Need to isolate your quads? Love hitting them with leg extensions? Great! But you're probably shortchanging yourself on them.
The rectus femoris extends the knee and flexes the hip. So to get a truly full contraction, the hip must also flex instead of staying idle in a traditional leg extension.
To do this, add a hip hinge (bend forward) as you extend the knee. Once the concentric or lifting phase is completed, slowly lean back into the seat as you lower your legs to get back into a stretched position. This subtle change allows you to get more degrees of motion via hip flexion.
Note: I know it looks like I'm rounding my back instead of hip hinging in the video. That's because the tank top I wore was quite long on me. (5'4" problems. Anyone relate?)
Silly or Useful?
Think about it: Lifters often manipulate hamstring exercises by leaning forward on seated leg curls or elevating their toes on RDLs. I know this exercise looks a little weird – maybe really weird – but try it before you knock it.
Once you give it a shot, you'll feel a deeper contraction than you're used to on standard leg extensions. You'll also notice that the added hip hinge forces you to control the movement instead of kicking with momentum.
How to Program It
You could either replace your regular leg extensions with this or do it on a separate day.
My recommendation? Do it with high reps toward the end of a workout. Go to failure or very close. Let me know how flaming hot that burn in your quads gets.