The leg extension is a popular, effective isolation exercise for the quadriceps. For many, it is a finisher after the main leg workout — the squat and/or leg press. Although apparently a simple exercise, a lot can still go wrong with leg extensions.
1. TOO SMALL RANGE OF MOTION
You don’t do leg extensions for your ego, but for your quads. For maximum contraction at the top and stretch at the bottom, set the machine to maximum range of motion (ROM). So go with your legs as deep and as high as you can.
Hold the peak contraction for a second or so, because that will stimulate your quadriceps in a way that squats can’t. Then lower the weight in a controlled manner until you click the weights in the weight drawer — only then the repetition is complete.
Make sure you always use the same ROM and therefore always adjust the device in the same way. Only in this way can you truthfully measure your progress.
2. NOT SITTING PROPERLY IN THE CHAIR
Sit in the chair so that you are comfortable and the end of the seat surface is at the bend of your knee. Your back is then largely against the back surface. If you sink too far forward, it will be at the expense of the ROM.
3. NOT PROPERLY ADJUSTING THE FOOT PAD
For optimal ROM, place the foot pad over the lower part of your leg, where you bend your ankle.
With leg extensions there is no magical width between the legs or position of the feet (pointing in or out); the nuances in quadriceps stimulation are negligible.
4. TOO MUCH BODY ENGLISH
Leg extensions are typically one of those exercises where many try to use as much weight as possible, sometimes the highest weight in the stack. However, do not ask about the performance, because usually all kinds of other muscles suddenly participate in the exercise.
Remember that the leg extension is an isolation exercise for the quadriceps. Your hamstrings, glutes and other muscles should be kept out of the movement.
5. USING TOO MUCH WEIGHT
Precisely because leg extensions are an isolation exercise, you should not use too much weight for safety reasons.
Unlike compound exercises like the squat, your quadriceps are alone. With isolation exercises such as leg extensions and, for example, biceps curls, you train a little more for the pump, so in the range of 10 to 30 repetitions. In addition, you prevent cheating, as discussed in point 4.
Finally, you may benefit from applying different rep ranges, especially as a more experienced strength athlete. Since high repranges in squats killing are, you keep those for the leg extension.