Waldman, HS, Heatherly, AJ, Waddell, AF, Krings, BM, and O'Neal, EK. Five-kilometer time trial reliability of a nonmotorized treadmill and comparison of physiological and perceptual responses vs. a motorized treadmill. J Strength Cond Res 32(5): 1455–1461, 2018—This study examined the reliability of running performance across 3 nonmotorized treadmill (NMT) 5-km time trials (TTs) and physiological, gait, and perceptual differences at a 5-km pace for both NMT and motorized treadmills (MTs). Ten male runners experienced in road racing who had never run on an NMT completed 3 TT to establish personal best 5-km pace. In a later session, participants ran at this pace for 5 minutes on the NMT while metabolic, gait, and perceptual measures were recorded and then ran at outdoor 5-km personal best pace on an MT at 1% grade (counter-balanced crossover design). Intraclass correlation (ICC = 0.95) between the TT1 and TT2 was strong but improved between TT2 and TT3 (ICC = 0.99) with considerable reduction in variability. Nonmotorized treadmill resulted in a 24% slower pace (10.6 ± 1.5 vs. 13.9 ± 2.6 km·h−1; p < 0.001), shorter stride length (1.02 ± 0.10 vs. 1.27 ± 0.18 m; p < 0.001), and decreased cadence (175 ± 12 vs. 181 ± 13 steps per·minute; p = 0.01). However, V[Combining Dot Above]O2, respiratory exchange ratio (RER), lactate concentration, and heart rate did not differ between modalities (NMT = 3.4 ± 0.4 L·min−1, 0.96 ± 0.04, 6.9 ± 3.7 mmol, 172 ± 10 b·min−1; MT = 3.4 ± 0.5 L·min−1, 0.96 ± 0.04, 5.7 ± 3.4 mmol, 170 ± 10 b·min−1). rate of perceived exertion (RPE) for legs, breathing, and overall did not differ between treadmill types. A familiarization session should be included for TT using NMT. Other than gait and pace characteristics similar responses were elicited by both treadmills when running at 5-km pace. However, with these considerations, NMT TT of 4-km might be more appropriate in matching MT 5-km TT duration without altering physiological responses significantly.