Activating the quadriceps clearly depends on the goal in mind. In this case, we are emphasizing strength development over everything. This blog is based on the most effective, evidence-based ways to efficently develop strength in the quadriceps
One of the number one scientifically proven ways to recruit more motor units in the quads is by simply performing “Closed Kinetic Chain Movements”. One of the most notorious CKCMs is the squat, which has been known to be highly efficient for developing the quads… Whether that is strength, hypertrophy, rehabilitation, corrective, etc. they are a staple functional activity.
Studies show higher EMG (electromyography) activity in the quadriceps during CKC compared to open chain in many contexts (Escamilla et al., 1998; Boren et al., 2011).
https://pubmed.ncbi.nlm.nih.gov/23316425/
Now, let’s dive into why both back squats and front squats are so effective for quadriceps strength development, backed by biomechanics and science:
High mechanical load. High motor unit recruitment!
- Complex, compound, multi joint movements that place large loads/stress on the body.
- In order to move these heavy loads, the body needs to be able to recruit high levels/amounts of motor units.
- This includes all 4 of the quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius).
Joint angle mechanics
- The favoring of quad activation! Both forms of the squat involve knee flexion & extension, which is the primary movement for quad activation (knee dominant musculature).
- The quads are recruited during the eccentric (active knee flexion) to aid in controlling the descent.
- During the concentric or active contraction phase of the quads (driving phase, active knee extension), they are heavily responsible for extending the knee, fighting against natural force (gravity) & the load of the bar.
Front squat quad bias
- Bar loads in the front of the body (anterior chain), allowing for more of an upright kinetic chain posture, shifting the knees forward, & increase the moment arm. This happens by reducing hip flexion & increases knee flexion dominance, allowing for more load to shift onto the quads.
- EMG studies show greater quadriceps activation in front squats vs back squats (Gullett et al., 2009). https://pubmed.ncbi.nlm.nih.gov/19002072/
- In this study, the vastus medialis exhibited greater activation during the front squat compared to the back squat, particularly during the ascending phase. No significant differences were observed in the activation of other muscles. https://pubmed.ncbi.nlm.nih.gov/25630691/
ROM & tension experimentation
- Feel free to utilize deeper ranges of motion, integrate higher amounts of time under tension & stretch tension to best suit your training style/goals/abilities.
- Evidence has shown integrating increased ROM training throughout squat exercises can enhance activation in all quadricep musculature, primarily enhancing fiber activation in the vastus medialis (oblique) VMO.
Progressive overload
- Both versions of these squats can be extremely beneficial for utilizing progressive overload techniques.
- You can load them safely with barbells, use tempo variations, and modify stance to challenge the quads differently.
- I will say that it comes to a point where you can no longer endure the barbell compressive stress due to the stability & strength demands, therefore causing limitations as you start to increase loads. You can add in something like the smith machine if you really need to go heavier. With that being said, loading the BB properly for PO techniques works just fine. No need to ego lift to exponentially develop.
Peer review articles:
https://pmc.ncbi.nlm.nih.gov/articles/PMC5744434/
Resistance Training with Single vs. Multi-joint Exercises at Equal Total Load Volume: Effects on Body Composition, Cardiorespiratory Fitness, and Muscle Strength
https://pubmed.ncbi.nlm.nih.gov/25630691/
Kinematic and EMG activities during front and back squat variations in maximum loads
https://www.researchgate.net/publication/275278734_Quadriceps_effort_during_squat_exercise_depends_on_hip_extensor_muscle_strategy
Quadriceps effort during squat exercise depends on hip extensor muscle strategy
https://journals.lww.com/nsca-jscr/fulltext/2009/01000/A_Biomechanical_Comparison_of_Back_and_Front.41.aspx
Front squat & back squat comparison article
https://www.researchgate.net/publication/377809691_The_effects_of_squat_variations_on_strength_and_quadriceps_hypertrophy_adaptations_in_recreationally_trained_females
The effects of squat variations on strength and quadriceps hypertrophy adaptations in recreationally trained females
https://ijspt.scholasticahq.com/article/94600-a-biomechanical-review-of-the-squat-exercise-implications-for-clinical-practice?utm_source
A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice
https://pubmed.ncbi.nlm.nih.gov/19204567/
Both squat variations resulted in similar quadriceps activation, but front squats led to significantly less compressive forces on the knee, suggesting a safer alternative for individuals with knee issues.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7241635/?utm_source=chatgpt.com
No significant differences in muscle activation were found among the three squat variations, suggesting that front squats are comparable to other squat types in activating the vastus lateralis.
