Background: Weightlifters commonly use upper-extremity high-load training, which encompasses techniques ranging from momentary failure to non-failure. However, little is known about how this training affects posture and core endurance, despite knowing that these factors are risk factors for weightlifting injuries. Therefore, this study aimed to determine the immediate effects of upper-extremity high-load training to momentary failure versus non-failure, using the dumbbell overhead press, on posture and core endurance in recreational collegiate weightlifters. Methods: Fifty recreational weightlifters aged 18–24 with two years of upper extremity resistance training experience were recruited for this study. The participants performed dumbbell overhead press exercises under high-load failure (HL-F) and high-load non-failure (HL-NF) conditions two days after 1RM testing and calculation of the 80% 1RM load. The study analyzed postural changes using photographic data processed in Kinovea, while core endurance was assessed during a prone plank test. Standardized warm-ups, controlled exercise execution, and pre- and post-exercise assessments were conducted to measure core endurance and postural alterations. Results: The thoracic kyphosis angle, together with scapular balance angle and lateral scapular slide distance, increased significantly after HL-F compared to the unloading state, while the craniovertebral angle and prone plank time decreased significantly (p < 0.05). The HL-NF condition showed no statistically significant differences relative to the unloading measurements (p > 0.05). The unloading measurements across testing days were consistent, indicating no carryover effect (p > 0.05). Conclusions: The findings indicate that high-load training to failure adversely affects posture and core endurance, increasing fatigue and potentially increasing the risk of acute injuries. Non-failure training maintains stability, underscoring the importance of strategic program design for achieving optimal performance while minimizing adverse effects.

The effectiveness of using McGill trunk endurance scores as raw values or body-weight-normalized metrics remains uncertain for evaluating weight classes, e