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Knee Joint Kinetics in Relation to Commonly Prescribed Squat Loads and Depths

Cotter, Joshua A.1; Chaudhari, Ajit M.2,3,4; Jamison, Steve T.2,3,4; Devor, Steven T.5,6,7

Journal of Strength & Conditioning Research:
doi: 10.1519/JSC.0b013e3182773319
Original Research
Abstract

Abstract: Cotter, JA, Chaudhari, AM, Jamison, ST, and Devor, ST. Knee joint kinetics in relation to commonly prescribed squat loads and depths. J Strength Cond Res 27(7): 1765–1774, 2013—Controversy exists regarding the safety and performance benefits of performing the squat exercise to depths beyond 90° of knee flexion. Our aim was to compare the net peak external knee flexion moments (pEKFM) experienced over typical ranges of squat loads and depths. Sixteen recreationally trained men (n = 16; age, 22.7 ± 1.1 years; body mass, 85.4 ± 2.1 kg; height, 177.6 ± 0.96 cm; mean ± SEM) with no previous lower-limb surgeries or other orthopedic issues and at least 1 year of consistent resistance training experience while using the squat exercise performed single-repetition squat trials in a random order at squat depths of above parallel, parallel, and below parallel. Less than 1 week before testing, 1RM values were found for each squat depth. Subsequent testing required the subjects to perform squats at the 3 depths with 3 different loads: unloaded, 50% 1RM, and 85% 1RM (9 total trials). Force platform and kinematic data were collected to calculate pEKFM. To assess the differences among loads and depths, a 2-factor (load and depth) repeated measures analysis of variance with significance set at the p < 0.05 level was used. Squat 1RM significantly decreased 13.6% from the above-parallel to the parallel squat and another 3.6% from the parallel to the below-parallel squat (p < 0.05). Net peak external knee flexion moments significantly increased as both squat depth and load were increased (p ≤ 0.02). Slopes of pEKFM were greater from unloaded to 50% 1RM than when progressing from 50% to 85% 1RM (p < 0.001). The results suggest that typical decreases in squat loads used with increasing depths are not enough to offset increases in pEKFM.

Author Information

1Department of Orthopedics, University of California, Irvine, California

2Department of Orthopedics

3Department of Mechanical and Aerospace Engineering

4Sports Health and Performance Institute

5Department of Health and Exercise Science

6Department of Physiology and Cell Biology

7Department of Human Nutrition, Ohio State University, Columbus, Ohio

Address correspondence to Dr. Joshua A. Cotter, jcotter@uci.edu.

Copyright © 2013 by the National Strength & Conditioning Association.