Judo coaches aim to develop left-handed techniques in right-handed judoka due to a potential frequency-dependent strategic advantage during competition. Thus, easily completed tasks are needed to track the progression of the lateral preference index (percentage as right-handed actions). Thirty naïve volunteers performed two tasks, an unopposed repetition-based dynamic task (yakusoku geiko) and an opposed-bouts task (randori), before and after eight-week training protocols differing in the executing side. Training protocols consisted of a control group (without any instruction regarding the practice side), a bilateral group (practicing with both dominant and nondominant sides), and a nondominant group (practicing exclusively on the nondominant side). ANOVA-type tests were used for analyzing the suitability of the unopposed repetition-based dynamic task for detecting changes in the lateral preference index and for analyzing the concordance between tasks. Additionally, concordance was tested with Spearman’s rank correlations and Bland-Altman plots. Lower lateral preference indices (i.e., reductions of executions as right-hander) were observed after training in the nondominant group and in comparison with the control group and bilateral group on the posttest (p < 0.05). ANOVA-test for concordance analysis revealed no differences between tasks (p > 0.05) with significant correlations (p < .05) and low bias during the pretest (ρ = 0.563; bias: 4.29, 95% LoA: -36.32-27.74%) and the posttest (ρ = 0.718, bias: 0.69, 95% LoA: -39.37-40.77%). In conclusion, an unopposed repetition-based dynamic task detected reductions in lateral preference index after an eight-week nondominant training period. These results agreed with those observed with the opposed-bouts task. This indicates the eligibility of yakusoku geiko for coaching delivery due to general suitability of the unopposed repetition-based dynamic task to track the maintenance or progression of left-handedness in judo trainees.

• An unopposed repetition-based dynamic task (yakusoku geiko-based test) is able to detect reductions in lateral preference index after 8 weeks of nondominant training sessions. In this sense, this test was able to track the progression into left-handedness or the maintenance of right-handedness depending on the analyzed group.

• This test was as good as a task based on opposed-bouts (randori), indicating an overall concordance in comparison with such an open environment task. Thus, yakusoku geiko is an alternative option as valid and effective as an open environment task to analyze the lateral preference of judo trainees.

• Yakusoku geiko provides the same information as the randori but in a less time-consuming manner under a closed environment while demands less physical effort from the trainee.