Comparison of whole-body vertical stiffness and leg stiffness during single-leg hopping in place in children and adults.
In the hopping literature, whole-body vertical stiffness and leg stiffness are used interchangeably, due to most of the movement occurring in the vertical direction. However, there is some anterior/posterior movement of the center of mass and displacements of the foot during hopping in place in both children and adults. Further it is not understood if leg stiffness show a similar pattern as whole-body vertical stiffness when increasing hopping frequency. The purpose of this study was to test if whole-body vertical stiffness and leg stiffness are different during single-leg hopping in-place in children and adults, across a range of frequencies. Seventeen children aged 5-11years and 16 young adults participated in this study. The subjects hopped at their preferred frequency as well as 20% below, 20% above and 40% above preferred frequency. Our results demonstrate that both whole-body vertical stiffness and leg stiffness increase when increasing hopping frequency for children and adults. However, whole-body vertical stiffness consistently overestimates leg stiffness due to a similar peak force but a greater leg length change compared to vertical COM displacement. This suggests a considerable horizontal COM movement from landing to mid-stance during hopping. Children aged 5-11years old showed lower absolute values but higher normalized values of two stiffness measures than adults. This suggests somewhat adult-like stiffness control in children, but a reduced ability to manipulate the horizontal movement during single-leg hopping in place when compared to adults.
Department of Kinesiology and Health, Georgia State University, Atlanta, GA, USA.
Matthew
M
Beerse
Department of Kinesiology and Health, Georgia State University, Atlanta, GA, USA; Center for Pediatric Locomotion Sciences, Georgia State University, Atlanta, GA, USA. Electronic address: jwu11@gsu.edu.
Jianhua
J
Wu
D000328:Adult; D001696:Biomechanical Phenomena; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D011187:Posture / Q000502:physiology; D055815:Young Adult
Center of mass; Kinematic; Kinetic; Spring-mass model