Mechanical work-canceling strategy modulates initial push-off force depending on vertical jump height

In this study, we examined how jumping strategy changes with increasing vertical jump height from the viewpoint of mechanical work performed on center of mass (CoM) by individual sources (e.g., ground reaction force and gravity) during the countermovement period; we expected that intensity of the countermovement action would change with increasing jump height in a certain manner (e.g., linear relationship), which could be reflected in the changes of the outcome force and/or the work done by each of the individual sources through the countermovement. Six healthy young subjects were instructed to stand upright with both hands on their hips (akimbo posture) and to jump straight up to five different height levels, guided by black markers attached on a ceiling pole. The lowest and highest markers were located at 191 cm and 221 cm from the ground level, respectively. Kinematic and kinetic data obtained from the regular trials were used to estimate mechanical power and work, which were then analyzed to understand the change of the countermovement jump strategy with increasing vertical jump height. We found that 1) mechanical work-canceling strategy modulates initial push-off force depending on the vertical jump height, 2) the initial push-off force was directly determined by asymmetric momentum transformation, and 3) the momentum transformation may be conducted under consideration of accommodating biomechanical constraints.