Adaptation behavior of skilled infant bouncers to different spring frequencies

  • Olinda Habib Perez School of Human Kinetics, University of Ottawa Current affiliation: Graduate Department of Rehabilitation Science, University of Toronto
  • Coren Walters-Stewart Department of Mechanical Engineering, University of Ottawa Current affiliation: School of Human Kinetics, University of Ottawa
  • D.G. E Robertson School of Human Kinetics, University of Ottawa
  • Natalie Baddour Department of Mechanical Engineering, University of Ottawa
  • Heidi Sveistrup School of Rehabilitation Sciences, University of Ottawa School of Human Kinetics, University of Ottawa

Abstract

Infants explore their environments through repetitive movements that are constrained or facilitated by the environmental context. In this study, we evaluated how skilled bouncers adapted to bouncing in systems with four different spring conditions (natural frequencies of 0.9, 1.15, 1.27 and 1.56 Hz). Trunk kinematics and vertical ground reaction forces (VGRFs) were recorded from three pre-walking infants (mean age 10.6 ±0.9 months). Bounce frequency, trunk displacement, peak VGRF, percent of time on the ground and time to peak force as a function of time on the ground were analyzed. In addition, infant bounce frequencies were compared to measured oscillations of an inert mass equivalent to each infant’s mass. All infants bounced above the natural frequency of the spring system in all conditions suggesting that they did not behave solely like mass-spring systems. Infants produced asymmetrical VGRF loading patterns suggesting that a timing component, such as bounce frequency, was regulated. Skilled infants consistently increased their bounce frequency as their vertical trunk displacement decreased; however, the mode for regulating bounce frequency differed from infant to infant.

Published
2015-04-30
Section
Original Article