We compared the effects of two 8-week concurrent strength and endurance trainings (CSETs) on running economy (RE) and running biomechanics, and we explored whether the effects on running biomechanics were mediated by responder status [high vs low responder based on -2.6% change in RE]. Thirty-one male recreational runners were randomly assigned to a standard endurance running training combined with either plyometric (CSET-PLY) or dynamic body-weight (CSET-DYN) training. RE and running biomechanics [contact (t) and flight (t) time, step frequency (SF), duty factor (DF), and leg stiffness (kleg)] were measured pre- and post-intervention. RE significantly improved following CSET (RE = -2.1 ± 3.9%; p = 0.005) and no changes in t, DF, SF, and kleg (p ≥ 0.10) but a shorter t (p ≥ 0.03) from pre- to post-intervention were seen. The prevalence of high responders was 42% (RE = -5.7 ± 2.4%). Among high responders, there were no changes in running biomechanics except participants following CSET-DYN who increased their SF (+3%). These results indicate that improvements in RE obtained through CSET-PLY and CSET-DYN involve minimal to no changes in running biomechanics and that there was not a training modality, which was better than the other. More detailed biomechanical assessments involving kinematics, kinetics, and electromyography could shed light on the underlying mechanisms of RE improvement.