The assessment of thoracolumbar muscle endurance (TLME) is common among strength and conditioning professionals and clinicians desiring to quantify baseline muscle performance and determine injury risk. Reference values for such assessments are documented in the literature; however, their utility may be of limited value due to heterogeneous participant selection and limited demographic reporting. Moreover, active cohorts who engage in resistance training (RT) may reach a ceiling effect on existing reference values when testing routinely trained muscles. Thus, the purpose of this study was to establish reference values for standardized TLME tests among women who participate in recreational RT and to determine whether imbalances or asymmetries exist. Participants included 61 women aged 18-59 years who engaged in RT for at least 1 year. Flexor, extensor, and lateral flexor TLME was isometrically assessed using standardized procedures with documented reproducibility (r ≥ 0.93). Results identified significant differences (p < 0.001) between mean TLME times of flexors (163 ± 106 seconds) and extensors (105 ± 57 seconds). Left (66 ± 38 seconds) and right side bridges (61 ± 33 seconds) were comparable (p = 0.06). Flexor to extensor imbalances were more pronounced among RT participants when compared with previously reported general population reference values, suggesting a training effect or bias. Moreover, similar imbalances favoring the flexors are a documented risk factor for low back pain. Thus, training considerations inclusive of the extensors may benefit women who engage in RT as a means of mitigating risk. Individuals evaluating muscle performance should consider reference values that represent the population of interest.