This art icle was downloaded by: [ Near East ern Universit y] On: 07 July 2015, At : 01: 04 Publisher: Rout ledge I nform a Lt d Regist ered in England and Wales Regist ered Num ber: 1072954 Regist ered office: 5 Howick Place, London, SW1P 1WG Journal of Sports Sciences Publicat ion det ails, including inst ruct ions f or aut hors and subscript ion inf ormat ion: ht t p: / / www. t andf online. com/ loi/ rj sp20 Kinematic and EMG activities during front and back squat variations in maximum loads a b c Hasan Ulas Yavuz , Deniz Erdağ , Arif Mit hat Amca & Serdar Arit an c a Sport s Medicine, Near East Universit y Hospit al, Nicosia, Cyprus b School of Physical Educat ion and Sport s, Near East Universit y, Nicosia, Cyprus c Facult y of Sport s Sciences, Hacet t epe Universit y, Ankara, Turkey Published online: 29 Jan 2015. Click for updates To cite this article: Hasan Ulas Yavuz, Deniz Erdağ, Arif Mit hat Amca & Serdar Arit an (2015) Kinemat ic and EMG act ivit ies during f ront and back squat variat ions in maximum loads, Journal of Sport s Sciences, 33: 10, 1058-1066, DOI: 10. 1080/ 02640414. 2014. 984240 To link to this article: ht t p: / / dx. doi. org/ 10. 1080/ 02640414. 2014. 984240 PLEASE SCROLL DOWN FOR ARTI CLE Taylor & Francis m akes every effort t o ensure t he accuracy of all t he inform at ion ( t he “ Cont ent ” ) cont ained in t he publicat ions on our plat form . However, Taylor & Francis, our agent s, and our licensors m ake no represent at ions or warrant ies what soever as t o t he accuracy, com plet eness, or suit abilit y for any purpose of t he Cont ent . Any opinions and views expressed in t his publicat ion are t he opinions and views of t he aut hors, and are not t he views of or endorsed by Taylor & Francis. 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Term s & Condit ions of access and use can be found at ht t p: / / www.t andfonline.com / page/ t erm s- and- condit ions Journal of Sports Sciences, 2015 Vol. 33, No. 10, 1058–1066, http://dx.doi.org/10.1080/02640414.2014.984240 Kinematic and EMG activities during front and back squat variations in maximum loads HASAN ULAS YAVUZ1, DENIZ ERDAĞ2, ARIF MITHAT AMCA3 & SERDAR ARITAN3 1 Sports Medicine, Near East University Hospital, Nicosia, Cyprus, 2School of Physical Education and Sports, Near East University, Nicosia, Cyprus and 3Faculty of Sports Sciences, Hacettepe University, Ankara, Turkey Downloaded by [Near Eastern University] at 01:04 07 July 2015 (Accepted 1 November 2014) Abstract The aim of this study was to compare the musculature activity and kinematics of knee and hip joints during front and back squat with maximal loading. Two-dimensional kinematical data were collected and electromyographic activities of vastus lateralis, vastus medialis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus and erector spinae were measured while participants (n = 12, 21.2 ± 1.9 years old) were completing front and back squat exercises with maximum loading. Paired sample t-test was used for comparisons between two techniques. Results showed that the electromyographic activity of vastus medialis was found to be greater in the front squat compared to the back squat during the ascending phase (P < 0.05, d = 0.62; 95% CI, −15.0/−4.17) and the whole manoeuvre (P < 0.05, d = 0.41; 95% CI, −12.8/−0.43), while semitendinosus (P < 0.05, d = −0.79; 95% CI, 0.62/20.59) electromyographic activity was greater in the back squat during the ascending phase. Compared to the front squat version, back squat exhibited significantly greater trunk lean, with no differences occurring in the knee joint kinematics throughout the movement. Results may suggest that the front squat may be preferred to the back squat for knee extensor development and for preventing possible lumbar injuries during maximum loading. Keywords: strength training, electromyography, biomechanics, two-dimensional, maximal loading Introduction Progressive resistance training is an effective method for developing muscular strength for performance as well as for injury prevention and rehabilitation (American College of Sports Medicine, 1998). Choosing the right exercise is one of the most important factors for achieving the aims of the programme (Fleck, 1999). The squat is a staple multiple joint free weight resistance exercise that develops not only the quadriceps (rectus