Lockie, RG, Dawes, JJ, Kornhauser, CL, and Holmes, RJ. Cross-sectional and retrospective cohort analysis of the effects of age on flexibility, strength endurance, lower-body power, and aerobic fitness in law enforcement officers. J Strength Cond Res 33(2): 451–458, 2019—There can be a great age range in cohorts of law enforcement officers. As the tasks required of officers generally do not change with advancing age, it is important to understand how physical performance in tests that assess job-specific characteristics may be altered. Retrospective analysis of performance test data of 383 officers (362 men and 21 women) was conducted. The tests included the following: sit-and-reach to determine hamstring and lower back flexibility; maximal push-up and sit-up repetitions in 60 seconds to measure muscle endurance; vertical jump (VJ) to assess lower-body power; and 2.4-km run to ascertain aerobic capacity. Data were stratified by age into 20–29, 30–39, 40–49, and 50–59 year groups, and analyzed by sex. A 1-way analysis of variance with the Bonferroni post hoc test was used to calculate the differences between the groups. Considering the male subjects, the 40–49 and 50–59 year groups performed poorer in the VJ, sit-up test, and 2.4-km run compared with the 20–29 year group (p ≤ 0.001–0.045). For the female subjects, the 20–29 year group was superior to the 30–39 (p = 0.013) and 40–49 (p = 0.025) year groups in the push-up test. To ensure that an older officer can successfully complete occupation-specific tasks, lower-body power, abdominal strength, and aerobic training should be completed. Female officers should also attempt to maintain relative upper-body strength. Practitioners must attempt to design training programs that fit within the context of the occupational demands, and potentially using a nontraditional training design as law enforcement officers may not have the time to follow a traditional periodization model.