Abstract and Introduction
Abstract
Although obesity has been linked to several differences in walking mechanics, few studies have examined movement mechanics of overweight and obese (OW/OB) children performing higher impact activities, such as running.
Purpose: The purpose of this study is to determine differences in running mechanics between healthy weight (HW) children and children classified as OW/OB.
Methods: Forty-two children (17 OW/OB, 25 HW) ran overground while kinematic and kinetic data were recorded using a motion capture system and force plate. Kinematic variables of interest included stance time, step length, and frontal and sagittal plane joint angles and excursions at the hip, knee, and ankle. Kinetic variables of interest included ground reaction forces and hip, knee, and ankle moments in the sagittal and frontal planes.
Results: The OW/OB group spent more time in stance, took shorter steps, displayed less hip flexion during the first half of stance, had greater ankle inversion at foot strike, had greater knee abduction throughout stance, and had smaller knee flexion, knee adduction, and hip adduction excursions. In comparing unscaled ground reaction forces, the OW/OB group displayed greater peak vertical force, vertical impact peaks, and vertical loading rates. The OW/OB group also displayed greater unscaled plantar and dorsiflexion moments, knee flexion and extension moments, ankle inversion moments, and knee and hip abduction moments.
Conclusion: These data suggest that increased body weight in children is associated with changes in running mechanics. Higher joint moments and ground reaction forces may indicate increased injury risk or the development of joint degeneration among overweight/obese children.
Introduction
The prevalence of childhood obesity throughout the world has become a major health concern. The health risks associated with childhood obesity include cardiovascular disease, metabolic syndrome, depression, and social isolation.[1] In addition to the negative physiological and psychological effects, excessive weight in children has been linked to movement disfunction, excessive joint loading, and the development of osteoarthritis and other joint pathologies.[1–6]
Several differences in kinematics, ground reaction forces, and joint loading have been reported when comparing walking mechanics of healthy weight (HW) children to children classified as overweight and obese (OW/OB). Children classified as OW/OB display slower self-selected walking speeds, greater time spent in double support, shorter step lengths, and greater step width compared with HW children.[7,8] These gait characteristics are typical of individuals trying to reduce energy expenditure or who have increased instability during walking. In the frontal plane, obese children display greater hip adduction moments and knee abduction angles and moments during the stance phase of walking.[9–12] Repetitive stresses on the hip and knee joint due to greater joint excursions and moments in the frontal plane can result in increased joint loading to the lateral facet of the tibia and increased strain on the anterior cruciate ligament (ACL), patellofemoral pain, and ultimately disability.[4,13,14] In the sagittal plane, obese children display decreased hip and knee joint flexion and increased extensor moments and greater leg stiffness during stance compared with HW children.[8,9,13,15] The combination of decreased hip and knee flexion and increased leg stiffness has been associated with increased joint loading.[6] The differences in walking mechanics between obese and nonobese children are cause for concern. Although mechanical loading is necessary for proper bone growth and muscle development in children, excessive loading may lead to joint injuries, joint degenerative diseases, and/or pain. Furthermore, the additional joint stress has been suggested to lead to musculoskeletal injury and malalignments in obese children, including slipped capital femoral epiphysis and tibia vara, respectively,.[16–18]
Although obesity has been linked to several differences in joint kinematics and kinetics and increased vertical loading during walking, few studies have examined movement mechanics of OW/OB children performing higher impact activities, such as running. It is likely that many of the differences between OW/OB and HW children during walking will also exist for running, but with greater magnitude.[17] In a sample of healthy adults, tibiofemoral contact forces were 2–3 times greater in running compared with walking.[19] Similarly, youth (11–18 yr) classified as obese display greater nonnormalized frontal and sagittal plane knee moments during running when compared with HW youth.[17] In addition, prepubescent children display significant increases in peak pressure and maximum force on the foot as they increase their gait speed from walking to running.[7,20]
Running is one of the most popular and common forms of exercise recommended to reduce obesity and improve health. However, there are only a few known studies that have examined running mechanics in prepubescent children.[3,7,20] These studies primarily focused on comparing plantar pressure differences between OW/OB and HW children. They reported that both OW/OB and HW children display significant increases in peak plantar pressure on the foot when going from walking to running.[7,20] In addition, a positive relationship between peak plantar pressure and body mass index (BMI) was observed.[3] When directly compared with HW children, OW/OB children on average displayed up to 25% greater peak vertical force (FZmax) and 45% greater peak pressure on the foot during running.[7] Rubinstein and colleagues[7] suggest that obesity-related changes to plantar loading could place OW/OB children at greater risk of overuse injuries. Increased plantar loading has been associated with flatter arches, increased foot pain, and increased risk of fractures to the foot.[3,7,20,21] Increased foot pressure in children has also been associated with increased sedentary time and decreased moderate–vigorous physical activity.[22] Although elevated plantar pressure observed in OW/OB children running suggests greater vertical loading compared with HW children, plantar pressure does not provide any information on lower extremity joint kinematics and kinetics. By examining both running kinematics and kinetics of OW/OB children, greater insight can be provided on the potential risks that running may have for these children. Therefore, a running analysis using motion capture and ground reaction forces is needed to capture more fully the differences in running mechanics between OW/OB and HW children.
The purpose of this study is to determine differences in running mechanics between OW/OB and HW children. Based on the movement mechanics and plantar pressure data observed in obese children during walking and running, we hypothesize that OW/OB children will display higher vertical loading during running compared with HW children. Furthermore, we expect joint moments to be higher for the OW/OB children. Lastly, we expect decreased sagittal plane angles and excursions and increased frontal plane angles and excursion at the knee, and ankle joints in the OW/OB group during running. We expect no group differences in hip angles and excursions. Understanding the differences in running mechanics between OW/OB and HW children can help to identify potential risk factors associated with OW/OB children running. Furthermore, teachers, parents, and other clinicians will be better equipped in prescribing appropriate physical activities for OW/OB children that can safely meet the recommended physical activity guidelines for children.
Med Sci Sports Exerc. 2021;53(10):2101-2110. © 2021 American College of Sports Medicine