femoris, vastus lateralis and vastus medialis), but also the hamstrings (biceps femoris and semitendinosus), and it also loads the erector spinae (ES) (McCaw & Melrose, 1999). Increasing the power of these muscles can often translate into improved performance in one or several athletic skills (sprinting, jumping, throwing and striking) (Balshaw & Hunter, 2012; Channell & Barfield, 2008). Due to the popularity of the exercise, many variations have been created by altering the placement of the squat bar: back squat (barbell held across the back slightly above or below the level of the acromion), front squat (barbell held in front of the chest approximately at the level of the clavicles) (Donnelly, Berg, & Fiske, 2006) or overhead squat (barbell held over the head while elbows are fully extended) (Hasegawa, 2004); altering squat depth: partial squats (40° knee angle), half squats (70° to 100°) and deep squats (greater than 100°) (Schoenfeld, 2010); altering stance width: narrow (87–118% shoulder width), medium (121–153% shoulder width) or wide (158–196% shoulder width) (Escamilla, 2000); altering foot rotation: internally or externally rotated feet; or altering squatting surface: stable or labile (power board, BOSU ball, balance cone). However, no standardised measures of quantification have been universally recognised, and terminology can differ between researchers (Schoenfeld, 2010). Two common forms of the squat are the back squat (Figure 1(a)) and the front squat (Figure 1(b)). Competitive or recreational athletes regularly perform the back squat while the front squat is much less common. Although both squats effectively work the lower back, hip and leg muscles, there are slight Correspondence: Hasan Ulas Yavuz, Sports Medicine, Near East University Hospital, Dikmen, Nicosia, 99380 Cyprus. E-mail: ulas.yavuz@neu.edu.tr © 2015 Taylor & Francis Downloaded by [Near Eastern University] at 01:04 07 July 2015 EMG, Kinematic activities of back and front squat 1059 Figure 1. (a) Bar positioning during the back squat. (b) Bar positioning during the front squat. variations in technique and muscular involvement (Gullett, Tillman, Gutierrez, & Chow, 2009). Several studies have described the patterns of the kinematics, kinetics and muscle activities of the knee, hip and ankle during the squat (Dionisio, Almeida, Duarte, & Hirata, 2008; Escamilla, Fleisig, Lowry, Barrentine, & Andrews, 2001; Escamilla et al., 1998; Flanagan, Salem, Wang, Sanker, & Greendale, 2003; Hasegawa, 2004; Isear, Erickson, & Worrel, 1997; McCaw & Melrose, 1999; Stensdotter, Hodges, Mellor, Sundelin, & Hager, 2003; Wretneberg, Feng, & Arborelius, 1996). However, only a few of them have compared front and back squat (Braidot, Brusa, Lestussi, & Parera, 2007; Diggin et al., 2011; Gullett et al., 2009) and even less have studied electromyography (EMG) and kinematics together in the same study to see the interactions (Gullett et al., 2009). Braidot et al. (2007) compared the kinematics, dynamics, the power and the energy in the different joints during the complete cycle from the exercise in the different variants of squat. A better development of energy with the front bar is observed in the knee, allowing a better muscular exercise with the same load. In the study of Diggin et al. (2011), back squat exhibited a significantly greater trunk lean than the front squat (P < 0.05), with no differences in the knee joint kinematics. However, these studies did not quantify the electromyographic data and muscle activity during the front and back squat. Furthermore, the load to evaluate the exercise is calculated on the basis of 50% of one repetition maximum (1RM) for both variants. Gullett et al. (2009) reported that the front squat was as effective as the back squat in terms of overall muscle recruitment, with 70% of 1RM load for each squat technique. Heavy loading in experienced individuals is needed to recruit the high-threshold motor units that may not be activated during light-tomoderate lifting (Kraemer & Ratamess, 2004). Besides, during lower loading conditions, stronger muscles may compensate the activation of weaker ones and cause personal varieties. But during maximal loading, all related muscles must be fully activated in order to complete the manoeuvre. That will form a normalisation in terms of muscle activity and naturally EMG