Leg extensions are often slammed as being “bad for your knees” or “useless for building muscle.”
While they certainly have the potential to be bad for your knees if they’re not done properly, they’re also a very useful way to develop your quads.
While the squat leads to high levels of muscle activation in vastus lateralis and vastus medialis (two of the four muscles that make up your quads), the leg extension has been shown to preferentially recruit rectus femoris, which is the muscle running down the front of your thigh .
In fact, the leg extension, performed three times a week for three months, leads to faster growth in rectus femoris compared to the other three muscles that make up the quads .
Leg extensions have also been shown to reduce knee pain.
In a 2016 study of volleyball and basketball players who’d been suffering from patellar tendinopathy (also known as Jumper’s Knee) for over three years, performing the leg extension three times a week (4 sets of 8 reps, with a 3-second concentric and 4-second eccentric) for a month led to a significant reduction in knee pain and improved function .
Of course, there will be times when the leg extension isn’t appropriate, such as in the early stages of a program designed to rehab an injured ACL, or if it just bothers your knees.
But if you want to build bigger quads, there’s no good reason why the leg extension can’t form of a training program designed to do exactly that.
Christian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former “trainer to the trainers,” he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.