Background and Aim: Lower crossed syndrome (LCS) is a common postural dysfunction among individuals with sedentary lifestyles; however, it can also affect athletes due to sport-specific demands. This study aimed to investigate and compare the effects of core stability exercises (CSE) and National Academy of Sports Medicine (NASM) exercises on lumbar lordosis, pelvic tilt, and trunk muscle endurance in athletes with LCS. Methods: This study employed an experimental design with pretest and posttest assessments across three groups. Thirty-six male athletes with LCS (aged 20–30 years) were randomly assigned to three groups: the CSE group, the NASM group, and the control group. Participants in the experimental groups performed their respective exercise protocols for 8 weeks (3 sessions per week). Lumbar lordosis and pelvic tilt angles were assessed using a flexicurve and a pelvic inclinometer, respectively. Additionally, the McGill test was used to determine the endurance of the trunk muscles. Results: Both exercise protocols significantly decreased the lumbar lordosis angle and pelvic tilt, and significantly increased the endurance of the trunk flexors and extensors (p < 0.05). However, the NASM protocol significantly increased the lateral trunk flexors on both the dominant side (p < 0.001) and the nondominant side (p = 0.005). Additionally, the findings revealed that the effects of 8 weeks of exercise on the lordosis angle (F(2, 33) = 0.153, p = 0.85, ηp² = 0.009), pelvic tilt (F(2, 33) = 2.01, p = 0.15, ηp² = 0.109), trunk flexor endurance (F(2, 33) = 2.875, p = 0.07, ηp² = 0.148) and extensor endurance (F(2, 33) = 1.246, p = 0.301, ηp² = 0.07) did not differ significant between the NASM and CSE group (p > 0.05); However, a significant difference was observed in the endurance of trunk lateral flexors on the dominant (F(2, 33) = 16.897, p < 0.001, ηp² = 0.506) and nondominant sides (F(2, 33) = 16.931, p < 0.001, ηp² = 0.506) among the groups and post hoc Tukey tests revealed that the NASM group exhibited significantly greater improvements than the CSE group (p < 0.001). Conclusions: An 8-week of core stability and NASM exercise program are recommended to reduce the lumbar lordosis angle and pelvic tilt and to improve the endurance of trunk flexors and extensors in athletes with LCS. Although only the NASM protocol increased the endurance of lateral trunk flexors on both the dominant and nondominant sides, no significant difference was observed between the two exercise protocols regarding the other variables.
