Kocjan, A and Sarabon, N. The effect of unicycle riding course on trunk strength and trunk stability functions in children. J Strength Cond Res 34(12): 3560-3568, 2020-The aim of the study was to assess the effect of unicycling on trunk strength and timing of automatic stability actions of the selected trunk muscles (multifidus, obliquus externus, and erector spine). Twenty healthy 12-year-old children (12 boys, 8 girls; age 12.1 ± 0.2 years; body height 1.57 ± 0.05 m; body mass 52.8 ± 10.6 kg) were assigned to experimental and control group. Experimental group performed a supervised 12-session course of unicycling. Trunk strength was measured with a multipurpose diagnostic machine in frontal and sagittal planes in standing position. Trunk reflex responses and anticipatory actions were assessed through unexpected loading over the hands and rapid shoulder flexion, respectively. After the intervention, strength increased significantly (p < 0.01) in the experimental group in all analyzed positions. A significant interaction effect was observed during trunk extension (p < 0.01) and lateral flexion exertions (p < 0.03). Postural reflex latency improved significantly (p < 0.001) in the experimental group with a significant interaction effect in all analyzed muscles (p < 0.001). Anticipatory postural adaptations improved significantly (p ≤ 0.05) in multifidus and obliquus externus of the experimental group only. Unicycling proved to be an effective and funny tool to develop proximal stability and strength, which prevents low back pain and improves the efficiency of energy transfer between body segments. To improve the efficiency of physical education classes, unicycling should be considered a useful tool to increase trunk strength and stability among prepubertal children.