Leg Extensions Arn’t Worth It
Most gyms have a leg extension machine, and most leg extension machines have their faithful users who come in and risk tearing their knees apart for the sake of working on their quadriceps. The truth about leg/quad extensions is that they are a sub-par exercise which has a high risk of injury. Here’s why you should skip the leg extension machine and what alternative exercises you should be doing to work your quadriceps.
Let’s be honest, having big strong quads is great. These are the most impressive leg muscles and anyone who doesn’t want weird chicken legs should spend the energy to train their quads.
Chicken legs (don’t skip leg day!):
Leg extensions are an isolation exercise which target the quads. That’s the first problem with leg extensions – they are an isolation exercise. Isolation exercises target a specific muscle. This is in contrast to compound exercises which may target a single area of the body, but actually use a lot of different muscles in the body. An example of a compound exercise is the squat. The squat works most of your leg muscles, your butt muscles, your back muscles, your core, etc.
Compared to compound movements, an isolation movement is an inefficient use of your time at the gym. Instead of doing an exercise which works one or two muscles, focus on doing exercises which target a bunch of your muscles. An isolation exercise should not be your main lift of the day. If it is is leg day, leg extensions are the wrong exercise to focus on.
However, isolation exercises are good if you want to focus on a single muscle group. They are often added at the end of a workout routine to give a specific muscle group a bit of extra work. Though isolation exercises should not be your main exercise of the day, there is a place for isolation exercises in most workout routines. But leg extensions should probably not be the accessory exercise you choose.
Injury From Leg Extensions
Leg extensions have one of the highest rates of injury. The reason is that they put a large amount of stress on your knee joints. Anyone who has dealt with sports injuries knows that joints are among the most common places that injuries occur. Leg extensions are dangerous. The injury risks are just too high to justify for a simple isolation exercise.
Leg extensions put a large amount of shear force on the knee. Shear force means that a part of the body is experiencing force in a single direction. In this case all the pressure is coming from the quads, while most leg movements have force from both the quads and the hamstrings. When you perform seated leg extensions your hamstrings are not taut and do not help stabilize your knee caps.
Because the force is from single direction, it is not balanced and causes an unusually high amount of stress on the knee. The leg extension mechanism also moves the tibia bone forward. This is especially dangerous for the anterior cruciate ligament (ACL). Compared to most other leg exercises, such as the squat, leg extensions place an unusually large amount of pressure on the ACL.
Leg extensions also pose a risk of Chondromalacia or “runners knee”. This is a degradation of the cartilage under your knee. The cause of runners knee is the knee cap rubbing again the leg bones. The increase in risk comes from the way leg extensions move your bones. Leg extensions move the knee in such a way that the weakest portion of cartilage is under the most pressure. This is opposite of squats where the pressure is on the thickest portion of the knee cartilage.
Finally, because leg extensions work the quads but not the hamstrings, it is possible to create a muscle imbalance. Most of the human body is made up of opposing muscles which work to move the body back and forth and keep it stable. This is true of our legs – the quads move the legs in one direction, the hamstrings in the other. If one of these muscles is much stronger than the other, then over time, the knee will see a larger amount of pressure from one side than the other. This imbalance can lead to injury.
Avoiding Leg Extension Injury
There certainly are people who do leg extensions on a regular basis and do not suffer any noticeable negative effects. If you have healthy knees, it is possible to use leg extensions as a part of your workout routine without an injury. If you do want to include seated leg extensions in your routine, here’s a few things you can do to lower your risk of injury.
Leg extensions should be done at low weights and high reps. Using too high of a weight is going to be the number one reason for an injury.
Warm up. This is true of just about any exercise. Do not jump straight into your working weight. Warm up your legs by walking or jogging on the treadmill or elliptical machine before you do your leg extensions.
Do not bend the legs past 90 degrees. The more you bend your legs the higher the stress on the knee.
Do not lock out your legs. You can come close to straighting the leg, but do not lock out your knees.
Leg extensions are not functional. The human body never lifts anything using the same mechanics that leg extensions have. When was the last time you sat on a chair and lifted something with your feet by straighting your legs? It doesn’t happen.
The first place to look for a good quadriceps workout is a functional exercise. The obvious answer is the squat. The front squat specifically focuses on the quads more than the back squat. Other forms of squat include the single leg squat and the split squat. Lunges and leg presses are other alternatives that work the quads.
A leg hold using a leg press machine is another good way to strengthen the tendons of the knee by doing a static (isometric) hold. The lack of movement prevents some of the risk of injury described above. Leg holds are sometimes used to rehabilitate injured knees.
There’s a lot of quadriceps exercises which pose less risk than leg extensions and you should consider the alternatives. They usually pose less risk of injury.