A Biomechanical Comparison of the Deadlift Versus the Squat

Read Coach Koel's senior comprehensive paper for Occidental College. This paper was vetted by multiple PhD researchers and the entirety of the Kinesiology department of Occidental College.

Abstract

The purpose of this paper is to examine the biomechanics of the barbell back squat and deadlift and their roles as foundational exercises that build both muscular and kinematic control. The squat and deadlift are both complex multi-joint movements that can be performed with variations in depth, magnitude of load, velocity, foot placement, position of load, or equipment in order to customize the exercise to the goals of the lifter. However, this paper will only analyze the narrow stance barbell back squat and straight and hexagonal bar deadlift when executed with proper form. The musculature and neurological control used to stabilize and maintain correct posture while completing the lifts are similar in nature to those exercised for portions of many other movements across various sports. The motor patterns used in these two lifts are similar to kinematic patterns used in sports like football, soccer, track, or any sport that requires acceleration or deceleration.  The eccentric phase of the squat is especially similar to braking mechanics when running or absorbing the impact from any jump or fall. The concentric phase of the deadlift and squat is also similar to the kinetics of jumping, which is essential in many sports, such as basketball. The deadlift and squat are also often considered good indicators of anaerobic lower body force production, a vital component of sprinting, as well as many sports.

A Biomechanical Comparison of the Deadlift Versus the Squat and Their Prescription in Resistance Exercise Regimens

To best achieve specific performance goals an athlete must optimize his or her training regimen. It is critical for success to perform only the exercises that will efficiently induce the most beneficial adaptations in order to narrow down one’s workload to a manageable amount, and avoid overtraining. Furthermore, variations exist of every exercise, so to maximize the efficiency of a training program, only the most beneficial variation of each exercise should be performed to match the needs of the individual (Hamlyn, Behm & Young, 2007). Resistance exercise is one of the most popular and effective forms of training for many athletes, as well as for non-athletes, who can also garner many health benefits that will impact their lives on a daily basis.

The squat and deadlift are two of the most frequently used exercises in the field of strength and conditioning because they require the recruitment of a large amount of musculature when compared with most other exercises, they are ground based (closed kinetic chain exercises), and are multi joint movements so the overload is distributed across many muscles (Bishop, DeBeliso, Sevene & Adams, 2014). In addition, these movements bear a high similarity to many sport actions (such as jumping, sprinting, and braking) and their difficulty is easily adjustable through varying the load on the barbell. The complexity of these movements and the multitude of variables that determine performance make understanding their biomechanics essential for reducing the risk of injury and optimizing the benefits received when performing the exercise. They both activate very similar muscle groups to accomplish a similar function, primarily ankle plantarflexion, and knee and hip extension, but they differ from each other in how the external load is imposed on the lifter (Zink, Perry, Robertson, Roach & Signorile, 2006). This paper will analyze the differences in biomechanical stresses imposed on the body when performing a squat versus a deadlift, as well as how these unique stresses affect prescription of either exercise as part of a training regimen. When performing a squat the external load is imposed from above the lifter via a barbell resting on the traps and lower neck, as opposed to a deadlift where the load is below the lifter, forcing them to grip it with their hands in order to successfully load and perform the movement. This key difference in imposition of load affects primarily core and trunk stability requirements, as well as possibly affecting the performance of the eccentric phase and transition between phases as the lifter may choose to use the ground to decelerate the load. The deadlift is also commonly performed in two distinct ways, with a conventional straight barbell, or a hexagonal barbell that allows the lifter to stand within its frame, which will affect how the external load is applied. An analysis of both techniques will further the understanding of how to apply and prescribe the movement in resistance training regimens. The squat and deadlift movements are both particularly important because they have been proven to increase the rate of torque development and vertical jump performance in novices (Requena et al., 2011; Thompson et al., 2015). In addition, when performed with proper form, these movements have a very low incidence of injury and require the innervation of a very high percentage of the body’s musculature (Lynn & Noffal, 2012; McGuigan & Wilson, 1996; Schoenfeld, 2010; Swinton, Lloyd, Keogh, Agouris & Stewart, 2012).

