Leg Extensions vs Sissy Squats

Leg Extensions vs Sissy Squats


Execution Cues:

Leg Extensions:
- Set-up the appropriate machine by adjusting the back and ankle pads if applicable. The back pad should be forward enough to keep your hips at 90º flexion with your knee joints in line with the machine's axis of rotation. The ankle pad should be on the distal part of your shins but not impeding your natural ankle dorsiflexion. Note that a poor set-up can significantly alter the mechanics of the exercise.
- Step into the machine and get seated with your ankles and low back in contact with the pads. Use your hands to grip the handles (if applicable) and pull your hips down into the seat. Your abs should be slightly contracted to eliminate "loose" shoulders. 
- Start the concentric by extending your knees into the ankle pad. Ankles can be dorsiflexed or plantarflexed depending on the goal of the exercise. 
- Continue the knee extension until full lockout. At this point, there should have been near-zero extraneous movement other than at the knee joint. When you reach this terminal end of the ROM, pause briefly in contraction. 
- From here, shift into the eccentric by reversing the motion. Control the velocity of knee flexion by resisting the load all the way down until returning to the start.

Sissy Squats:
- These can be set-up in a few different ways depending on how active the upper body will be in stabilizing. I recommend setting up a barbell in a rack to about belly button height but any stable object will do as long as there is room to perform the movement and the source of stability doesn't pull you out of position. 
- Assuming this object is in place and solidified, stand tall next to it with your feet 4-6 inches apart. Externally rotate your feet to your degree of comfort and according to your anatomy (this will typically be 10 and 2 o'clock). Place your hands on your chosen object of stability. Fully extend your hips, contract your glutes and shift your pelvis into a neutral position.
- Begin the eccentric by shifting your weight into the balls of your feet and allowing your heels to come off the ground. Push your knees forward over your toes while maintaining the positioning from the knees up. Hips should remain extended. 
- Continue to allow this controlled knee flexion as your knees translate further forward. Depending on your initial setup, the eccentric will either see your torso coming OR shins coming closer to parallel with the floor. If it is the former, there will be more stretch/lenthening at the proximal to the hips. If it is the latter, the tension will be closer to the knees and distal to the hips. This can be adjusted depending on goals though this is outside of our scope here. 
- The terminal end of the ROM should be marked by an inability to get any more knee flexion OR maintain trunk/hip positioning. Once this point it reached, carefully transition into the concentric by extending the knees all the way until you're standing upright once again with feet flat on the floor. 
- Note that the upper body should be used for balance and stability rather than to pull yourself up. Assistance should be used as needed but be aware of this differentiation.

Key Similarities: 
- Single joint quad movement that maximizes torque around the knee⁣
- 10-20 rep range is generally most optimal 
- Both find the most benefit with deliberate extensions of tempo (mainly slow eccentrics)
- Though each of these movements have a poor reputation when it comes to knee health, they can actually strengthen the knees and improve joint integrity when done properly (and with a well-designed machine).
- Non axial loading which allows for a bit more creativity within programming
- Well-suited for supersets and circuits
- Can be used to achieve additional quad volume through increased frequency within a microcycle

Key Differences: 
- Leg Extensions bias the shortened fiber length while Sissy Squats aim to lengthen the quad fibers.
- A machine is needed to get the most out of this Leg Extensions, and replicating it with DBs, cables, bands, etc will significantly reduce its efficacy. Conversely, no machine is needed for Sissy Squats which increases the practicality of use especially when training from home⁣.
- Sissy Squats have an ascending strength curve meaning that the tension being applied is increased through the eccentric and decreases through the concentric (i.e. it’s hard at the bottom and easy at the top)⁣. But Leg Extensions' strength curve is flat (for most machines) meaning that the tension being applied is consistent at all joint angles⁣.
- Leg Extensions are an open-chain movement with increased stability meaning higher potential to fully exhaust all muscle fibers without external failure points⁣. Sissy Squats are a closed-chain movement with stability decrements leading to potential failure points external to the quads, though holding onto something to stabilize with the upper body can alleviate some of these issues. ⁣
- Sissy Squats have a much stronger mobility component due to the stretch being applied on the quads and hip flexors as well as the demands at the feet and ankles. 
- Sissy Squats can withstand lower rep ranges a bit better (i.e. <8) while Leg Extensions can be more easily work in high rep ranges (i.e. 20+)
- Sissy Squats will cause more muscle damage due to lengthening fibers whereas Leg Extensions can create more metabolic stress. 
- The resistance of Leg Extensions can be easily manipulated. Sissy Squats are relatively bound to working with bodyweight outside of creative solutions (especially when trying to add more load). 
- Leg Extensions have a very low skill prerequisite whereas Sissy Squats actually have a decently high barrier here. This means that beginners or trainees with poor proprioception and coordination may be better suited to start with Leg Extensions as they become more proficient. 
- Leg Extensions cater well for intensity techniques while Sissy Squats do not.

Primary Use Case for Leg Extensions:
- Hypertrophy of the Quads

Primary Use Case for Sissy Squats:
- Hypertrophy of the Quads

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