signalling. Clark, Lambert, and Hunter (2012) emphasised that the sub-maximal load used in Gullet’s study might have failed to elicit the possible difference between back and front squat. Furthermore, an increase in trunk forward lean was shown with higher loads by Hay, Andrews, Vaughan, and Ueya (1983) and Kellis, Arambatzi, and Papadopoulos (2005) during squat. Therefore obviously, squat kinematics and EMG signalisation pattern can change with maximal loading. We aimed to compare the musculature activity and kinematics of knee and hip joints during front and back squat with maximal loading and investigate the possible differences in these two common squat variations. Methods Participants Twelve healthy male individuals, who were experienced at performing front and back squats, participated in this study. All participants were righthanded and had no history of orthopaedic injury 1060 H.U. Yavuz et al. or surgery that would have limited their ability to perform the squatting techniques. Before participation, informed consent was obtained from each participant. The investigation was conducted according to the Declaration of Helsinki and approved by the Near East University Scientific Researches, Evaluation and Ethic Commission (YDÜ/2012/11–60). Downloaded by [Near Eastern University] at 01:04 07 July 2015 Instrumentation An eight-channel dual-mode portable EMG and physiological signal data acquisition system (Myomonitor IV, Delsys Inc., Boston, MA, USA) was used for data collection. Data collections were conducted using EMG Works Acquisition 4.0.5 (Delsys Inc.). The amplifier bandwidth frequency ranged from 20 to 450 Hz, with an input voltage of 9 VDC at 0.7 A and the common-mode rejection ratio was 80 dB. Data were recorded at a sampling rate of 1000 Hz over a wireless local area network to the host computer for real-time display and storage. Seven channels of this system were used to assess the EMG activity of vastus lateralis, vastus medialis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus and ES. Recording sites were prepared by shaving the area and wiping with alcohol pads to decrease electrical impedance. Electrodes (41 × 20 × 5 mm, DE-2.3, Delsys Inc.) were placed along the longitudinal axis of each muscle tested on the right side (dominant side) of the participant’s body according to the procedures from Gullett et al. (2009) (Table I). The sensor contacts are made from 99.9% pure silver bars measuring 10 mm in length, 1 mm in diameter and spaced 10 mm apart from optimal signal detection and consistency. A 5.08 cm diameter oval-shaped common reference electrode (Dermatrode HE-R, American Imex., Irvine, CA, USA) was placed on the iliac crest of the right leg. At the same time, the EMG system was synchronised with a Samsung (VP-D375 W) video camera with a shutter speed of 1/250 s by using National Instruments USB-6501 Digital I/O trigger box (Delsys Inc.). Video recordings were made with AMCap (Microsoft, V 3.0.9) video capture software. For kinematical data, reflective markers (3 cm diameter) were attached and positioned over the following bony landmarks: (a) lateral malleolus of the right foot, (b) upper edges of the lateral tibial plateau of the right knee, (c) posterior aspect of the greater trochanters of the right femur and (d) end of the right side of the Olympic bar. A calibration plane that consists of eight control points was used for twodimensional spatial reconstruction. A standard 20.5-kg Olympic barbell, discs (Werksan, Ankara, Turkey) and a continental squat rack were used during the squat. Procedures The participants were required to attend two sessions. A pretest was given to each participant 1 week before the actual testing session. The experimental protocol was reviewed, and the participants were given the opportunity to ask questions. During the pretest, the participant’s RM was determined and recorded for the back squat and front squat. The procedure used for assessing 1RM was described by Kraemer and Fry (1995). The participants were asked to perform initial preparation on a stationary bike for 3–5 min at the beginning of the pretest session and then performed a warm-up set of 8–10 repetitions at a light weight (approximately 50% of assumed 1RM). A second initial preparation consisting of a set of three to five repetitions with moderate weight (approximately 75% of 1RM) and a