Purpose: This study aimed to quantify and compare lumbar region kinetics in kick and flat serves performed by elite, adolescent male players with and without a history of low back pain (LBP). Lumbar region kinematics, as well as racquet velocity and the position of the ball at impact, was described to facilitate kinetic data interpretation.
Methods: Twenty Tennis Australia adolescent male players participated; 7 had a history of disabling LBP and confirmed L4/L5 injury and 13 were age-, height-, mass-, and performance-matched controls. The VICON motion analysis system was used to record racquet, upper and lower limb, trunk, and lumbar movement during three “flat” and three “kick” serves. A customized mathematical model calculated lumbar region kinetics/kinematics, racquet velocity, and ball position at impact, and these are reported as if all players were right-handed. A series of 2 × 2 mixed-model ANOVA were used to compare between pain/no pain and kick/flat serves.
Results: There was no significant difference in racquet velocity or ball position at impact between pain groups or serve types. The players with LBP reported significantly greater (mean difference = 1.5 N·kg−1) peak left lateral force than the control group. The flat serve was associated with significantly greater flexion moments (mean difference = 2.7 N·kg−1) than the kick serve.
Conclusions: The lumbar region undergoes substantial loading during both the kick and the flat tennis serves, including lateral flexion forces approximately eight times those experienced during running. Given that these left lateral flexion forces are significantly greater in players with a history of disabling LBP and occur simultaneous with peak vertical force and extension and right lateral rotations, this may be an important LBP mechanism in this population.