Fyfe JJ, Bishop DJ, Zacharewicz E, Russell AP, Stepto NK. Concurrent exercise incorporating high-intensity interval or continuous training modulates mTORC1 signaling and microRNA expression in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol 310: R1297-R1311, 2016. First published April 13, 2016 doi:10.1152/ajpregu.00479.2015.-We compared the effects of concurrent exercise, incorporating either high-intensity interval training (HIT) or moderate-intensity continuous training (MICT), on mechanistic target of rapamycin complex 1 (mTORC1) signaling and microRNA expression in skeletal muscle, relative to resistance exercise (RE) alone. Eight males (mean Ϯ SD: age, 27 Ϯ 4 yr; V O2 peak, 45.7 Ϯ 9 ml·kg Ϫ1 ·min Ϫ1 ) performed three experimental trials in a randomized order: 1) RE (8 ϫ 5 leg press repetitions at 80% 1-repetition maximum) performed alone and RE preceded by either 2) HIT cycling [10 ϫ 2 min at 120% lactate threshold (LT); HIT ϩ RE] or 3) work-matched MICT cycling (30 min at 80% LT; MICT ϩ RE). Vastus lateralis muscle biopsies were obtained immediately before RE, either without (REST) or with (POST) preceding endurance exercise and ϩ1 h (RE ϩ 1 h) and ϩ3 h (RE ϩ 3 h) after RE. Prior HIT and MICT similarly reduced muscle glycogen content and increased ACC Ser79 and p70S6K Thr389 phosphorylation before subsequent RE (i.e., at POST). Compared with MICT, HIT induced greater mTOR Ser2448 and rps6 Ser235/236 phosphorylation at POST. REinduced increases in p70S6K and rps6 phosphorylation were not influenced by prior HIT or MICT; however, mTOR phosphorylation was reduced at RE ϩ 1 h for MICT ϩ RE vs. both HIT ϩ RE and RE. Expression of miR-133a, miR-378, and miR-486 was reduced at RE ϩ 1 h for HIT ϩ RE vs. both MICT ϩ RE and RE. Postexercise mTORC1 signaling following RE is therefore not compromised by prior HIT or MICT, and concurrent exercise incorporating HIT, but not MICT, reduces postexercise expression of miRNAs implicated in skeletal muscle adaptation to RE. concurrent training; interference; exercise intensity; high-intensity interval training; continuous training INCORPORATING BOTH RESISTANCE (RE) and endurance exercise into a periodized training program is termed concurrent training (56). Compared with undertaking RE alone, concurrent training attenuates skeletal muscle hypertrophy and maximal strength development in some (10,19,33,48,53), but not all (5,58,63,75,76), studies. Given that skeletal muscle mass plays an important role in overall metabolic health (87), and many athletes require elements of strength and muscle hypertrophy, concomitantly with a high aerobic capacity (47), minimizing interference during concurrent training has implications for optimizing both health and performance outcomes.