third initial preparation including one to three repetitions with a heavy weight (approximately 90% of 1RM) followed. After the initial preparation, the participants performed 1RM strength exercises by enhancing the load during consecutive trials until the participants were unable to properly perform a proper lift, complete Table I. A description of the positioning of each electrode in relation to the muscle being tested developed by Broer and Houtz (1967) and described by Gullett et al. (2009). Muscle Rectus femoris Vastus lateralis Vastus medialis Erector spinae Gluteus maximus Electrode placement Approximately midway between the anterior inferior iliac spine and the patella on the anterior side of the thigh Approximately two-thirds of the thigh length from the greater trochanter on the lateral side of the thigh Approximately three-fourths of the thigh length from the anterior inferior iliac spine on the medial side of the thigh Three centimetres lateral to the L3 spinous process 50% on the line between the sacral vertebrae and the greater trochanter. This position corresponds with the greatest prominence of the middle of the buttocks well above the visible bulge of the greater trochanter Biceps femoris Midway between the ischial tuberosity and the lateral condyle of the femur on the posterior side of the thigh Semitendinosus Midway between the ischial tuberosity and the medial condyle of the femur on the posterior side of the thigh Reference electrode Iliac crest of the right leg. EMG, Kinematic activities of back and front squat 1061 2001). The descending and ascending motions are much the same as in the back squat (Gullett et al., 2009). Adequate rest was allowed between trials (3– 5 min). Data reduction Downloaded by [Near Eastern University] at 01:04 07 July 2015 Figure 2. Illustrations of measured joint angles during back squat and front squat. (adapted from Starting Strength: Basic Barbell Training, by permission of The Aasgaard Company, Rippetoe & Kilgore, 2007). range of motion and correct technique. Each participant was asked to lower the bar to the point where the knee angle was 90° (Figure 2), which was marked by adjustable stoppers. Adequate rest was allowed between trials (3–5 min). Subsequently, 1 week after the pretest session, the participants performed a second session for data collection. For each participant, all data collection was performed in one day session. After the EMG electrode placement, maximum voluntary isometric contraction (MVIC) data from the quadriceps, hamstrings, erector spine and gluteus maximus were collected according to the procedures described by Konrad (2005). Three 3-s MVIC trials were collected in a randomised manner for each muscle group. Adequate rest was allowed between trials (1 min). All participants performed two to three warm-up sets in preparation for testing. For both lifting variations, each participant used their 1RM weights previously established for the back squat and front squat. Exercise began with a given verbal command. The starting and ending positions for the back squat and front squat were with the knees in full extension, which was defined as 180° knee angle. From the starting position, the participant flexed their knees to minimum knee angle (approximately 90°) and then extended their knees back to the starting position. During the back squat, the barbell positioned across the shoulder on the trapezius, slightly above the posterior aspect of the deltoids, and the hips and knees flexed until the thighs are parallel to the floor (Baechle and Earle, 2000; Delavier, 2001). Then, the participant extended the hips and knees until the starting position is reached, keeping the back flat, the heels on the floor and the knees aligned over the feet (Baechle and Earle, 2000; Delavier, 2001). During the front squat, the barbell positioned across the anterior deltoids and clavicles and the elbows fully flexed to position the upper arms parallel to the floor (Baechle and Earle, 2000; Delavier, The sampling of EMG and video recordings were initiated simultaneously with the beginning of the first squat repetition. For synchronisation, a LED connected to the trigger box (National Instruments USB-6501 Digital I/O) outputted a digital signal when the Myomonitor started data acquisition. With the data acquisition, the LED lit and it went off as the