Closing Thoughts
Let's take a step back and examine our risk-to-benefit situation now:
Leg Extension Risks:
1. Increased patellofemoral joint reaction force, knee movement, and joint stress in the most commonly used range of motion.
2. Reduced hamstrings activity.
3. Reduced VMO activity and late onset of firing.
4. Non-existent hip adductor and abductor contribution.
5. Increased rectus femoris firing.
6. Constant ACL tension.
7. Higher patellar ligament, quadriceps tendon, and patellofemoral and tibiofemoral forces with the most commonly utilized loading parameters.
8. Increased lateral patellar deviation.
9. Insufficient involvement of surrounding joints to ensure optimal functioning.
10. Poor training economy (no carryover to closed-chain performance from open-chain exercises).
Leg Extension Benefits:
1. Will give you a good pump, but not even close to the benefits you'll get from squatting and single-leg movements.
2. Uh, wait, there's really only one benefit — and it's pretty weak.
Whether you're a patient or not, the take-home message is the same: if you want more bang for your training buck you should be squatting, not doing leg extensions. Factor in the additional loading that squatting allows, and it should come as no surprise that you'll see better gains in size, strength, and functional capacity.