How deep should I squat? A simple question with a slightly more complex answer. Some believe that performing full squats increases the risk of injury, others that they hold almost magical benefits. So, let’s work out which side is closer to truth. The first part of this article will look at some the studies which have examined the effect of squatting with different ranges of motion (ROMs) on muscle activation.
How deep is your squat?
Outlining what we mean when we talk depth would be a good place to start. General consensus gives us these three depths:
Parallel squat – where the top of the thigh is parallel to the floor
Full squat – anything below parallel (also known as ‘deep’ or ‘ass to grass’)
Some call a parallel squat a deep squat. Some call a squat to 90o a parallel squat (even though nothing is actually parallel!). I don’t care what you call them so long as you know the difference.
Breaking it down
Let’s examine some of the parameters which may explain why, or why not, full squats may be superior. We’ll take each one in turn and examine the case FOR and AGAINST full squats being superior in regards to the specific proposition.
- Quad activation
Signorile et al  examined the effect of knee angle (5o, 30o and 90o degrees of knee flexion) on activation of the vastus medialis, vastus lateralis and rectus femoris during isometric contraction. The authors demonstrated greater activation at 90o vs 5o of flexion – the implication that deeper squatting should therefore be beneficial – although this is still very much in the partial squat range.
Ninos et al  recorded EMG for the vastus medialis and lateralis for squats performed between 0-60o of knee flexion (very much a partial squat depth); they reported increased activation of the vastii as depth increased.
Wilk et al  evaluated joint forces and EMG during squatting and leg pressing to depths of approximately 100o of knee flexion. Maximal EMG activity of the quadriceps was reported at the very bottom of the squat (between 88-102° of knee flexion) and start of the concentric phase, activity then decreased in a linear fashion as the knee was extended.
Bryanton et al  measured joint moments and relative muscular efforts (RMEs; expressed as percentages of maximal isometric contraction) of the hip, knee and ankle across a range of squat depths (from 30-120o of knee flexion) and loadings (50-90% full squat 1RM). The authors found that squat depth had a pronounced impact on RME of the knee extensors whereas barbell loading did not – RME was approximately 25% greater in the deepest versus the shallowest ROMs. However, these increases were not linear – RME was greatest between 105-120o of knee flexion, lowest between 30-45o and fairly consistent throughout the mid-range – this suggests that it’s the very bottom portion of the lift that’s most important for the quads. In fact, RME in this bottom ROM with just 50% 1RM was greater than for a 90% load between 90-105o.
Gorsuch et al  compared muscle activation of the rectus femoris during partial (45o knee flexion) and parallel (90o knee flexion – again, I wouldn’t call this ‘parallel’!) squats; squats were performed with a 10RM load which had been determined for each variation. The authors found that rectus femoris activity was approximately 25% higher in the parallel vs partial condition in spite of the lower absolute loading.
Caterisano et al  compared partial (45o knee flexion), parallel (90o knee flexion – erm… parallel?!) and full (135o knee flexion) squats using loads of between 1-1.25x bodyweight and found no effect of depth on the relative contribution (in relation to the glutes and hamstrings) of the vastii. Indeed, the relative contribution of the vastus medialis was actually highest in the partial squat and approached statistical significance (p = 0.07). However, the study didn’t normalise EMG data in relation to maximal contraction and assessed the relative contribution of each muscle to the total amount of EMG activity instead.
Peak RMEs for the knee extensors observed by both Wilk et al  and Bryanton et al  were typically only in the region of 60%. If maximal recruitment of the quadriceps is desired then other exercises are likely to prove more effective choices.
Full range squats provide a greater stimulus to the quadriceps than parallel or partial squats and require less absolute and relative intensities to achieve this.
- Glute activation
Bryanton et al  demonstrated fairly linear increases in hip extensor RME with increasing depth for loadings between 50-80%.
Caterisano et al  observed increases in the relative contribution of the gluteus maximus in their 90o (by 28%) and 135o (by 35%) squats in comparison to those performed to 45o. However, there’s of course the issue that this study didn’t normalise EMG to MVC.
Whilst Bryanton et al  demonstrated linear relationships for 50-80% loadings, for the 90% loading there was no additional increase beyond 75o knee flexion. Bare in mind that loadings were all based on full squat 1RM, partial squats would typically be performed with heaver loadings and may further reduce the impact of depth on glute activity.
Deeper squats appear elicit great gluteal activation on the whole. However, this relationship may not hold true for heavier loads (≥90% full squat 1RM).
- Hamstring activation
Wilk et al  also examined hamstring activation during the squat in their study. The authors reported peak EMG activity between at just 60-74° of knee flexion during the concentric squat and reported maximal values in the region of just 40% MVC.
Gorsuch et al  saw no differences in biceps femoris activation between 45o and 90o squats.
Caterisano et al  demonstrated that depth had no impact on activity of the biceps femoris, accounting for less than 15% of EMG activity in the concentric phase and 10% in the eccentric phase.
Jensen and Ebben  recorded hamstring activation during squats performed to 90o knee flexion. Whilst they observed that hamstring activity initially increased from 30o to 60o of knee flexion during the eccentric phase but there were no differences either beyond this range or at all during the concentric phase.
Squat depth does not appear to influence hamstring activation, however, the role of the hamstrings in establishing effective co-contraction strategies should not be overlooked and warrants more detailed investigation in relation to depth, particularly in the deeper ranges of knee flexion.
- Calf activation
RME of the plantar flexors in the Bryanton study  wasn’t affected by squat depth, only by barbell load. The 90% load typically achieved an RME of about 70%.
Gorsuch et al  echoed the above findings; calf activity was not different between depths of 45o and 90o knee flexion.
Calf activity is does not appear to be impacted by squatting depth.
Despite methodological concerns and inconsistencies, there appears a general consensus that increasing ROM during the squat leads to greater muscle activation of the quads and glutes, but not the hamstrings and calves. Some of the reductions in activation associated with partial squatting may be partially – or entirely in some instances – offset by increases in absolute loading
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2. Ninos JC, Irrgang JJ, Burdett R, et al. Electromyographic analysis of the squat performed in self-selected lower extremity neutral rotation and 30 degrees of lower extremity turn-out from the self-selected neutral position. J Orthop Sports Phys Ther 25: 307-15, 1997.
3. Wilk KE, Escamilla RF, Fleisig GS, et al. A comparison of tibiofemoral joint forces and electromyographic activity during open and closed kinetic chain exercises. Am J Sports Med 24: 518-527, 1996.
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5. Gorsuch,J, Long J, Miller K, et al. The effect of squat depth on multiarticular muscle activation in collegiate cross-country runners. J Strength Cond Res 27: 2619-2625, 2013.
6. Caterisano A, Moss RF, Pellinger TK, et al. The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. J Strength Cond Res 16: 428-432, 2002.
7. Jensen RL and Ebben WP. Hamstring electromyographic response of the back squat at different knee angles during concentric and eccentric phases. In: Proceedings of the XVIII International Symposium of the Society of Biomechanics in Sports, Hong Kong. 1:158-161, 2000.