Advancing the concept of technical ability of force application in sprint acceleration

Technical ability of force application (sagittal force vector orientation) is considered a performance determinant in sprint acceleration, yet the underlying kinematics require further investigation. Sixteen elite male bobsleigh athletes performed unresisted and resisted (85 kg sled push) accelerations initiated with full effort, while ground reaction forces and kinematics were recorded for ground contacts 1 to 5. Ratio of forces (RF), body position, centre of mass velocity components, and lower limb segment rotations were examined for correlations and differences between acceleration tasks. RF was significantly associated with body position (unresisted: r = .82, p < .001; resisted: r = .83, p < .001) and extensional velocity components (unresisted: r = .83, p < .001; resisted: r = .90, p < .001). There was also a significant correlation between body position and extensional velocity component (unresisted: r = .98, p < .001; resisted: r = .84, p < .001) regardless of acceleration task. Shank orientation significantly explained variance in body position (unresisted: adj. R² = .86, p < .001; resisted: adj. R² = .81, p < .001). Resisted acceleration provoked greater RF and forward orientations as well as higher shares of extensional velocity components. To improve technical ability, practitioners should focus on manipulating body position to increase the extensional velocity component as well as on shank segment rotation in preparation for the ground contact phase.