data stopped. The data obtained from this procedure were used to specify the start of the required portion and the length of the requested portion. Kinematical data were analysed by using the saSuite two-dimensional kinematical analysis programme which was developed by Hacettepe University, Faculty of Sports Sciences, Biomechanics Research Group, Ankara, Turkey. For each trail, the required portion of the video recordings was trimmed, the anthropometric points were digitised and the two-dimensional positional data were obtained. The raw position data of the joints were smoothed using a moving average filter, and the angular kinematics of the knee and hip joints were calculated. All EMG data were partitioned into ascending and descending phases. Movement time was normalised into 10 movement phases to control inter-individual differences. Knee and hip angle changes were examined throughout the descending and ascending phases. EMG data were analysed according to the procedures from International Society of Electrophysiology and Kinesiology (Merletti, 1999) by using the EMG Works Analysis 4.0 (Delsys Inc. Boston). To calculate the mean normalised EMG values, the raw EMG signals were subsetted, filtered (Passband: 3, Response: Bandpass, Corner F1: 10 Hz, Corner F2: 500 Hz), rectified, integrated (root mean square (Window Length: 0.100, Window Overlap: 0.08, Remove Ofset.)) and normalised to the participants highest corresponding MVIC trial. Statistical analysis Kinematic and electromyographic data were analysed and compared between the front and back squad by using paired sample t-tests (P < 0.05). Throughout the text, data for all participants performing each type of exercise were averaged and presented as means, standard deviations, P-value, effect size (Cohen’s d; Cohen, 1988) and 95% 1062 H.U. Yavuz et al. confidence intervals. Cohen’s categories were used to evaluate the magnitude of these sizes (small if 0 ≤ [d] ≤ 0.5; medium if 0.5 ≤ [d] ≤ 0.8 and large if [d] > 0.8) (Cohen, 1988). d = 0.41; 95% CI, −12.8/−.43). There were no other differences in any other muscles. Normalised average EMG values as a %MVIC, Pvalues, effect size (Cohen’s d; Cohen, 1988) and 95% confidence intervals between descending and ascending phases, performed with 1RM loads, between back and front squats are shown in Table III. EMG activities of gluteus maximus (P < 0.05, d = 0.78; 95% CI, −25.81/−11.20), biceps femoris (P < 0.05, d = 0.97; 95% CI, −19.74/−12.60) and semitendinosus (P < 0.05, d = 1.05; 95% CI, −20.72/−7.28) during back squat and EMG activities of gluteus maximus (P < 0.05, d = 0.62; 95% CI, −22.09/−11.18), biceps femoris (P < 0.05, d = 0.38; 95% CI, −14.86/−4.71) and semitendinosus (P < 0.05, d = 0.48; 95% CI, −8.40/−.34) during front squat were found to be significantly higher. EMG activity of the vastus medialis (P < 0.05, d = 0.32; 95% CI, −11.03/−.53) during the ascending phase was higher only. The mean EMG activities as a percentage of maximal voluntary isometric contraction (% MVIC), P-values, effect size (Cohen’s d; Cohen, 1988) and Downloaded by [Near Eastern University] at 01:04 07 July 2015 Results The mean 1RM loads that were employed during testing were 109.17 ± 25.51 kg for the back squat and 85.00 ± 15.67 kg for the front squat. This was 138.83 ± 32.62% of their body weight for back squat and 105.87 ± 24.34 for front squat. Participants could lift significantly higher loads with back squat comparing to the front squat (P < 0.05, d = −1.28; 95% CI, 16.28/32.04). Normalised EMG values as a percentage of maximal voluntary isometric contraction (% MVIC), P-values, effect size (Cohen’s d; Cohen, 1988) and 95% confidence intervals between back and front squats are shown in Table II. Vastus medialis EMG activity was found to be greater during the front squat compared to back squat (P < 0.05, Table II. Mean EMG activities as a percentage of maximal voluntary isometric contraction (% MVIC), P-values, effect size (Cohen’s d; Cohen, 1988) and 95% confidence intervals for the back squats and front squats throughout entire movements, performed with 1RM loads. 