Effects of frequency on single leg hopping in typically developing preadolescents

Hopping is considered a mass-spring model movement in which the leg supports the center of mass. There is a preferred hopping frequency and hopping outside of that frequency is more difficult and requires more energy. Leg stiffness has been shown to be an important factor when hopping at different frequencies in young adult populations. The purpose of this study was to observe how a still-developing preadolescent population would modify leg stiffness while hopping at different frequencies and if they have similar motor control strategies compared to young adults. The subjects hopped on their dominant leg to the beat of a metronome at one of four frequency conditions based on their calculated preferred frequency, MP (preferred frequency), MM (20% increase), MF (40% increase), and MS (20% decrease). It was found that this population could change their hopping frequency and they achieved this by manipulating their leg stiffness. At the higher frequency conditions there was less movement of the toe and the center of mass in both the vertical and horizontal directions, including decreased hopping height, decreased COM displacement and COM range of motion. Preadolescents demonstrated an adult-like ability to increase leg stiffness and modulate movement of the toe and the COM while adapting to a range of hopping frequencies. This ability could translate into other mass-spring model movements such as running and jumping