Carrying heavy backpacks can lead to back pain, altered posture and even structural damage in young children. An alternative to the traditional backpack is the wheeled backpack.
These researchers compared the impact of weight on posture and joint mechanics of school-age children carrying a traditional backpack or pulling a wheeled backpack.
The researchers recommend wheeled backpacks as a safer alternative to traditional backpacks when the load is less than 20% of a person’s body weight.
What do you carry with you to school each day? Notebooks, lunch, a book, maybe even textbooks? No matter what you pack in your bag before school, the
American Occupational Therapy Association
recommends that children and adolescents carry backpacks that weigh no more than 10% of their body weight. This means that a 100-pound child should not carry more than 10 pounds in their backpack.
Figure 1. Sample child’s backpack without waist belt
Many students find that carrying more than the recommended weight is unavoidable.
Studies
have shown that many students exceed these recommendations every day. The problem is that consistently heavy backpacks can lead to back pain and altered posture. Even if these symptoms do not show up right away, it is possible that structural changes due to backpack use can lead to back and joint pain later in life.
An alternative to the traditional backpack is the wheeled backpack that students roll behind them like a suitcase. However, few studies have compared the wheeled backpack to the traditional backpack, and there are currently no weight recommendations for wheeled backpacks.
Figure 2. Picture of wheeled backpack
For this reason, Dr. Eva Orantes-Gonzalez and a team of colleagues at the University of Granada in Spain decided to investigate how these two types of backpacks impacted the
posture
and joint
mechanics
of school-age children.
To better understand this research, let’s first explore how we walk. Walking consists of many motions and movements that propel our bodies forward (or backward). These same movements occur again and again in cycles, known as the
gait cycle.
One gait cycle is defined as the period beginning when one foot touches the ground and ending when that same foot touches the ground again.
The gait cycle is broadly divided between two phases:
stance phase
and
swing phase.
During the stance phase, the foot remains in contact with the ground, whereas during the swing phase the foot is not in contact with the ground. Each phase has different components defined by the position or movement of the foot, as shown in Figure 3.
A second way the gait cycle can be categorized is whether one or two feet are on the ground.
Single support phase
refers to the time when only one foot is on the ground, while
double support phase
means that both feet are on the ground.
One way that
gait kinematics
varies from person to person is the percentage of the gait cycle that is spent in each condition: stance phase, swing phase, single support phase, and double support phase. Another way that gait kinematics varies is in the movement of the joints while walking. The amount of movement can be quantified by measuring the angles the joints create.
In this research, Dr. Orantes-Gonzalez and colleagues quantified the gait cycle and joint angles of participants to see how they changed under different conditions. The conditions included control (no backpack, no weight), carrying a backpack loaded with 10, 15, and 20% of each participant’s body weight, and rolling a wheeled backpack filled with 10, 15, and 20% of each participant’s body weight.
Figure 4. Participant walking on the walkway (control) [Source: Eva Orantes-Gonzalez]
In total, 49 elementary school students participated in this study: 26 girls and 23 boys. The average age was 9.5 years for girls and 10.4 years for boys. The researchers took the height and weight of each student and placed 48 reflective markers at different points on the body including the head, neck, spine, pelvis, knees, and ankles.
Figure 5. Marker placement on each participant and their joints [Source: Eva Orantes-Gonzalez]
The movement of the markers was captured by twelve infrared cameras, as shown below:
In the experiment, students had one minute to walk along a 15-meter (49 feet) walkway at their own pace. Students did this a total of eight times: once to adjust to the walkway, and then once for each of the seven conditions listed above (control, traditional backpack with 10, 15, 20% body weight, wheeled backpack with 10, 15, 20% body weight). The students rested for three minutes in between each trial. The cameras were set up at the middle of the walkway to capture gait kinematics during continuous walking, avoiding the periods of acceleration and deceleration, as shown below:
After each student had completed all the trials, the researchers analyzed the data they had collected. One of the surprising findings was the observation of extra rotation in the spine of participants carrying traditional backpacks with 10% and 20% of their body weight. In other words, no matter how heavy the backpack, it negatively affected the kinematics of the spine. The researchers found that the use of a wheeled backpack was more similar to normal walking, and few kinematic adaptations were observed until the weight in the wheeled backpack was 20% of the participant’s body weight. Based on these results, the researchers recommend wheeled backpacks as a safer alternative to traditional backpacks when the load is less than 20% of body weight.
Figure 6. Participant walking on the walkway rolling a wheeled backpack [Source: Eva Orantes-Gonzalez]
These first experiments were focused only on walking on flat surfaces. We know that students also go up and down stairs, among other types of movement. In future experiments, Dr. Orantes-Gonzalez and her team hope to expand this research to observe the kinematics of carrying backpacks under other conditions. In addition, Dr. Orantes-Gonzalez plans to collect data on the body’s
metabolism
to see how carrying a backpack can affect oxygen use. Finally, Dr. Orantes-Gonzalez hopes to include older populations in this research including high school and college students.
Dr. Orantes-Gonzalez understands that spine health is not always the most important criteria for students when choosing a backpack. “We find that students in elementary school will readily use wheeled backpacks, but when they get to high school they’ll opt for a more traditional backpack. Wheeled backpacks aren’t seen as cool.” Nevertheless, it is important for students to understand these decisions can have lifelong impacts on the health of their bones and joints.
Dr. Orantes-Gonzalez is a Research Fellow in the Faculty of Physical Activity and Sport at the University of Granada in Granada, Spain. She began her career as an elementary school teacher and the health of school-age children continues to be a research focus of hers. When not in the laboratory, Dr. Orantes-Gonzalez enjoys spending time outdoors and with her family.
For More Information:
Orantes-Gonzalez, E. et al. 2019. “A kinematic comparison of gait with a backpack versus a trolley for load carriage in children.” Applied Ergonomics, 80: 28-34.
Orantes-Gonzalez, E. and J. Heredia-Jimenez. 2019. “Gait asymmetry and rating of perceived exertion: How are they influenced by carrying a backpack and pulling a trolley?” Work, 63: 253-9.
Orantes-Gonzalez, E. and J. Heredia-Jimenez. 2017. “Pulling a school trolley: a good kinematic option for children.” Gait & Posture, 53: 61-66.
Orantes-Gonzalez, E. et al. 2016. “Children require less gait kinematic adaptations to pull a trolley than to carry a backpack.” Gait & Posture, 52: 189-93.
Dr. Eva Orantes-Gonzales and Dr. Jose Heredia Jiménez, Eva’s thesis supervisor.
Dr. Eva Orantes-Gonzalez presenting a poster on her research at the International Congress of the International Society of Biomechanics in July 2019 in Calgary, Canada.
