Is It True That Leg Extensions Bad for Your Knees?

If you are wondering if leg extensions are bad for your knees, then you’ve come to the right place.  This is one of the most popular exercises in every gym across the nation.  It’s usually the most loved exercise as well because it’s simply an isometric movement.  Isometric exercises are usually a bit easier than compound movements such as the squat.  Let’s get into the issues of some leg exercises and your knees to better understand all the confusion.

What Exactly is Weight Training?

Weight training is a form of strength training that uses weights for resistance.  By creating a stress to the muscles executed with weights, it will cause the muscles to be activated and become larger and stronger.  Weight training can be done using machines and free weights such as barbells and dumbbells.  A beginner can take full range in the gym in regards to exercises, reps, and sets.  This is because resistance training is new to the muscle and results come quickly.

Once the newness wears off and results slow down, then the lifter might look into tweaking his or her exercises, reps and sets.  To move into intermediate and advanced training, it can be broken down into two forms:

• Sub-Maximal Effort Training
• Maximal Effort Training

These training platforms can be used in the same workout.  It’s important to know and understand each so you don’t cause muscle injuries.  Let’s cover each so you get a better understanding.  The more you know, the more you grow.

Sub-Maximal Effort Training

Sub-maximal effort training (sub-maximal training, sub-maximal strength training) is weight training with loads that don’t require maximum effort.  The poundage used is 50-75% of your 1 rep max (1RM), but not exceeding 85% according to American Council on Exercise (ACE).  Sub-maximal training allows you to weight train in a rep range that provides results and still have energy left to complete a few more reps if you wanted to.

Maximal Effort Training

During maximal effort training (maximal training, maximal strength training) the lifter trains using heavy loads.  These loads are in the 90% range of their 1RM.  When you exert maximum effort into a single, heavy rep, you build muscle coordination and strength, as well as neurological development.  Max-effort training is usually 1-5 reps, even up to 8 at times.  With max-training you are taking each set to complete failure where you cannot complete one more rep with good form.

Leg Extensions Bad for Your Knees?  [TRUTH]

So, let’s get to the notation that leg extensions are bad for your knees.  There’s is some truth and even false to this statement.  Let’s look at how most people train with leg extensions.  Most lifters using the leg extension machine heave the weight up to get it going.  In addition, they don’t lock out at the top. Then, the weight free falls and the lifter get a little rebound in the bottom, allowing moment to take over.

The leg extension is an isometric exercise.  “An isometric exercise refers to an exercise that uses a static muscle contraction. This means that the muscle group being worked is under tension and producing a contraction but the muscle doesn’t change length. Therefore, the joints involved do not move,” states Nick Dewey, Physiotherapist at Sport & Spinal Physiotherapy.

Leg extensions are a notable exercise for strengthening the patellar ligament and quadriceps attachment for the knee.  Extensions are also a good finisher exercise after you performed your compound exercises such squats, lunges, and stiff-legged deadlifts.

Leg extensions work wonderfully when sub-maximal training is applied.  This means to use a weight load of 50-75% of your 1RM.  In doing so, you will be able to do 12-15 reps and still have fuel in your tank.  Going heavy on leg extensions in the 6-10 rep range can damage your knee joints over time.  Simply put, maximal-effort leg extensions are useless and even dangerous.  When you do leg extensions, you should do sub-maximal leg extensions to be safe on your knee joints.

Here’s the Right Way to Do Leg Extensions

We will perfect two key points to fully stimulate your quads using the leg extension machine.  Use sub-maximal training by choose a poundage in which you can compete at least 12 reps with, using perfect form.  With every rep, you will want to get a complete lock-out at the contraction point.

Here’s how to do the leg extension properly.  From the starting point with your legs relaxed, bring the weight up and lock out and contract hard at the top, holding it for a full second.  At the contraction point, try and lift your knees and lower quads off the bench.  This will ensure a nice and hard contraction.  Next, in a controlled fashion, lower the weight, feeling the negative as the weight returns to the starting point.  The harder you hit each contraction; the more muscle growth will occur.

Which is Ideal Training, Sub- or Max-Effort Training?

Both forms of training, sub- and max-training have their place in a muscle-building program.  The trick is to know when to use each.  For best results, start your training with a compound exercise such as squats or leg press.  With compound movements you can train using maximal-effort training, utilizing loads 75-90% of your 1RM.  This is ideal for adding mass.

Once your compound exercises are out of the way, start with your isolation exercises such as leg extensions and leg curls.  These are the exercises that you should utilize sub-maximal effort training. using loads 50-75% of your 1RM.

Final Thoughts on Leg Extensions…

So, the idea that leg extensions are bad for your knees really depends on your training. The leg extension is a good exercise when it’s performed using lighter poundage in the 12-15 rep range, as you would do with sub-max training.  There is no need in going heavy using low reps with the leg extension.  Doing so will damage your knees over time.  Use lighter weight and focus on the contraction.  Get more leg training hacks.  See below…