Saturday, February 18, 2017

Barbell Squats - Research Update: Bar Placement, ROM and Muscle Activation | Plus: What's 'Best' for Strength & Size?

Where on your traps you place the bar makes a huge difference in biomechanics.
This is not the first article in which I try to shed the light of science on the effects of full vs. partial squats. The effect of where you place the bar during the barbell back squat, however, hasn't been addressed in detail in previous SuppVersity articles.

In fact, I would guess that the novices among the SuppVersity readers may not even be aware that where you place the bar on your traps may significantly affect your biomechanics and, eventually, your training outcomes.
Learn more about the squat and related exercises at the SuppVersity

Partial Squat = Full Strength

100 Body Weight Squats ➯ Jacked

Discontinue Sets Up Your Gais

Full ROM ➯ Full Gains!

Full-Body vs. Split for Athletes

Squat, Bench, Deadlift for Gainz
As Glassbrook et al. (2017) point out in their latest paper, there are two different variations of the back-squat, differentiated by the placement of the barbell on the trapezius musculature. More specifically, there's
  • the traditional “high-bar” back-squat (HBBS) which is performed with the barbell placed across the top of the trapezius, just below the process of the C7 vertebra, and is commonly used by Olympic weightlifters to simulate the catch position of the Olympic weightlifting competition lifts; the snatch and clean and jerk and, conversely...
  • the “low-bar” back squat (LBBS) where you place the barbell on the lower trapezius, just over the posterior deltoid and along the spine of the scapula, and which is commonly used in competitive powerlifting as it may enable higher loads to be lifted (32).
If you've paid attention in your physics classes at school, you will know that the bar-placement will directly affect your body's center of mass. With the LBBS squat maximizing the posterior displacement of the hips, and increased force through the hip joints in comparison to the knee joints. Details about the potentially far-reaching effects of the modified center of mass are scarce. Glassbrook et al. even go so far to say that "there is no consensus as to the differences between the two back-squat barbell positional variations". Accordingly, the goal of their study was to "compare and contrast the differences in joint angles and Fv of the HBBS and LBBS, up to and including maximal effort, in an effort to create a full profile of the two BBS variations in groups both well versed and newly introduced to these movements" (Glassbrook 2017).

Where you place the bar depends on your sport.

For their study, the scientists from the  Sports Performance Research Institute New Zealand  and the High Performance Sport New Zealand recruited six male powerlifters (height: 179.2 ± 7.8 cm; bodyweight: 87.1 ± 8.0 kg; age: 27.3 ± 4.2 years) of international level, six male Olympic weightlifters (height: 176.7 ± 7.7 cm; bodyweight: 83.1 ± 13 kg; age: 25.3 ± 3.1 years) of national level, and six recreationally trained male athletes (height: 181.9 ± 8.7 cm; bodyweight: 87.9 ± 15.3 kg; age: 27.7 ± 3.8 years). All subjects performed the LBBS, HBBS, and both LBBS and HBBS (respectively) with weight up to and including 100% of their individual 1RM. 
Figure 1: Representation of the order of familiarization and testing dates for the comparison group (Glassbrook 2017).
As the authors point out, only a small to moderate (d = 0.2-0.5) effect size difference was observed between the powerlifters and Olympic weightlifters in joint angles and ground reaction forces (Fv) -with none of them achieving statistical significance. 
Figure 2:  Distance of center of pressure to bar results at 74-100% 1RM; negative numbers indicate a distance behind the center of pressure; the higher this number the greater the involvement of the posterior chain and the lower the contribution of the knee musculature; note: for Gymrats the difference is much smaller than for the extremes, i.e. the Olympic lifters with their high bar and the powerlifters with their low bar placement (Glassbrook 2017).
The latter is in contrast to the significant difference between pros (O-lifters and powerlifters) and recreational athletes where the joint angles and thus the positioning of the bar relative to the center of gravity differed significantly. This observation clearly underlines the effect of resistance training experience and technical proficiency but does not contribute significantly to the scientists' conclusions that ...
Effects of bar placement (originally by Mark Rippetoe).
  • practitioners seeking to place em-phasis on the stronger hip musculature should consider placing the bar in the lower position (LBBS) to increase the distance to the center of mass.
  • practitioners who want to lift the greatest load possible should likewise prefer LBBS 
  • practitioners who train for sports with a more upright torso position (such as the snatch and clean) should rely on the high bar placement and thus a lower distance between bar and the center of mass, which will emphasize the musculature of the knee joint
Similar practically relevant conclusions can also be derived from da Silva's 2017 paper on the muscle activation during the partial and full back squat. As previously pointed out, it is by no means the first investigation into the differential muscle activity of full (or deep) and partial barbell squats, but there's something that makes it particularly interesting.

How deep you should squat depends on your goals.

