Lorenzetti et al. BMC Sports Science, Medicine and Rehabilitation (2018) 10:14 https://doi.org/10.1186/s13102-018-0103-7 RESEARCHARTICLE Open Access How to squat? Effects of various stance widths, foot placement angles and level of experience on knee, hip and trunk motion and loading Silvio Lorenzetti1,2* , Mira Ostermann1,3, Fabian Zeidler1,4, Pia Zimmer1,4, Lina Jentsch1, Renate List1, William R. Taylor1 and Florian Schellenberg1 Abstract Background: Squatting is a core exercise for many purposes. The tissue loading during squatting is crucial for positive adaptation and to avoid injury. This study aimed to evaluate the effect of narrow, hip and wide stance widths, foot position angles (0°, 21°, and 42°), strength exercise experience, and barbell load (0 and 50% body weight, experts only) during squatting. Methods: Novice (N = 21) and experienced (N = 21) squatters performed 9 different variations of squats (3 stance widths, 3 foot placement angles). A 3D motion capture system (100 Hz) and two force plates (2000 Hz) were used to record mediolateral knee displacement (ΔD*), range of motion (RoM) at the hip and knee joints, and joint moments at the hip, knee, and lower back. Results: Both stance width and foot placement angles affected the moments at the hip and knee joints in the frontal and sagittal planes. ΔD* varied with stance width, foot placement angles and between the subjects’ level of experience with the squat exercise as follows: increasing foot angle led to an increased foot angle led to an increased ΔD*, while an increased stance width resulted in a decreased ΔD*; novice squatters showed a higher ΔD*, while additional weight triggered a decreased ΔD*. Conclusions: Suitable stance width and foot placement angles should be chosen according to the targeted joint moments. In order to avoid injury, special care should be taken in extreme positions (narrow stand-42° and wide stance-0°) where large knee and hips joint moments were observed. Keywords: Squat exercise, Squatting, Knee alignment, Varus / valugus Background displacement of the knee [3]. Common techniques to Exercises related to movements from daily activities are vary the squat exercise include changes in stance width, of major interest within physical exercise development foot placement angle, hip depth, and extra load. Similar and research. Squatting features components of everyday to split squats [4], these different techniques lead to functional movements such as walking, ascending and different loading conditions and movements and thus to descending stairs, sitting down, and standing up [1, 2]. different opinions among therapists, coaches, and ex- The squat strengthens the muscles in the lower limb perts regarding the most effective squatting execution. and improves the ability to counteract a medial or lateral Besides the health benefits, and a general low injury risk of strength training compared to other sports, squatting * Correspondence: [email protected] has been identified as a strength exercise with a raised 1Institute for Biomechanics, ETH Zurich, Leopold-Ruzicka-Weg 4, 8093 Zürich, Switzerland risk of injury for the lower limbs and the trunk com- 2Swiss Federal Institute of Sport Magglingen, SFISM, Hauptstrasse 247, 2532 pared to other strength exercises [5]. Evidence based Magglingen, Switzerland guidelines exist for the execution of a squat, and these Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Lorenzetti et al. BMC Sports Science, Medicine and Rehabilitation (2018) 10:14 Page 2 of 11 include foot stance of shoulder width or wider, maintain- activity may cause excessive mediolateral knee displace- ing the feet flat on the ground, and toes pointing ments, and squatting variations such as heel lifts or forward or slightly outward by no more than 10° [6–8]. improved strength in the ankle lead to lower mediolat- In addition, the knees should track over the toes eral movements [22–25]. throughout the squat motion without knee displacement While anterior-posterior translation of the knee during either medially or laterally [7]. To create and evaluate squats or deep knee bends has been studied [9, 10, 26, 27], these guidelines, a number of studies have investigated the mediolateral displacement (leading to varus or valgus the kinematics, muscle activity, and loading conditions postures) has only been examined using cohorts with that occur in the lower extremities during different excessive medial knee displacement, showing that increas- execution forms of the squat exercise. A comparison ing knee valgus angles result in an increasing risk factor between the restricted knee (where the knee should not for injury. To lower