Vol.:(0123456789) 1 3 Eur J Appl Physiol DOI 10.1007/s00421-016-3524-6 ORIGINAL ARTICLE Slower but not faster unilateral fatiguing knee extensions alter contralateral limb performance without impairment of maximal torque output Olaf Prieske 1  · Saied J. Aboodarda 2  · José A. Benitez Sierra 1  · David G. Behm 3  · Urs Granacher 1   Received: 23 June 2016 / Accepted: 20 December 2016 © Springer-Verlag Berlin Heidelberg 2017 p = .023, d = 2.4). No significant changes were found for EMG data in the non-fatigued leg. Conclusion The present study revealed that both slower and faster velocity fatiguing contractions failed to show any evidence of cross-over fatigue on PIT. However, uni- lateral knee extensor fatigue protocols conducted at slower movement velocities (i.e., 60°/s) appear to modulate torque production on the non-fatigued side (evident in shorter TTP values). Keywords Electromyography · Cross-over fatigue · Isokinetic · Movement velocity · Motor function · Central activation Abbreviations ANOVA Analysis of variance BF m. biceps femoris CON Control condition EMG Electromyographic FAT60 Fatigue protocol at angular velocities of 60°/s FAT240 Fatigue protocol at angular velocities of 240°/s NME Neuromuscular efficiency PIT Peak isokinetic torque TTP Time to peak isokinetic torque VL m. vastus lateralis VM m. vastus medialis Introduction Many training and rehabilitation programs include exer- cises that require prolonged or repetitive unilateral muscle actions (e.g., single leg squats, one arm biceps curls). Thus, unilateral resistance training has been recommended as it incorporates greater core or trunk muscle activation (Behm Abstract Purpose The purpose of the present study was to examine the effects of unilateral fatigue of the knee extensors at dif- ferent movement velocities on neuromuscular performance in the fatigued and non-fatigued leg. Methods Unilateral fatigue of the knee extensors was induced in 11 healthy young men (23.7 ± 3.8 years) at slower (60°/s; FAT60) and faster movement velocities (240°/s; FAT240) using an isokinetic dynamometer. A rest- ing control (CON) condition was included. The fatigue pro- tocols consisted of five sets of 15 maximal concentric knee extensions using the dominant leg. Before and after fatigue, peak isokinetic torque (PIT) and time to PIT (TTP) of the knee extensors as well as electromyographic (EMG) activ- ity of vastus medialis, vastus lateralis, and biceps femoris muscles were assessed at 60 and 240°/s movement veloci- ties in the fatigued and non-fatigued leg. Results In the fatigued leg, significantly greater PIT decrements were observed following FAT60 and FAT240 (11–19%) compared to CON (3–4%, p = .002, d = 2.3). Further, EMG activity increased in vastus lateralis and biceps femoris muscle following FAT240 only (8–28%, 0.018 ≤ p ≤ .024, d = 1.8). In the non-fatigued leg, shorter TTP values were found after the FAT60 protocol (11–15%, * Olaf Prieske prieske@uni-potsdam.de 1 Division of Training and Movement Science, Research Focus Cognition Sciences, University of Potsdam, Am Neuen Palais 10, Building 12, 14469 Potsdam, Germany 2 Faculty of Kinesiology, University of Calgary, Calgary, Canada 3 School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s, NF, Canada