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This study examined changes in intra-abdominal pressure and trunk activation during drop jump and the influence of those factors on performance. Intra-abdominal pressure (IAP) and surface electromyography (EMG) activity from the rectus abdominis (RA), transversus abdominis-internal oblique (TrA-IO) and erector spinae (ES) muscles were measured in seven males (22.3±1.0 years) during double-leg drop jumps from a 0.4m height. Development of IAP (ΔIAP) and normalized rmsEMGs were calculated in the pre-contact, impact and push-off phases, after divided by ground reaction force data. TrA-IO activation which occurred prior to ground contact were the earliest and strongest compared to other muscles activation during each phase. ΔIAP during the impact phase coincided with the peak vertical force. There were significant positive correlations between ΔIAP, TrA-IO activation and vertical force per weight. In addition, the contact time correlated negatively with ΔIAP, TrA-IO activation and vertical force per weight. These findings indicate that ΔIAP and TrA-IO activation may contribute to trunk stability and efficient landing during double-leg drop jump.