The narrow stance barbell back squat movement begins with the lifter in an upright position, with the knees and hips fully extended, both feet flat on the ground and directly underneath the lifter’s hips, and a near vertical chest angle. The exercise starts with the eccentric phase, which is characterized by hip and knee flexion, and ankle dorsi-flexion. The lifter moves the hips posteriorly as they squat down, displacing the center of mass anteriorly (Swinton et al., 2012; Whitting, Meir, Crowley-Mchattan & Holding, 2015). The concentric phase of the squat is initiated when the lifter’s femurs are parallel with the ground, coinciding with slightly more than ninety degrees of flexion at the knee. This portion of the movement is characterized by extension at the hip and knee joints, as well as plantarflexion of the ankle joint.

Research conducted by Bezerra et al. (2013) states that the deadlift is commonly prescribed by strength and conditioning coaches as part of a resistance training program to strengthen the legs, hips, back, and torso musculature. Traditional deadlift begins with the knees flexed in a squat type position, with the elbows extended and an alternate grip used to hold the bar, generally biacromial breadth (shoulder width) apart. The bar is held positioned over the metatarsal region of the lifter’s feet, then during the concentric portion of the exercise it is raised from the floor to a mid-thigh position by extending the hip and knee joints. Stance width can change between movement variations but proper form for this paper will be defined as hip width, having the feet directly underneath the hips. The lifter begins the exercise with a near 90 degree knee angle with the thigh parallel to the ground. The hips are flexed with the torso almost 45 degrees from vertical with the scapulae partially abducted. In the concentric phase of the lift the bar is raised above the shins while the hips and knees simultaneously and evenly extend. The trunk is raised to an upright position while the scapulae are adducted, with the completion of the concentric phase being marked by the lifter achieving a fully upright standing position (Swinton et al., 2011b). The eccentric phase of this lift is performed by lowering the bar to the ground with all joint movements performed in reverse order.

The anatomical positioning of proper squatting form is very similar to that required by proper deadlifting form, both of which are essential to minimize risk and maximize benefit. Proper form is defined as maintaining a stable upright body position with a rigid spine, eliminating any non-sagittal plane motion throughout both the eccentric and concentric phases of the movement (Swinton et al., 2012). A natural vertebral alignment must be sustained throughout the lift in order to minimize the risk of injury, with the cervical and lumbar vertebrae in a lordotic curve, while the thoracic vertebrae remain in a kyphotic curve (Swinton et al., 2012; Whitting et al., 2015). It is worth noting however, that the absolute angle of the spine in relation to the pelvis will usually increase as the lifter descends into hip flexion, exposing the vertebral column and its accompanying musculature to high internal forces (Flanagan, Kulik & Salem, 2015; Swinton et al., 2012). Bar placement and grip may vary depending on preference or technique but it is usually recommended to have the center of the barbell rest on the C7 vertebra evenly between the trapezius on both sides and to grab the rough part of most barbells, lateral to the shoulder.

Understanding each of the major joint complexes involved in the squat and deadlift is imperative to reduce discrepancies in form and maximize performance. Emphasis will be placed on certain aspects of each complex that are deemed the most pertinent, beginning with the strongest contributor to torque production: the hip. Torque about the hip increases in concurrence with greater degrees of hip flexion throughout the squat, with maximum torque observed near the transition between the eccentric and concentric phases of the exercise (Swinton et al., 2012). Hip mobility is crucial for safe and effective squatting technique because a reduced range of motion can lead to the lifter leaning forward to compensate, increasing shear stress on the spine. In addition, using posterior pelvic movement as a compensatory mechanism to increase hip flexion can result in increased lumbar stress (Swinton et al., 2012).

A study conducted by Bezerra et al. (2013) found that the vastus lateralis exhibited peak electromyography (EMG) activity during the concentric portion of the deadlift in the first 20 degrees of hip extension beginning from full flexion. This is likely observed due to the need for increased extensor torque about the knee during this phase of the movement to counteract the co-contraction of the biceps femoris, which has an increased muscle activity during the same phase as a hip extensor. Some of the hip extensors simultaneously flex the knee as they activate, acting partially as antagonists for the squat and deadlift movements against the knee extensors. If the body is repeatedly presented with these opposing tensions, it will strengthen the surrounding connective tissue over time and ensure stability of the knee. A similar phenomenon also occurs at the hip joint between all the hip extensors and the flexor torque generated by the rectus femoris as it activates to extend the knee, creating another co-contraction that enhances joint stability. (Hales, Johnson, B. & Johnson, J., 2009).  Multiple studies corroborate these findings, as well as that peak biceps femoris activity occurs between 20 and 40 degrees of hip extension from full flexion during both the squat and the deadlift movement.

