['The present study investigated associations between trunk muscle strength, jump performance, and lower limb kinematics during drop jumps on stable and unstable surfaces. Next to this behavioral approach, correlations were also computed on a neuromuscular level between trunk and leg muscle activity during the same test conditions.', 'Twenty-nine healthy and physically active subjects (age 23 ± 3 years) were enrolled in this study. Peak isokinetic torque (PIT) of the trunk flexors and extensors was assessed separately on an isokinetic device. In addition, tests included drop jumps (DJ) on a force plate under stable and unstable (i.e., balance pad on top of the force plate) surfaces. Lower limb kinematics as well as electromyographic activity of selected trunk and leg muscles were analyzed.', 'Significant positive but small correlations (0.50 ≤ r ≤ 0.66, p < 0.05) were detected between trunk extensor PIT and athletic performance measures (i.e., DJ height, DJ performance index), irrespective of surface condition. Further, significant negative but small correlation coefficients were examined between trunk extensor PIT and knee valgus motion under stable and unstable surface conditions (-0.48 ≤ r ≤ -0.45, p < 0.05). In addition, significant positive but small correlations (0.45 ≤ r ≤ 0.68, p < 0.05) were found between trunk and leg muscle activity, irrespective of surface condition.'] Does role of the trunk during drop jump on stable and unstable surfaces?