To compare the responses to doing strength (S) training on alternate days with endurance (E) training vs doing both types of training on the same days per week, seven young men (group A-2 d) did S and E training together in single sessions 2 d·wk−1 for 20 wk. A second group (B-4 d, N = 8) did the S training on 2 d·wk−1 and E training on 2 other d·wk−1. S training was six to eight sets of 15–20 RM on a leg press weight machine. E training was six to eight 3-min bouts of cycle ergometer exercise at 90–100% JOURNAL/mespex/04.02/00005768-199006000-00012/ENTITY_OV0312/v/2017-07-20T222237Z/r/image-pngO2max B-4 d (25%) increased leg press 1 RM more (P < 0.05) than A-2 d (13%), but the groups increased similarly (A-2 d, B-4 d) in knee extensor (31%, 34%) and flexor (12%, 14%) cross-sectional area and vastus lateralis mean fiber area (33%, 25%). Increases in JOURNAL/mespex/04.02/00005768-199006000-00012/ENTITY_OV0312/v/2017-07-20T222237Z/r/image-pngO2max (7%, 6%), repetitions with 80% 1 RM (39%, 64%), repetitions with the pre-training 1 RM (33, 55), and PFK (19%, 10%) and LDH (15%, 23%) activity did not differ (P > 0.05) between groups. CS activity increased significantly only in A-2 d (26%; B-4 d, 6%). It is concluded that same day (vs different day) concurrent strength and endurance training may impede strength development without impeding hypertrophy. On the other hand, same day training may enhance increases in CS activity but not JOURNAL/mespex/04.02/00005768-199006000-00012/ENTITY_OV0312/v/2017-07-20T222237Z/r/image-pngO2max or weight lifting endurance.