In this study, we investigated whether a heavy strength training program, as an additive to an endurance running program, would cause significant improvements in 3-km run time in a group of recreationally fit women when compared with endurance-only (EO) training. Sixteen women aged between 18 and 27 years of age were randomly assigned to either an EO group (n = 9) or a concurrent strength and endurance (CSE) group (n = 7). A 10-week training program for both groups consisted of an endurance running program performed three afternoons per week. The CSE group also participated in strength training on the morning of each running session. Testing was conducted pre and post training in a 3-km time trial and measured JOURNAL/jscr/04.02/00124278-200803000-00011/ENTITY_OV0312/v/2017-07-20T235340Z/r/image-pngo2peak, running economy, muscular strength (1 repetition maximum), and body composition and girth. There was a trend (P = 0.07) toward greater improvement in 3-km performance time for the CSE group (106.7 ± 91.4 seconds) when compared with the EO group (77.3 ± 93.0 seconds). Further, the CSE group showed an increase in strength levels when compared with the EO group. The CSE group showed significant increases (P ≤ 0.05) in the parallel squat and hamstring curl, and a significant increase (P ≤ 0.05) was also found in upper body strength for the bench press (11.9% increase) when compared with the EO group. There were no significant differences between the two groups for JOURNAL/jscr/04.02/00124278-200803000-00011/ENTITY_OV0312/v/2017-07-20T235340Z/r/image-pngo2peak, running economy, body composition, or girth measurements. This study found no negative or compatibility problems when heavy strength training was added to an endurance running program, and a nonsignificant increase in improvement for 3-km times was evident.