mediolateral movements, changes in pass anteriorly of the toe) and the unrestricted knee the squatting variations such as heel lifts or improving (where the knee is free to pass beyond the toe) tech- strength in the ankle is recommended [7, 22–25]. How- niques during squatting shows that the range of motion ever, particularly the mediolateral movement of the knee (RoM) of the knee [9, 10] and of the lumbar and thor- within healthy novice and experienced strength exercise acic spine differs significantly and furthermore when participants is missing in literature. Therefore, the aim of adding a greater load [11]. With increasing load, the this study was to assess knee and hip range of motion and RoM of the lumbar curvature decreases significantly, moments, including knee frontal plane displacement, and and the thoracic curvature RoM decreases with in addition spinal curvature, and moment at L4/L5 level, increased additional load on the barbell from 25 to 50% of experienced and novice squatters during different of participant’s body weight [11]. execution forms of parallel back squats. The effect of foot placement angles has primarily been investigated by examining the change in electromyog- Methods raphy muscle activity [12–16] but also by kinematic and Participants kinetic analyses. While stance width affects muscle activ- Forty-two participants were recruited by email and pub- ity in the lower extremities, varying foot placement lic announcement at ETH Zurich and in surrounding angles during squats does not seem to play a major role fitness centres. Novice and experienced participants with on either muscle activity or knee joint contact forces good health, without a lower-limb surgery, and who [17, 18]. In contrast, different stance widths have been regularly exercised in a fitness centre or gym were found to influence the motion and joint loading of hip included. Participants who performed squatting exercises and knee but not the trunk motion [19, 20]. Here, it once a week or more, for at least 1 year, and with a one needs to be mentioned, that these authors included repetition maximum of at least 80% of their body weight powerlifters that probably have acquired a different were considered experienced squatters. All participants squatting strategy than observed in other athletes. provided written informed consent to participate in this Therefore, different types of executions clearly influence study, which was approved by the local ethics committee both musculoskeletal movement and loading conditions; (EK 2015-N-27). The novice group included 11 women thus, specific variations in squat techniques (depth, speed, and 10 men (age 25 ± 6 years; weight 66.3 ± 11.2 kg; stance width, and bar load) can be optimally tailored to height 172.2 ± 8.8 cm) and the experienced group achieve an athlete’sorpatient’s training goals [8, 18]. included 10 women and 11 men (age 25 ± 5 years; While many published studies refer to advanced squat- weight 68.9 ± 11.2 kg; height 174.0 ± 9.1 cm). ters such as Olympic or national weightlifters [15, 19]or powerlifters [20], the present study focusses on un- Squat position derstanding the major influences of squat technique Three stance widths were examined: narrow stance (NS) from a perspective of both more and less experienced described a stance width of 10% of the distance from the participants working out in a gym. No studies have greater trochanter to the floor; hip stance (HS) was a investigated a stance width below 10 cm, since most distance between the two anterior superior iliac spines; attention has been paid to shoulder or hip stance and a wide stance (WS) was twice the distance between width [10, 12, 17, 19, 21]. the anterior superior iliac spines. The HS and WS While it is well known that a greater knee valgus angle equalled the two stance widths analysed by McKean and in the knee during squatting is a risk factor for lower co-workers [21]. Based on previous study results [17], extremity injuries, knee displacement in the frontal three different foot angle placements were examined (0°, plane has only been examined using cohorts with exces- 21°, and 42°). The angle of each foot was defined as that sive medial knee displacement. Here, especially gastro- between the line pointing straight ahead and the foot cnemius muscle tightness and increased adductor axis (line through the middle of the heel and the second Lorenzetti et al. BMC Sports Science, Medicine and Rehabilitation (2018) 10:14 Page 3 of 11 toe). Performing each of the three stance widths with acting on each foot, and the gravitational force of the the three foot placement angles resulted in total nine segments [10, 36].