Research Article Muscle Activation Differs between Three Different Knee Joint-Angle Positions during a Maximal Isometric Back Squat Exercise Paulo Henrique Marchetti, 1,2 Josinaldo Jarbas da Silva, 1 Brad Jon Schoenfeld, 3 Priscyla Silva Monteiro Nardi, 2 Silvio Luis Pecoraro, 1 Julia Maria D’Andréa Greve, 2 and Erin Hartigan 4 1 Graduate Program in Science of Human Movement, College of Health Science (FACIS), Methodist University of Piracicaba, 13423-070 Piracicaba, SP, Brazil 2 Institute of Orthopedics and Traumatology, School of Medicine, University of S˜ ao Paulo, Laboratory of Kinesiology, 05403-000 S˜ ao Paulo, SP, Brazil 3 Department of Health Sciences, Program of Exercise Science, CUNY Lehman College, Bronx, NY 10468, USA 4 Department of Physical Terapy, University of New England, Portland, ME 04103, USA Correspondence should be addressed to Paulo Henrique Marchetti; dr.pmarchetti@gmail.com Received 9 March 2016; Revised 2 June 2016; Accepted 26 June 2016 Academic Editor: Mark Willems Copyright © 2016 Paulo Henrique Marchetti et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te purpose of this study was to compare muscle activation of the lower limb muscles when performing a maximal isometric back squat exercise over three diferent positions. Fifeen young, healthy, resistance-trained men performed an isometric back squat at three knee joint angles (20 ∘ , 90 ∘ , and 140 ∘ ) in a randomized, counterbalanced fashion. Surface electromyography was used to measure muscle activation of the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM). In general, muscle activity was the highest at 90 ∘ for the three quadriceps muscles, yet diferences in muscle activation between knee angles were muscle specifc. Activity of the GM was signifcantly greater at 20 ∘ and 90 ∘ compared to 140 ∘ . Te BF and ST displayed similar activation at all joint angles. In conclusion, knee position alters muscles activation of the quadriceps and gluteus maximus muscles. An isometric back squat at 90 ∘ generates the highest overall muscle activation, yet an isometric back squat at 140 ∘ generates the lowest overall muscle activation of the VL and GM only. 1. Introduction Te squat is one of the most frequently used exercises in the feld of strength and conditioning. Te squat is an exercise that increases hip and knee extensor muscle strength which then indirectly improves the quality of life in athletic and nonathletic populations [1]. Te squat exercise utilizes muscles with diferent morphology (monoarticular and biar- ticular). Muscle forces also vary depending on joint positions (moment arm, length-tension relationship), whether the muscle acts as a prime mover or stabilizer, and whether the task is dynamic or static. Tough evidence suggests that archi- tecture, position, and function drive muscle performance during the squat, little is known about the neuromuscular changes that occur from a muscle activation standpoint. Elucidating how muscle activation patterns change in the monoarticular and biarticular knee and hip extensors during squatting at diferent knee angles would thus enhance our understanding of how one could capitalize on maximizing muscle activation and the best position to specifc evaluations Hindawi Publishing Corporation Journal of Sports Medicine Volume 2016, Article ID 3846123, 6 pages http://dx.doi.org/10.1155/2016/3846123