Backpacks and Back Problems
Repetitive movement patterns with or without loading completed during work, recreational activity, and exercise programming can cause negative compensation due to the development of muscular imbalance and biomechanical adjustments in the kinetic chain. Many exercise enthusiasts, often lacking guidance from a qualified personal trainer, engage in resistance training programs that are not conducive to promoting a functional skeleton due to emphasis on particular prime movers without consideration for the functional chain. This eventually causes biomechanical adjustments that can limit range of motion, reduce functional capacity, and induce pain. Repetitive loading in the occupational setting is another common source for mechanical displacement from repetitive actions such as routinely carrying or moving equipment specific to the job (e.g. massage table for a massage therapist who performs home visits, or right to left loading sequences for assembly line workers). In particular, posterior and lateral loading are problematic. Research has indicated the repetitive use of backpacks has specifically demonstrated detrimental effects on the musculoskeletal system in the young and old alike. Personal trainers should be cognizant of repetitive loading patterns encountered in the daily activities of their clients to potentially offset the negative effects through appropriate counter development, stability, and flexibility training.
A number of specific studies have examined the effects of constantly using a heavy backpack during primary, secondary, and collegiate-level educational pursuits. As a whole, it has been concluded that backpack weight should not surpass 15% of one’s body weight, and the optimal position for back health is not actually against the back at all. It lies anterior to the spine at the thoracic vertebrae level (similar to an infant front pack). One study implemented by the University of Cincinnati used a cross-sectional survey to attain backpack-related data from 871 students, between the ages of 10 and 18. The survey accumulated data pertaining to the features of backpacks carried, self-perceived backpack weight, duration of use, posture during use, and any related pain. The survey results indicated that 99% of students carry backpacks, 83% carry their backpack over their shoulders, 50% perceived their backpack as heavy, 46% indicated that they carry the backpack load for 10-20 minutes at a time, multiple times per day, and 33.5% complained of pain due to backpack use. The study results also suggested that simply managing weight-based controls of backpacks (limiting backpack weight) may not be sufficient to eliminate perceived pain due to other factors such as associated posture compensations with their use.
A study published in the journal Ergonomics looked in detail at the biomechanical shifts caused by wearing a backpack at differing trunk positions. Changes of spinal curvature and repositioning error when carrying a backpack loaded at 15% of body weight was examined for the following positions; posterior to the trunk at T7, T12, and L3, and anterior to the trunk at T7, T12, and L3. A relatively smaller change was observed when the backpack was placed anterior to the trunk with the center of gravity (COG) aligned with T12. A complementary study published in the journal Spine looked at the effects of backpacks weighing approximately 10%, 20%, and 30% of body weight (with the COG aligned with T2) on the lumbar spine. Measures were taken via an upright magnetic resonance imaging (MRI) scanner. All of the backpack loads caused significant lumbar disc compression and lumbar asymmetry (as defined as the angle between the superior endplates of S1 and L1). Lumbar curvature asymmetry reached angles greater than 10° when using 8 kg backpack loads (approximately 20% body weight). The finding could potentially be extrapolated to many scenarios such as single side carry bags and related asymmetrical loading; likewise in professional environments where loads are moved from location to location. Interestingly, during study, acute back pain was alleviated when the positioning of the load was rotated periodically between anterior and posterior positions. Personal trainers may want to educate clients to counteract any significant anterior/posterior loading by being conscious of the loading and balancing it when possible. Likewise personal trainers should program anterior-posterior kinetic chain balance exercises as a routine part of the exercise prescription and encourage lateral loading as well. Movement of resistance during common exercise is an easy start to enacting this concept.
Considering the present research on routine trunk loading, it is quite evident that personal trainers may wish to include questions pertaining to daily repetitive loading in an initial client interview. This could allow for the development of an exercise prescription that promotes total-body muscle balance even in the presence of imbalance from activities of daily living. Additionally, adding trunk stabilization and asymmetrical loading drills to a client’s program will promote a healthier trunk. In most cases, a weak anterior chain along with poor spinal stability is the problem; and more crunches and back extension exercises would be a weak answer. Instead, it is recommended to use more tibial loaded sequences including overhead lifts (overhead walking lunges) and asymmetrical loading (single shouldered sand bag step-ups). Likewise, select trunk exercises that include hip management like hanging leg raises and rollouts. All of these exercises have demonstrated greater activation of the trunk compared to the conventional approach.