Ballistic performances are determined by both the maximal lower limb power output (P_max ) and their individual force-velocity (F-v) mechanical profile, especially the F-v imbalance (FV_imb ): difference between the athlete's actual and optimal profile. An optimized training should aim to increase P_max and/or reduce FV_imb . The aim of this study was to test whether an individualized training program based on the individual F-v profile would decrease subjects' individual FV_imb and in turn improve vertical jump performance. FVimb was used as the reference to assign participants to different training intervention groups. Eighty four subjects were assigned to three groups: an "optimized" group divided into velocity-deficit, force-deficit, and well-balanced sub-groups based on subjects' FV_imb , a "non-optimized" group for which the training program was not specifically based on FV_imb and a control group. All subjects underwent a 9-week specific resistance training program. The programs were designed to reduce FV_imb for the optimized groups (with specific programs for sub-groups based on individual FV_imb values), while the non-optimized group followed a classical program exactly similar for all subjects. All subjects in the three optimized training sub-groups (velocity-deficit, force-deficit, and well-balanced) increased their jumping performance (12.7 ± 5.7% ES = 0.93 ± 0.09, 14.2 ± 7.3% ES = 1.00 ± 0.17, and 7.2 ± 4.5% ES = 0.70 ± 0.36, respectively) with jump height improvement for all subjects, whereas the results were much more variable and unclear in the non-optimized group. This greater change in jump height was associated with a markedly reduced FV_imb for both force-deficit (57.9 ± 34.7% decrease in FV_imb ) and velocity-deficit (20.1 ± 4.3%) subjects, and unclear or small changes in P_max (-0.40 ± 8.4% and +10.5 ± 5.2%, respectively). An individualized training program specifically based on FV_imb (gap between the actual and optimal F-v profiles of each individual) was more efficient at improving jumping performance (i.e., unloaded squat jump height) than a traditional resistance training common to all subjects regardless of their FV_imb . Although improving both FV_imb and P_max has to be considered to improve ballistic performance, the present results showed that reducing FV_imb without even increasing P_max lead to clearly beneficial jump performance changes. Thus, FV_imb could be considered as a potentially useful variable for prescribing optimal resistance training to improve ballistic performance.

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