In order to mitigate the propensity of injury and induce maximum muscle development it is generally recommended to minimize the anterior movement of the knee during the squat, preventing it from passing over the toe. The motive for this particular aspect of squat form is that a shin position close to vertical reduces internal forces at the knee and promotes activation of the hip extensors throughout the lift (Swinton et al., 2012; Whitting et al., 2015). The squat and deadlift are both closed kinetic chain exercises, a characteristic that reduces the strain on the anterior cruciate ligament (ACL) during the movement (Whitting et al., 2015). This is critical when determining the training program for an individual who has injured their ACL, especially considering the current prevalence of such injuries in modern sports.

The ankle complex provides substantial support and assists in power generation throughout the squat. In the upright position prior to descent, the center of pressure (COP) was projected at approximately the mid-foot, with moderate plantar flexor torque. During the acceleration phase, COP shifted toward the heel, while plantar flexion torque decreased. During the deceleration phase the COP was displaced to the toes, resulting in a large increase in plantar flexor torque about the ankle (Swinton et al., 2012). A high degree of mobility at the ankle is required to facilitate balance and control in both the ascent and descent of the squat. When ankle joint flexibility is compromised, there is a tendency for the heels to rise off the floor at greater degrees of dorsiflexion. This can result in compensatory increases in joint moments at the ankle, knees, hips, and spine, potentially causing injury particularly if the lifter is squatting with a large external load. If an athlete exhibits reduced range of motion at the ankle joint, which can sometimes be accredited to tightness of the soleus, they may have a predisposition to medial knee displacement that causes increased knee valgus angulation and therefore a corresponding increase in stress on the ACL (Swinton et al., 2012).

A vast amount of musculature contributes to the isometric contraction performed about the vertebral column during the squat and deadlift but the greatest contributors to spinal stabilization are the lumbar erector spinae as they assist in the resistance of vertebral shear stress, in addition to helping with maintenance of anteroposterior spinal integrity. Keeping a neutral spine throughout the movement is vital to the safety of the lifter as excessive amounts of flexion or extension transfer the load from the muscles to surrounding connective tissue. This can greatly increase the risk of incurring injuries, including disk herniation, and a variety of problems suffered from a disproportionate compressive load on the lumbar vertebrae (Swinton et al., 2012). Many muscles are also recruited as stabilizers to counteract small irregularities that occur throughout the squatting movement, most of which perform isometric contractions, such as the abdominals, erector spinae, trapezius, and rhomboids in order to facilitate postural steadiness of the trunk (Whitting et al., 2015). Overall, approximately just over 200 muscles are activated throughout the extent of the squat (Swinton et al., 2012).

