Increased and decreased joint range of motion (ROM) are modifiable risk factors for musculoskeletal soft-tissue injuries. Certain heritable disorders of connective tissue, which have a unifying symptom of joint hypermobility, are caused by mutations within the COL5A1 gene. Furthermore, the COL5A1 BstUI restriction fragment length polymorphism (RFLP) sequence variant is associated with ROM measurements in a mixed injured/uninjured cohort. The association between COL5A1 BstUI RFLP and sit and reach (SR) ROM in an apparently healthy and physically active cohort was investigated. The SR test was performed on 325 white subjects (204 males). Subjects were also genotyped for the BstUI RFLP (C/T) within the 3′-untranslated region of the COL5A1 gene. The COL5A1 BstUI RFLP genotype was associated with SR ROM in older (≥35 years) subjects (TT: 225 ± 96 mm, TC: 245 ± 100 mm, CC: 32 ± 108 mm, N=96, P=0.017). Age and COL5A1 BstUI genotype interacted significantly for SR ROM. Sex and COL5A1 genotype accounted for 22.8% of the variance in SR ROM in the older group. The COL5A1 BstUI RFLP is associated with SR ROM, particularly with increasing age and is an important contributing factor to ROM variation, particularly in older, apparently healthy and physically active individuals.