We have all been there when our knees are sore, the back is tight, and just don’t want to do squats; even if it could save a life. Yet, even though the lift is the hardest to perform and many skip it altogether, doing squats correctly is very beneficial. If you have done a back squat, there is a good chance that you have at least done one set of front squats in your life. However, do you know what the difference is between the front and back squat; besides just where the bar lays? Let’s dig a little deeper than most bros squats and comparison the biomechanics of front to back squat.
The main difference between a front and a back squat is the bar position. The front squat has the bar placed over the collar bone and anterior deltoids. Back squat has the barbell over the upper trapezius muscles and posterior deltoids. While the bar is only moved a few inches from either position, it dramatically changes where the center of gravity on the body. A quick reminder, the major muscles involved in squat moments are the quadriceps (Rectus femoris, Vastus lateral, Vastus medial, & Vastus intermedium), hamstrings (biceps femoris, semitendinosus, & semimembranosus), gastrocnemius, and the gluteus maximus. The squat is also a full-body lift; relying on muscle activity from the hips and ankle joints as well as the abdominals and spinal erectors. Saying that it is time to get to the goods.
While both the front squat and back squat work the lower back, hips, and legs, because of the bar placement, the technique and maximum amount of weight that someone can lift differ (normally an individual will be able to back squat more). The similarities between the front and back squat have been recognized by professionals, however, there is a common belief that variations can be used to protect and isolate different muscle groups. Front squats are known to hit the quadriceps more and also have greater recruitment for the distal quadriceps (the part by the knee), but do keep in mind there has yet to be a study that truly proves this. We, however, are going to look at the knee join it kinetics while performing the front and back squat.
The Study we are looking at used nine men and six women (22.1 +/- 3.6 years of age) for the process of comparing the two ways to squat. By comparing the net compressive and shear forces applied to the tibiofemoral joint during both lifts, they were also able to look at lower-extremity muscle activity (what muscles were firing). The information was collected by measuring electromyographic (EMG) activity of selected muscles and also six pairs of Ag/AgCl surface EMG electrodes were attached to the right side of the body overlying the muscles of interest. Three genlocked video cameras collecting at 60 Hz and a Bertec force collecting at 900 Hz were used to collect data. The video cameras and force plates were time-synchronized using a Peak Motus video analysis system. With this, they would be able to analyze the squat in 3D (X, Y, & Z). For the tests, each person squatted a load of 70% of their 1RM (rep max). Each trial had three repetitions each was performed for each squat variation.
From the results, the back squat higher maximum compressive force on the knee (11.0 +/- 2.3 N kg 21) than the front squat (9.3 +/- 1.5 N kg 21). Shear forces (slide) at the knee did not vary between the back and front squat. The muscle activity was relatively low during the descent phase compared to when it reached the maximal levels during the up phase. The %MVIC (Maximal voluntary isometric contraction) of the descent and upward phase were significantly different. The semitendinosus had an MVIC of around 100% during the descent and then while the upward phase climbed to 180%. While that is the most significant difference in a muscle, they all were notably different. However, unlike what most of us probably believe, the bar position did not influence muscle activity. There were a few slight differences, the back squat did activate the lower body (legs) a little more; while the front squat, activated the erector spine a few %MVIC more.
At this time, I would like to remind you that the study was having the people do a normal squat, meaning up and down quickly. This was not looking at eccentric work, although, it would seem that to get the most muscle development the concentric phase of the squat is more important; no matter if you are performing front or back squats. When it came to which squat is better for muscle recruitment; the front squat was shown to be just as effective as the back squat in terms of overall muscle recruitment, with significantly less compressive forces on the knee.
For the force on the knee for back and front squat, from the study; “The primary objectives of this investigation were to quantify and compare net compressive and shear forces of the tibiofemoral joint and extensor moments as well as muscle activation while executing front and back squats. However, the limitations of our kinetic analyzes should be stated before discussing the results. The results of any project using inverse dynamics should be interpreted with caution because the resultant forces calculated to represent the net effect of muscle, passive tissue, and joint contact forces. It is impossible to discern the exact contribution that each individual structure contributes to the net force. Future studies could predict forces in individual joint structures using musculoskeletal modeling and optimization techniques.” It seems that this study was not able to show a difference. It is important to note that the back squat had more compression on the knees, but as the study stated, that could be because the back squat has more weight on the barbell.
Gullett, Jonathan C., Mark D. Tillman, Gregory M. Gutierrez, and John W. Chow. “A Biomechanical Comparison of Back and Front Squats in Healthy Trained Individuals.” Journal of Strength and Conditioning Research 23.1 (2009): 284-92. Nyu.edu. Web. 5 Nov. 2015. <https://steinhardt.nyu.edu/scmsAdmin/uploads/006/008/Gullet%20et%20al%202009%20-%20J%20Strength%20%26%20Conditioning%20Research.pdf>.