In contrast to other studies, da Silva, et al. (2017) decided to accommodate for the changes in external load (you can obviously lift much more on the partial squat), which would, in turn, affect and thus mess with the EMG results. In their study, the comparison was, therefore, load-equated and should thus give us an excellent idea of the individual effect of doing full vs. partial squats irrespective of the increased load you can lift if you don't go all the way down.
"Our study utilized a randomized and counterbalanced design with repeated measures to evaluate muscle activation between the partial and full back squat exercise with relative external load equated between conditions. All subjects performed a ten repetition maximum (10RM) test equated for each back squat condition (partial and full back squat). The range of motion was determined by an electrogoniometer on the knee oint, and all subjects performed both conditions in a self-selected cadence. Surface electromyography was measured from the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), erector spinae (ES), soleus (SL), and gluteus maximus (GM). All electromyographic data were defined by the electrogoniometer data, characterizing both the concentric and eccentric phase of each repetition. The rating of perceived exertion (RPE) was evaluated after each back squat condition" (da Silva. 2017)
With 3-7 years of strength training experience, the 15 subjects in da Silva's study were also better trained than the participants in a lot of other studies - a fact of which the previously discussed paper by Glassbrook showed that it can make a significant difference in terms of how the squat is performed and thus how the individual muscle activity is affected on the testing day, when the subjects performed one set of 10RM for each back squat condition:
  • partial back squats with 0-90° knee flexion and 
  • full squats squats with 0-140° knee flexion.
The subjects’ feet were positioned at hip width and vertically aligned with the barbell position. The barbell was positioned on the shoulders (high-bar position) for all subjects and experimental conditions. A rest period of 30-min was provided between conditions.
Figure 3: Mean and standard deviation of RMS EMG in different back squat conditions (partial and full). *Means significantly less between amplitudes, p < 0.05 (da Silva. 2017), vastus lateralis (VL), medialis (VM), rectus femoris (RF), gluteus maximus (GM), biceps femoris (BF), semitendinosus (ST), soleus (SL), erector spinae (ES).
The data-analysis showed similar overall muscle activation patterns of the quadriceps femoris with both versions of the back squat. A significantly higher muscle activation of the gluteus maximus, biceps femoris, and erectors spinae, however, was noted in the partial versus full condition.
Contreras et al. (2016) recently com-pared the muscle activity in partial vs. full back vs. front squats. Going deep on both front and back squats increa-sed the vastus lateralis activity but decreases glute+hamstring activity.
Lower activity, greater gains? No, the results of the study at hand are not unique. Only recently Crontreras et al. saw a similar superior effect of partial squats on the peak and avg. activity of the lower glutes and hamstrings (see figure to the left). But don't worry: As explained below, the fact that the overall increase in leg lean mass tends to be greater in previous studies with the full squat could be due to (a) an increased total workload (measured as weight x distance the weight travels) and (b) training the muscle at long muscle lengths. The latter would be in line with the previously discussed observations from Drinkwater et al. (2016), who observed greater increases in muscle size, but smaller increases in strength (which rely at least partly on optimized muscle activation patterns and may thus be better predicted by EMG measures) in their 2016 study.
This may come as a surprise, as Bloomquist et al. (2013) and McMahon et al. (2014) "have shown superior muscular hypertrophy" (da Silva. 2017) when squatting through the full range of motion. Whether this effect is, in fact, a result of an increased muscle activity or, as da Silva et al. speculate, a simple consequence of an extension of the time under tension remains elusive because there's no muscle activation data available for the Bloomquist study. Accordingly, full squats wouldn't build more muscle because of an increased muscle activity, but despite a lower muscle activity and due to an increased training volume (measured as weight x distance across it was moved).
Figure 4: Total leg lean mass and individual CSA changes in the front and back thigh in the Bloomquist study.
In addition to the volume, the repeatedly observed superior hypertrophic response to full vs. partial squats may, as da Silva et al. likewise point out, as well be "be due to training at long muscle lengths, which has been shown to promote greater increases in cross-sectional area compared to training at shorter muscle lengths" (da Silva 2017; cf. Noorkõiv 2014). The latter may, in fact, have a profound effect on the adaptive response that overrides the already small benefits in muscle activity da Silva et al. observed in the study at hand.
The "optimal" squatting depth (and positioning of the bar) will always depend on your individual biomechanics, your squatting technique and - most importantly - your individual training goals. Drinkwater et al., for example, have shown in their 2016 study that found superior strength increases with partial vs. full squats. Their study should remind you that what's "optimal" will always depend on your individual biomechanics, your squatting technique and - most importantly - your individual training goals.
So what's the verdict, then? Training with a low bar position over the full range of motion will probably yield the greatest gains in total leg mass. That's at least what the individual results of the two studies at hand and the previously discussed evidence of a superior hypertrophy response to squatting over the full range of motion (Bloomquist 2013; McMahon 2014) suggest. With the increased muscle activity during the parietal (90°) squat and the results of the previously discussed study by Drinkwater, et al., however, there's partial squats, especially if they are done with the maximal weight you can lift for a given number of reps, may eventually be the better choice for athletes looking to maximize strength, not size gains.

Eventually, it is important to understand, though, that it would be dumb to assume that there's a 'single best way of squatting' that works for everyone. After all, individual biomechanics, your squatting technique and, most importantly, your training goals and the requirements of your sport will always determine what's "optimal" for you during a specific phase of your training | Comment on Facebook!
References:
  • Bloomquist, K., et al. "Effect of range of motion in heavy load squatting on muscle and tendon adaptations." European journal of applied physiology 113.8 (2013): 2133-2142.
  • Contreras, Bret, et al. "A comparison of gluteus maximus, biceps femoris, and vastus lateralis electromyography amplitude in the parallel, full, and front squat variations in resistance-trained females." Journal of applied biomechanics 32.1 (2016): 16-22.
  • da Silva, Josinaldo Jarbas, et al. "Muscle Activation Differs Between Partial And Full Back Squat Exercise With External Load Equated." The Journal of Strength & Conditioning Research (2017).
  • Glassbrook, Daniel J., et al. "The high-bar and low-bar back-squats: A biomechanical analysis." The Journal of Strength & Conditioning Research (2017).
  • McMahon, Gerard E., et al. "Impact of range of motion during ecologically valid resistance training protocols on muscle size, subcutaneous fat, and strength." The Journal of Strength & Conditioning Research 28.1 (2014): 245-255.
  • Noorkõiv, Marika, Kazunori Nosaka, and Anthony J. Blazevich. "Neuromuscular adaptations associated with knee joint angle-specific force change." Medicine and science in sports and exercise 46.8 (2014): 1525-1537.