95% CI Muscle Back squat (mean ± s) Rectus femoris Vastus medialis Vastus lateralis Erector spinae Gluteus maximus Biceps femoris Semitendinosus 36.7 48.8 47.0 43.2 37.1 26.2 21.5 ± ± ± ± ± ± ± Front squat (mean ±s) 12.4 13.9 15.1 15.6 23.5 16.1 11.7 46.1 55.4 51.2 46.2 37.2 24.1 16.0 ± ± ± ± ± ± ± 21.7 18.0* 17.3 12.1 27.0 25.4 8.7 P d L U 0.118 0.038* 0.149 0.495 0.959 0.611 0.115 0.53 0.41 0.26 0.22 0 −0 −0.53 −21.7 −12.8 −10.2 −12.5 −5.5 −6.5 −1.6 2.82 −0.43 −1.75 0.49 5.23 10.6 12.6 Note: *Significantly higher EMG activities during the front squat compared to the back squat (P < 0.05). Table III. Back squats and front squats mean EMG activities as a percentage of maximal voluntary isometric contraction (% MVIC), P-values, effect size (Cohen’s d; Cohen, 1988) and 95% confidence intervals between descending and ascending phases, performed with 1RM loads. Back squat Muscle Descending phase (mean ±s) Rectus femoris Vastus medialis Vastus lateralis Erector spinae Gluteus maximus Biceps femoris Semitendinosus 37.9 48.3 45.9 41.1 28.8 18.7 15.0 ± ± ± ± ± ± ± 12.1 14.3 13.9 14.0 18.9 14.9 6.9 Ascending phase (mean ± s) 36.0 49.3 48.5 46.0 47.3 34.9 29.0 ± ± ± ± ± ± ± 13.8 13.9 17.2 17.6 27.7* 18.2* 16.2* Front squat 95% CI P d L U Descending phase (mean ± s) 0.455 −0.15 −3.562 −7.432 46.4 ± 0.617 0.07 −5.293 3.286 53.1 ± 0.223 0.17 −7.005 1.821 48.0 ± 0.124 0.31 −11.286 1.564 45.1 ± 0.000* 0.78 −25.810 −11.200 30.0 ± 0.000* 0.97 −19.740 −12.600 19.7 ± 0.001* 1.05 −20.720 −7.280 14.0 ± 24.4 19.3 15.8 12.0 23.0 23.3 8.1 Ascending phase (mean ± s) 46.7 58.9 56.2 48.1 46.6 29.5 18.4 ± ± ± ± ± ± ± 19.4 17.1* 22.2 16.8 30.1* 28.7* 10.1* 95% CI P d 0.922 0.33* 0.68 0.451 0.000* 0.001* 0.036* 0.01 0.32 0.43 0.20 0.62 0.38 0.48 Note: * Significantly higher EMG activities during the ascending phase compared to the descending phase (P < 0.05). L U −7.122 6.500 −11.036 −.533 −17.190 0.7269 −11.276 5.367 −22.098 −11.188 −14.864 −4.711 −8.404 −0.343 EMG, Kinematic activities of back and front squat 1063 Table IV. Mean EMG activities as a percentage of maximal voluntary isometric contraction (% MVIC), P-values, effect size (Cohen’s d; Cohen, 1988) and 95% confidence intervals between back squats and front squats during the descending and ascending phases, performed with 1RM loads. Descending phase Ascending phase 95% CI Muscle Back squat Front squat (mean ± s) (mean ± s) Rectus femoris Vastus medialis Vastus lateralis Erector spinae Gluteus maximus Biceps femoris Semitendinosus 37.9 48.3 45.9 41.1 28.8 18.7 15.0 ± ± ± ± ± ± ± 12.1 14.3 13.9 14.0 18.9 14.9 6.9 46.4 53.1 48.0 45.1 30.0 19.7 14.0 ± ± ± ± ± ± ± 24.4 19.3 15.8 12.0 23.0 23.3 8.1 P d L 95% CI U Back squat (mean ± s) 0.200 0.44 −22.011 5.164 36.0 ± 13.8 0.204 0.28 −12.627 3.020 49.3 ± 13.9 0.396 0.14 −7.088 3.028 48.5 ± 17.2 0.438 0.31 −14.953 6.940 46.0 ± 17.6 0.573 0.06 −5.460 3.181 47.3 ± 27.7 0.765 0.05 −7.883 5.959 34.9 ± 18.2 0.676 −0.13 −4.052 6.019 29.0 ± 16.2** Front squat (mean ± s) 46.7 58.9 56.2 48.1 46.6 29.5 18.4 ± ± ± ± ± ± ± 19.4 17.1* 22.2 16.8 30.1 28.7 10.1 P d 0.061 0.64 0.002* 0.62 0.096 0.39 0.665 0.12 0.841 −0.02 0.329 −0.22 0.039** −0.79 L U −21.917 0.578 −15.001 −4.177 −16.932 1.590 −12.493 8.292 −7.001 8.447 −6.257 17.099 0.624 20.595 Downloaded by [Near Eastern University] at 01:04 07 July 2015 Notes: * Significantly higher EMG activities during the front squat compared to the back squat (P < 0.05); **Significantly higher EMG activities during the back squat compared to the front squat (P < 0.05). Figure 3. Minimum hip angles reached during the back squat (BS) and front squat (FS). * Significant differences (P < 0.05) between the back and front squats. 95% confidence intervals between back squats and front squats during the descending and ascending phases, performed with 1RM loads, are shown in Table IV. There were no significant differences observed between back and front squats during the descending phase. During the ascending phase, the EMG activity of the vastus medialis was found to be significantly higher in the front squat compared to the back squat (P < 0.05, d = 0.62; 95% CI, −15.00/−4.17) while the EMG activity of the semitendinosus was higher in the back squat compared to the front squat (P < 0.5, d = −0.79; 95% CI, .62/ 20.59). As can be seen from Figure 3, significant differences were observed between minimum hip angles reached during back squats and front squats. The average minimum hip angle was significantly higher (P < 0.05, d = 1.08; 95% CI, −28.57/−4.28) during the front squat compared to the back squat. Figure 4 shows the mean changes in knee and hip angles