the child’s body. The contoured back panel, proper padding, adjustable shoulder straps, and well-organized internal compartments serve not an aesthetic but a biomechanical purpose: to reduce the distance between the weight and the spine, stabilize the load, and distribute the forces more evenly. Experimental studies show that the position of the load and the design of the backpack influence spinal posture during transport and the body’s ability to maintain balance while walking [3–5]. In particular, ergonomic models result in less alteration of the physiological lumbar curve compared to traditional models. Of course, it’s not possible to completely eliminate the load, but an ergonomic backpack can distribute its impact, making the system more stable and less reliant on constant muscular compensation. Over time, this can lead to less fatigue and a greater ability to handle daily weight.

The rolling suitcase is often seen as a way to “save your back.” In reality, the issue is more complex. From a mechanical standpoint, pulling a trolley places an asymmetrical load on a single arm. The weight does not rest directly on the shoulders, but the arm doing the pulling must generate a continuous pulling force. This causes the torso to rotate compensatorily and results in an asymmetrical distribution of forces along the spine. Studies on gait analysis show that using a walker can reduce certain postural changes on flat surfaces, but it introduces lateral and rotational adaptations [8]. On stairs, uneven sidewalks, or complex paths, these adaptations may become more pronounced. Carrying a backpack symmetrically on both shoulders—provided the weight is appropriate and the fit is correct—allows for a balanced distribution of forces along the body’s axis. The spine functions in a more balanced manner, and the load on the muscles is distributed more evenly. This does not mean that a trolley is always the wrong choice: when handling very heavy loads over short, straight distances, it can be a viable alternative.

Very often, the lumbar belt and chest strap are considered secondary accessories, and sometimes even unnecessary. In reality, they are central components of the ergonomic system. A lumbar support belt helps transfer a significant portion of the load to the pelvis, a broad bony structure anatomically designed to bear weight. By reducing the load on the shoulder girdle, it decreases pressure on the shoulder straps and tension on the trapezius and cervical muscles. Biomechanical studies show that wearing a lumbar support belt reduces lumbar compression forces and alters the distribution of pressure along the spine [1,6]. This effect is particularly noticeable when walking on inclined surfaces. The chest strap, on the other hand, serves a stabilizing function. By keeping the shoulder straps in place, it limits sideways slippage and reduces backpack sway during movement [3]. This keeps the load closer to the body’s center of mass and reduces the need for muscular compensation. When these components are not used, the backpack loses a significant portion of its biomechanical effectiveness.

A value of 10% of body weight is now considered a conservative guideline supported by extensive scientific evidence [2,8–10]. It does not represent an absolute biological threshold, but exceeding this value increases the likelihood of postural changes under load and the onset of muscle pain. Studies show that significant changes in gait and foot pressure are observed even at rates exceeding 15% [8]. However, individual susceptibility varies depending on age, muscle tone, body composition, and level of physical activity. It is therefore advisable to consider the weight of the backpack as part of a comprehensive assessment that also takes into account the fit, the internal distribution of the contents, and the child’s characteristics. Placing the heaviest books close to the back reduces the torque on the spine and improves load stability [3].

Adjusting a backpack isn’t a one-time task, but a dynamic process that should evolve as the child grows. It’s often done at the start of the school year without further adjustments, even though children grow rapidly over the course of the months. Proper fit is determined not so much by aesthetic criteria as by a functional assessment of movement. From a biomechanical standpoint, the goal is to keep the backpack’s center of mass as close as possible to the body’s center of mass. When the load is too low or too far from the back, the rotational stress on the spine increases, and the child tends to compensate by leaning the trunk forward [2,3]. This leaning is an adaptive response to restore balance. On the contrary, proper adjustment keeps the body’s weight centered in the thoracolumbar region and reduces compensatory muscle activation. Another important indicator is symmetry. Unevenly adjusted shoulder straps cause trunk rotation and asymmetric muscle activation while walking [3,7]. Observing the child while walking is often more useful than a static assessment: if the backpack sways from side to side or the child noticeably changes their stride length, the fit may not be optimal.

Idiopathic scoliosis is a structural deformity of the spine with a multifactorial etiology, in which genetic and biological factors play a central role. It is therefore incorrect to claim that backpacks cause scoliosis [12]. It is essential to distinguish between postural habits and spinal deformities. Excessive strain can cause the trunk to tilt or the shoulders to rise during exertion, but these adaptations are functional and reversible. They do not represent a permanent structural curvature. On the other hand, it is possible that an ill-fitting backpack could cause muscle pain related to the load.

The concept of lightness is often misunderstood. A backpack that’s very light when empty may seem like a good thing, but if it lacks structural support, it tends to lose its shape under the weight of books, shifting the load away from your back. When the weight shifts backward, the need for compensatory muscle activation increases. Comparative studies show that backpacks with an ergonomic design and a contoured back panel cause less alteration of the lumbar curve under load than flexible models without support [3–5]. The frame is not designed to stiffen the back, but to stabilize the load. An effective stabilization system reduces sway while walking and keeps the weight close to the body’s center of mass. Ergonomic doesn't mean "heavy." The best choice, therefore, is not between “light” and “heavy,” but between “light and stable” and “light but unstable.”

Back pain in children is a multifactorial condition. The backpack is one of the contributing factors. Prolonged sedentary behavior, intensive use of digital devices in non-ergonomic postures, and low levels of physical activity are associated with a higher prevalence of low back pain [10,11]. A lack of movement limits the development of the muscles that stabilize the spine and reduces the ability to handle daily physical demands. At the other extreme, intense and poorly balanced physical activity can lead to repeated mechanical stress. Some evidence suggests a U-shaped relationship between physical activity and low back pain: both very low and excessively high levels may be associated with an increased risk [9]. What appears to be protective is moderate, regular, and varied physical activity.

Promoting daily physical activity is one of the most effective strategies for supporting the health of the developing musculoskeletal system. Moderate, varied, and age-appropriate physical activity improves muscle tone and the ability to adapt to physical demands. For school-age children, at least one hour of aerobic activity per day is recommended. Ideally, at least three days a week should include activities that strengthen muscles and bones, such as running, jumping, climbing, playing team sports, dancing, or active games. Alternating study periods with breaks for movement reduces muscle stiffness and improves postural tolerance. Paying attention to the study environment—desk height, foot support, and adequate lighting—also helps reduce the need for compensatory movements. Foot health is closely linked to weight distribution. Excessive weight alters plantar pressure and can temporarily affect gait [2,8].

One of the most common mistakes is underestimating the total weight. The backpack is packed without carefully selecting the necessary items, consistently exceeding 10% of body weight. Another common mistake is failing to adjust the straps regularly. The shoulder straps are set once and not adjusted as the child grows. Even minor asymmetries can cause trunk rotation and uneven muscle activation [3,7]. Carrying a backpack on one shoulder—a practice particularly common among preteens—exacerbates lateral imbalances and increases unilateral muscle strain. Failure to use the lumbar belt and chest strap reduces the effectiveness of the ergonomic system [1,6]. Finally, the internal arrangement of the material is often overlooked. Placing heavier books farther away from the spine increases the torsional stress on the spine [3] Prevention, in fact, doesn’t require complicated measures. What’s needed above all is attention, a few periodic checks, and a basic understanding of how the weight of a backpack affects the body.