Isolating your quadriceps with leg extensions could align with your training goals but you still need to do them at the right frequency.
Most people should do leg extensions around 0 (other quadricep exercises) and 2 times a week. With a good workout program, this is often enough to see nice amounts of muscle growth and strength progress.
That being said, bodybuilders who really want to focus on their quads and athletes who want to improve performance in certain leg extension movements can consider doing leg extensions more often.
More specifically, hypertrophy (muscle growth) leg extension workouts can be done up to 3 times a week and potentially more if you don’t push to failure, implement medium to low rep ranges, and take care of your body.
Leg extension strength workouts with lower rep ranges and staying further away from muscle failure can often be done more than 3 times a week without issues.
That being said, there are not many situations where someone would consider doing leg extensions more often than 2 times a week.
How many times a week should you do leg extensions?
Leg extensions can make your thighs bigger but you still have to approach your resistance training sessions the right way.
Even if you do the right amounts of leg extension reps and sets in your workouts, there are other factors like rest (and nutrition) that influence whether and to what extent you will see results.
During resistance training exercises like leg extensions, you damage your quadricep muscles. This is not as bad as it sounds since this starts internal processes that can make the muscles bigger and stronger.
That being said, your body still needs time to repair, grow, and strengthen the muscles. If you do leg extensions again too soon, you will interrupt the processes and reduce your gains.
You should generally only do leg extensions up to 3 times a week maximum. However, for most people and training goals, 0 (other quad exercises) to 2 times a week will offer the desired results too.
Additionally, the 3 times a week guideline is mostly for muscle growth workouts where you implement higher rep ranges and come close to failure.
If you are doing leg extensions to build strength, which means lower rep ranges and further away from failure, you can likely do them more often than 3 times a week in theory.
Doing leg extensions 3 or more times a week is more reserved for bodybuilders who really want to focus on their quads or athletes who want to improve performance in specific movements.
How long should you rest in between leg extensions?
As mentioned above, most people will want to implement at least an extra rest day (48 hours) in between leg extension hypertrophy workouts.
With the right nutrition and sleep habits, 24 hours in between quadricep strength workouts could be enough. Even though there are not many situations where you would want to do leg extensions this often.
Another way to look at this question is how long you need to rest in between leg extension sets. It is generally recommended to rest for 2 to 4 minutes in between resistance training sets.
Lastly, you can also focus on how long you should stay in position after each repetition, especially when your legs are folded.
For this, you simply want to wait around a second to avoid using the bounce of your tendons to move the weight and avoid injuring yourself by doing leg extensions too far and fast.
When should you do leg extensions?
Next, you may wonder when leg extensions should be done in a single workout. More specifically, whether you should start with compound movements like squats or isolation exercises like the leg extension.
It is generally recommended to start with your compound lifts and do isolation exercises at the end of your workout.
For example, you would typically do a few sets of squats before using your leg extension weight bench or machine.
The main reasons for this are that you want enough energy and muscle power to do your compound lifts with good technique and enough strength to push yourself enough to get results.
That being said, there are also some people that do hypertrophy (muscle growth) workouts where they start with something like leg extensions and then do squats after.
You can also start with very light leg extensions to improve mind-muscle connection before your squat sets. This could offer more quad growth and strength progress.