throughout the ascending phases of both squatting movements. No difference was observed in knee angles during the whole movement while hip angles were lower in 8 of 10 phases during the back squat compared to front squat, showing an obvious forward trunk lean. According to the angle-specific EMG changes, semitendinosus (P < 0.05, d = −0.23; 95% CI, −2.42/11.11) showed a sudden increase in the sixth phase and biceps femoris (P < 0.05, d = −0.14; 95% CI, −10.93/ 19.11) and gluteus maximus (P < 0.05, d = −0.37; 95% CI, −4.53/30.89) showed a similar but smaller increase in the eighth phase during the back squat compared to the front squat. Discussion Participants could lift significantly greater loads with back squat compared to the front squat (138.8 ± 32.6% of their body weight, 105.9 ± 24.3% of their body weight, respectively) (Figure 1), and this finding is consistent with the previous studies (Gullett et al., 2009; Russell & Phillips, 1989). Instead of the load, the level of effort in voluntary muscle actions determines the degree of motor unit activity (Carpinelli, 2008); consequently, the level of EMG signalling increases. Furthermore, higher loads may increase intradiscal pressure (11), compression on vertebral bodies (10), tibiofemoral (12, 13) and patellofemoral joints (14), which could possibly increase the risk of injury while performing squat. Gullett et al. (2009) emphasised that the muscles tested were equally active during the front squat while lifting less mass, and it seems that the extra load lifted during the back squat is what accounts for the increased tibiofemoral compressive forces and extensor moments observed during these lifts. It is Downloaded by [Near Eastern University] at 01:04 07 July 2015 1064 H.U. Yavuz et al. Figure 4. Knee and hip angle-dependent EMG values of rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), erector spinae (ES), gluteus maximus (GM), biceps femoris (BF) and semitendinosus (ST) throughout the phases of both backs squat (BS) and front squat (FS) movements. * Significant differences (P < 0.05) between back and front squats. very important because excessive tibiofemoral compressive forces could be deleterious to the menisci and articular cartilage (Escamilla, 2000). During the squat, the primary muscles acting around the knee are the quadriceps femoris (vastus lateralis, vastus medialis, vastus intermedius and rectus femoris), which carry out concentric knee extension, as well as eccentrically resisting knee flexion. For both back and front squats, vastus medialis and vastus lateralis produced more activity than the rectus femoris during the whole manoeuvre which is in agreement with the data from Escamilla et al. (1997, 1998), Escamilla (2000), Escamilla et al. (2000), Hwang, Kim, and Kim (2009), Wretneberg, Feng, Lindberg, and Arborelius (1993), Wretneberg et al. (1996) and Isear et al. (1997). Schoenfeld (2010) reported that this may be logical because the rectus femoris is both a hip flexor and knee extensor and thus shortens at one end while lengthening at the other during the squat, with little if any net change in length throughout movement. Although the loads were heavier during the back squat, mean EMG activities in selected muscles showed no difference with only one exception. Despite the lighter loads during the front squat, vastus medialis mean EMG activity was greater than the back squat during the whole manoeuvres. Gullett et al. (2009) and Stuart, Meglan, Lutz, Growney, and An (1996) reported no differences in muscle activities between front and back squats. The difference in our study can be resulted from the higher loads compared to Gullett et al. (2009) (70% of 1RM) and Stuart et al. (1996) (50 pounds), which may recruit more motor units during the movements. When we divided the manoeuvres into ascending and descending phases, all muscles tested were more active during the ascending phase than during the descending phase. These findings are in accordance with those of several other studies (Escamilla et al., 1998; Escamilla et al., 2000; Gullett et al., 2009; McCaw & Melrose, 1999; Stuart et al., 1996). EMG activities were higher during the ascending phase compared to the descending phase for all muscles during both the front and the back squat. But statistically significant differences were seen for gluteus maximus, semitendinosus