reckonerLeg extension
Sit down, straighten your knees against a pad. It is the only movement in the library that trains the quads and nothing else, which is exactly what makes it worth having: there is one part of the quadriceps that squatting has repeatedly failed to grow.
Control the lowering, don't kick.
- Pattern
- Knee isolation
- Trains
- Quads
- Kit
- Machine leg extension
- Loading
- A weight you choose
- Reckoner prescribes
- 3 sets of 10 to 15 reps at RPE 8
- Progression step
- 5 kg once the top of the range is clean
- Skill
- Simple to learn
- Recovery cost
- Low
- Not prescribed if you have declared
- Knee
Muscles worked
How to do it
Set the back pad so your knee lines up with the pivot
Sit fully back and adjust the seat until the axis of the machine is level with the side of your knee. If it is not, the machine is bending you around a joint you do not have.
Set the ankle pad low on the shin
Just above the top of your foot, not halfway up your calf. Too high and the lever is short and the load lands close to the knee.
Straighten the legs and hold for a beat
Push out until the knees are straight and pause. That top position is where the muscle is shortest and it is the part of the range this machine exists to reach.
Control the lowering, do not kick
That is the cue on your wrist. Come back down slowly to a full bend. Swinging out and dropping back is how a stack gets moved without a muscle doing much.
What goes wrong
Throwing the weight out and letting it fall back
The whole return is free training and dropping it gives that away, then hands your knee a load arriving at speed at the bottom. If you cannot lower it under control, lower the stack.
Skipping it because squats cover the quads
Mostly they do, and there is a consistent exception. In a ten week comparison of full and half squats, knee extensor volume rose in both groups while the rectus femoris did not change in either one1. That is the quad head that crosses the hip, and this machine is a direct way to load it.
Loading it like a compound lift
It is a single joint movement on one muscle group, and the stack that lets you do it well is much lighter than your pride expects. Reckoner steps it on the machine stack ladder, which moves in the increments a pin actually offers.
How Reckoner progresses this lift
Six weeks of this lift, from 35 kg, run through the real engine. Nothing below was typed in: the prescription, the decision and the sentence beside it all come from the same code that writes your week.
| Week | Prescribed | What it did |
|---|---|---|
| 1 | 3 x 10 at 35 kg | More reps 10 → 11 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 2 | 3 x 11 at 35 kg | More reps 11 → 12 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 3 | 3 x 12 at 35 kg | More reps 12 → 13 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 4 | 3 x 13 at 35 kg | More reps 13 → 14 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 5 | 3 x 14 at 35 kg | Deload 40% of sets offFive weeks of building, then one week lighter. About 40% of the sets come off. The load holds and your reps stay where you earned them, so you keep the strength and lose the fatigue. |
| 6 | 2 x 14 at 35 kg | More reps 14 → 15 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. The lighter week is over, so this is back to three sets. |
Real engine output, not an illustration. Every row was produced by running the engine itself when this page was generated.
The full rule, and why the reps move before the load does, is in how Reckoner decides to add weight.
Questions people ask
Are leg extensions bad for your knees?
For a healthy knee, done under control at a sensible load, there is no good reason to avoid them. Compressive force through the knee rises as the joint bends and peaks near full flexion2, so the position people worry about is not the one this machine spends time in. If you have a diagnosed knee problem, that is a conversation for whoever is treating it, and the library records a knee restriction against this movement so Reckoner will take it out of your plan if you declare one.
Do I need leg extensions if I squat?
Not necessarily, and they add something squatting has not been shown to. The rectus femoris was unchanged by ten weeks of squatting at either depth1, and it is the one head of the quadriceps this machine can load directly.
Will Reckoner give me this with a knee restriction?
No. Knee is the only restriction the library records against it, and declaring one in setup takes it out of your plan.
Similar movements
Reckoner has no other movement in this swap group.
Sources
- Kubo and colleagues, European Journal of Applied Physiology, 2019. Effects of squat training with different depths on lower limb muscle volumes seventeen men training full or half squats twice a week for ten weeks, knee extensor volume rising 4.9 per cent against 4.6 per cent with no difference between depths, while the adductors and gluteus maximus grew significantly more in the full squat group at 6.2 against 2.7 per cent and 6.7 against 2.2 per cent, and the rectus femoris did not change in either group
- Escamilla, Medicine and Science in Sports and Exercise, 2001. Knee biomechanics of the dynamic squat exercise a review reporting that compressive force at the knee rises as the knee bends and peaks near full flexion, and that the parallel squat is not injurious to a healthy knee. Twenty-five years old, and its advice to prefer parallel over deep is superseded on that point by the 2013 review cited beside it