Objective: To compare muscle strength and flexibility among a subgroup of women with extension-related chronic nonspecific low back pain (CNLBP) with healthy controls. Methods: In this case-control study, 32 subjects with and without extension-related CNLBP were tested (n = 16 in each group). Gluteal, abdominal, paravertebral, and hamstring strength, along with hip flexor flexibility and hamstring flexibility were compared between groups. Data were analyzed using the Mann¿Whitney test (p < .007). Results: The CNLBP subgroup displayed significantly lower strength of all muscles analyzed (p < .007), with the exception of gluteus medius. The flexibility of the hip flexors and hamstrings were not significantly reduced among the women with CNLBP (p > .007). Discussion: The present study showed that alterations in muscle strength, but not flexibility, partly consistent with those previously hypothesized but not objectively reported, were present among a subgroup of women with extension-related CNLBP. These results may have implications for the selection of therapeutic exercises among this subgroup of people with CNLBP.