Stop avoiding the leg extension machine if you want bigger, stronger legs. Bonus: It’ll make you better at the big lifts. Here’s why.
The leg extension machine has a bad reputation. It’s known as the machine lifters do when they just want to avoid harder compound lifts. But does that mean it’s useless? Of course not.
Here’s how to get the most out of the leg extension machine and the truth about what it will and won’t do for you.
Leg extensions are a great way to place targeted tension through your quads. You don’t need a study to know it’s working. Exercises like these – that target the shortened range a little more – are notorious for their isolated squeeze and the burn that comes with it.
Some may argue that multi-joint exercises like squats and leg presses are enough to build strong quads. While squats activate three out of the four quadriceps muscles, they’re not as effective at activating the rectus femoris, the quad musculature that runs down the middle of the thigh. Supplementary exercises, like leg extensions, can address this shortcoming.
Leg extensions activate this area greater than squats (1). The timing of activation is also different (2). That makes the leg extension a good side dish to your meat-and-potatoes entree.
Always consider the risk-versus-reward ratio of any exercise. It’s person-specific. Leg extensions have both negative and positive impacts, depending on your circumstance. Numerous studies and real-world results show that leg extensions are beneficial in rehabilitating knee injuries, such as patellar tendinopathy.
Leg extensions provide a controlled environment where the load and range of motion can be carefully manipulated over time. For example, you could only extend your knee from 90 to 45 degrees (where load under the knee cap is lowest), then, as pain-free ranges of motion improve, explore ranges closer to full knee extension. You can also do them for eccentric strengthening protocols, which further benefits tendon health and loading capabilities.
Some argue that leg extensions are bad for the knees, but this isn’t true if you’re doing them correctly with an appropriate weight for your capabilities.
And they’re “bad for the knees” comparable to what? Leg extensions shouldn’t scare you if you’ve spent any time playing a field sport involving change of direction, unpredictability, and human collision. Heck, you’re more likely to injure yourself taking the dog for a walk!
Did you know the ACL can withstand roughly five times the force a leg extension machine can provide with virtually any weight and rep scheme?
The health of the ACL also depends on the strength of your hamstrings. If you’re not giving your hamstrings and glutes enough attention, then an increase in isolated quad strength may increase your risk of ACL injury. So, don’t be weak or have strength imbalances, and you’ll do a lot better than those arguing that leg extensions are bad for your knees.
Consider exercise selection carefully to manage fatigue in your program. Leg extensions produce very little neurological fatigue, making them easier to recover from compared to big lower-body lifts. This is a good reason to sprinkle them in to complement, rather than detract, from your compound lifts.
Leg extensions are a good supplementary exercise for building the quads in those who can perform them pain-free, have good strength symmetry, and devote time to training their hamstrings and glutes as part of a well-balanced training plan.
Be aware. If end-range knee extension causes pain, then avoid that range of motion. On the other hand, you may also change the setup of the leg extension machine and use a foam pad to increase range of motion at the bottom, and benefit from that hypertrophy stimulus.
Overall, exercises and training methods should not be labeled as “good” or “bad.” Context is always key. If you’re concerned with heavy leg extensions, aim for 15-25 reps performed close to failure. For everyone else, sets of 10-15 reps will generally work best.
- Ebben, W., Feldmann, C., Dayne, A., Mitsche, D., Alexander, P., & Knetzger, K. (2009). Muscle activation during lower body resistance training. International Journal of Sports Medicine, 30(1): 1-8.
- Stensdotter A., Hodges P., Mellor R., Sundelin, G., Hager-Ross, C. (2003). Quadriceps activation in closed and in open kinetic chain exercise. Med Sci Sports Exerc, 35(12): 2043-7.