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Overall, high intensity weighted multi-joint movements can be generally assumed to require more core and trunk muscle stability activation than unstable surface or less weighted exercises. The use of free weights incorporates a degree of instability into the movement despite being performed on a stable surface because of the force vectors. The load isn’t perfectly imposed onto a vertical body, while the spine may be at a near vertical angle, a rotary torque is produced about the torso from the bar resting on the trapezius muscles, attempting to crush the lifter who must create internal pressure and contract much of their trunk musculature to counter this effect (Hamlyn et al., 2007). Hamlyn et al. (2007) found that mean EMG activity in the lumbo-sacral erector spinae (LSES) muscles during the performance of dynamic, weightlifting, and isometric instability exercises was significantly greater during the performance of the Olympic bar squat loaded at 80% of 1 rep maximum (1RM) than any other exercise, as shown in Figure 1. It was found that erector spine muscles in the lumbosacral region showed an increase of 34.5% in EMG activity during a squat when compared to a deadlift, although it was recognized that individual technique likely plays a large role in stabilizer muscle activation because of the high variations present in the EMG data. The LSES assists with handling compressive forces along with other local stability muscles of the spine that have a role in the maintenance of segmental stability but can be insufficient without the help of large global muscles during specific movements, such as the squat. The gluteus maximus is one such global muscle with high activity to assist with stabilization, balance, and generating forces to control the range of motion (Hamlyn et al., 2007). It was hypothesized that the greater EMG activity measured was due to the lifters attempting to counterbalance their body and the resistance during the movement. During this lift the body is comparable to an inverted pendulum, producing a susceptibility for the center of gravity to oscillate. Limiting the amount of instability preserves balance throughout the movement. If a load is imposed above the center of gravity, as it is with the squat exercise, it can generate torques that contribute to instability (Hamlyn et al., 2007). Furthermore, they found that the squat and deadlift loaded at 80% of 1RM elicited more paraspinal muscular activity than any other exercises, including various exercises performed on instability devices. This is further substantiated by a study conducted by Chulvi-Medrano et al. (2010) where it was found that performing the squat and deadlift in stable conditions allowed for greater total force production than in unstable conditions. However, it is worth acknowledging that in the study conducted by Hamlyn et al. (2007) the absolute percentage of the maximum voluntary contraction (MVC) is very low, implying that when performing the squat with proper form the LSES will not be heavily recruited. This is due to the fact that the vertebral facets absorb most of the shear stress imposed on the spine during the lift and the LSES is primarily a stabilizer with very low torque production capacity, and therefore is not heavily relied upon to generate paraspinal torque.

Core strength has been emphasized as a valuable component in general, as well as in sports conditioning programs and active rehabilitation programs for persons with low back pain. For individuals under the age of 45 in North America, lower back pain is the most common cause of musculoskeletal issues (Hamlyn et al., 2007). Back disorders often develop as a result of a lack of core strength and endurance in the trunk musculature, which can be remedied via a variety of methods. Deadlifts and squats both require the activation of the aforementioned musculature and when performed consistently as part of a program have been proven to decrease reports of lower back pain, albeit individually depending on the severity of the affliction (Berglund, Aasa, B., Hellqvist, Michaelson & Aasa, U., 2015; Hamlyn et al., 2007).

The deadlift involves dynamically lifting a weight off of the ground, creating a different starting environment for the concentric phase of the movement than the squat. It was found that using a quarter squat position to lift the weight caused the hips to be higher during the initial pull than when in a half squat position, forcing the lifter’s torso to be farther from a vertical angle. The less close to vertical the torso angle, the greater the risk of injury to the spine and back musculature. It is highly recommended to maintain a more upright trunk angle throughout the duration of the lift to put the initial load of the pull onto the quadriceps muscles and less anterior shear stress on the lumbar L4/L5 joint (Bezerra et al., 2013; Schellenberg et al., 2013). There are an infinite number of variations on the deadlift including sumo style, Romanian, and hex-bar. However, the two styles of deadlifting examined in this paper are the traditional and hex-bar deadlift. The hex-bar variant does require specialized equipment instead of a standard barbell, but is likely worth the additional benefit. A study conducted by Camara et al. (2016) suggested that the use of a hexagonal barbell led to different muscle recruitment patterns and may be more effective at developing force, power, and velocity production capacity than deadlifting with a straight bar. They also propose that individuals with lower back pain should use a hex-bar when deadlifting because it can more evenly distribute the load amongst the body’s joints, as well as reducing the torque moment at the lumbar spine. A study conducted by Swinton et al. (2011a) supports these findings and pushes them even further as they found that their participants could lift a heavier 1RM deadlift with a hex-bar than with a straight bar, which suggests that the hex-bar deadlift is an overall superior exercise to the straight bar deadlift.