and biceps femoris during both the front and the back squat and for vastus medialis during the front squat. We observed no significant EMG activity differences between the back and front squats during the descending phases. However, during the ascending phase EMG activity of the vastus medialis was higher in the front squat compared to the back squat while EMG activity of the semitendinosus was higher in the back squat compared to the front squat. The front squat is believed to be a more isolated manoeuvre for quadriceps (Grahammer, 1986; Hatfield, 1983), and this result may support this idea. The heavier external resistance and more inclined torso during the back squat create a larger resistance moment, which requires greater muscular effort to counterbalance (Swinton, Aspe, & Keogh, 2012). It was shown that increased forward trunk lean causes an increase in hamstring activity (Escamilla et al., 2000; Gullett et al., 2009; Scotten, 2010). This may explain the higher semitendinosus EMG activity during the ascending phase of the back squats. When we divided the manoeuvres into 10 phases for being able to compare the movement patterns, Downloaded by [Near Eastern University] at 01:04 07 July 2015 EMG, Kinematic activities of back and front squat we did not observe any significant difference in knee angles between the back and front squats. However, we observed significantly lower hip angles in 8 of 10 phases during the back squat. The lowest hip angles reached during the manoeuvres were significantly lower in the back squat compared to the front squat. These findings showed an increased forward lean during the back squat compared to the front squat during maximum loading. When we check angle-specific EMG changes for each muscle, we saw that EMG activity patterns were quite parallel to each other for most of the muscles in both squat variants. Semitendinosus EMG activity showed a sudden increase in the sixth phase, which also shows the lowest hip angle and the starting of the ascending phase. Gluteus maximus and biceps femoris showed a similar but weaker change in pattern during the middle of the ascending phase (eighth phase). This may probably be due to the extra effort of the hip extensors to maintain the balance by compensating the increased forward lean during back squat. In both the squatting techniques, as the performers lower throughout the eccentric phase they are required to lean forward in order to maintain balance. Centre of gravity moves further away from the lumbar spine, increasing the moment arm and torque. As a result, the shear forces occurring within the lumbar spine would also increase (Comfort & Kasim, 2007; Diggin et al., 2011; Gullett et al., 2009). Increased forward lean reduces tolerance to compressive load and results in a transfer of the load from muscles to passive tissues, heightening the risk of disc herniation (Matsumoto et al., 2001). As previously stated, such an increase in shear force, under regular high loading conditions (e.g. 1RM), may predispose an athlete to injury if these forces continually exceed the strain capabilities of the joint connective tissues (Comfort & Kasim, 2007). That is why, it is beneficial to maintain a posture that is as close to upright as possible at all times for preventing the lumbar injuries (Schoenfeld, 2010). Conclusion We studied the musculature activity and kinematics of knee and hip joints during front and back squats with maximum loading (1RM). The front squat was shown to be just as effective as the back squat under maximum loading conditions in terms of overall muscle activity, with no difference in knee joint kinematics and significantly less forward lean in hip joint, which may probably show less lumbar injury risk. We also managed to show that the front squat created higher EMG activity in vastus medialis despite the lighter loads compared to back squat that agrees 1065 with the idea of “being a more isolated movement for knee extensors.” It is a known fact that the back squat is used much more commonly compared to its front variation. Results may suggest that the front squat may be a better choice for focusing on knee extensor improvement and/or for preventing lumbar injuries under maximum loading conditions. References American College of Sports Medicine. (1998). 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