The squat serves to teach athletes many valuable skills, including inducing flexion or extension evenly in time across joints both concentrically and eccentrically, which minimizes risk of injury. During the squat, the hip and knee, as well as the torso and ankle, flex and extend together with similar magnitudes (Swinton et al., 2012; Whitting et al., 2015). These characteristics are generally present in the performance of the deadlift as well, if sometimes to a lesser degree depending on the form of the lifter. Another such skill is the maintenance of one’s center of mass over their base of support, which is generally good advice for most athletic movements because it allows the athlete to react, change direction, or generate force quickly. It is also advisable to set an athlete’s squat or deadlift stance to the same width as their sport stance to promote similar kinesthia and neurological patterning between the force production desired when squatting and the force production required for sport. This is more pertinent for sports that require stability when lifting a load versus sports that do not involve contact against resistance. Another benefit of the squat is the utilization of the stretch-shorten cycle, which is involved in many sports as athletes often decelerate, mimicking the eccentric phase of the squat, and then subsequently change direction and accelerate, mimicking the concentric phase of the lift. The potential benefit gained from the stretch-shorten cycle, however, must be qualified by the fact that the greater the % of the lifter’s 1RM used during the squat, the slower the movement velocity. Therefore, this decrease in velocity decreases the contribution of the stretch shorten cycle since a greater portion of the stored elastic energy will be dissipated as heat. As expected, there is a greater contribution from the stretch-shorten cycle in a power lift because it is more reliant on speed instead of force production. Performing squats can also serve to improve an athlete’s braking mechanics, because they are generally coached to use a technique that is similar in nature to the eccentric phase of the exercise.

Both the squat and deadlift are widely regarded as two of the most effective exercises for improving strength and athletic performance. They bear similarity to everyday movements, necessitating integration of vertebral muscles for mobilization and stabilization and can induce substantial muscular development in the primary movers when performed properly as part of a resistance training regimen (Ebben et al., 2008; Hales, 2010). Both can specifically translate most effectively to sagittal plane motion as the exercises take place entirely in this plane. 1RM and peak power outputs measured for the traditional squat and deadlift and have been positively statistically correlated with faster sprint times for distances less than 80m (Schoenfeld, 2010; Thompson et al., 2015).

Coaches of any discipline could adapt the training programs they prescribe to induce the adaptations they desire in their athletes. If a coach decided that their athletes were often in situations that specifically required a lot of balance, torso stability, or ability to decelerate heavy loads eccentrically, they may wish to prescribe the squat more often than or instead of the deadlift because it requires those attributes as well. Alternatively, if handling a load eccentrically isn’t important for a certain task but rather only the ability to accelerate a load concentrically and have great grip strength is instead required, then it may be worth prescribing the deadlift more often than or instead of the squat. The programming adjustments made by coaches could essentially mold and adapt their athletes to the customized roles desired. For example, a football defensive lineman must fend off the incoming offensive lineman every play, which is somewhat comparable to handling an eccentric load. Then ideally they press through their opponent into the backfield to disrupt the play, comparable to concentrically overcoming a load. It may also be logical to suggest that torso stabilization is a greatly desired trait for an athlete in this position because their opponent’s technique generally involves punching, pushing, and holding onto any area of the torso, creating a destabilizing torque upon the body. This is comparable to the squat movement more than the deadlift as the external load is imposed in a closer area to the torso and creates destabilizing torques about that area as well.

If a specific type of competition forced athletes into positions similar to those attained during specific training movements, they could then be prescribed those movements that bear distinct biomechanical similarities to their sport situations and enable them to perform better therein. It is highly recommended that all lifters perform the movement with proper form throughout the full range of motion to minimize the risk of injury and ensure even development of musculature. However, it is possible that for those who exclusively specialize in specific tasks, instead of hoping to improve their general fitness and athleticism, even these parameters could be adjusted. For example, if an athlete determined that in their sport they never reached the full depth of the squatting position, instead only having time to half squat during competition, it might be worthwhile to limit the range of motion during training to only what they achieve during competition. This could enable them to save training time, energy, and further develop the attributes of that portion of the muscle, although more research should be conducted into this matter before implementation, as it is currently only conjecture.

When performed properly, squat and deadlift-related injuries are uncommon, which contributes further to the case for utilizing them as major tools for enhancing both exercise and athletic performance. Including these movements in one’s weight training program is not only beneficial because it stresses the muscles and bones, but the connective tissue of various parts of the body as well. This is advantageous because it reduces the risk of injury under loaded conditions due to connective tissue’s ability to adapt over time to resistance training by increasing its integrity (Schellenberg et al., 2013; Swinton et al., 2012).

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