As the name suggests, isolation exercises work one muscle group hard, whereas compound exercises (like a squat) target multiple muscles and joints together. In the single vs multi-joint resistance exercises (opens in new tab) debate, any strength and conditioning program worth it’s salt will adopt progressive overload techniques using a mix of both, focusing on the compound and adding isolation exercises as accessory moves to the big lifts.
But before we go any further, performing an isolation exercise every day isn’t the best way to build strength and muscle across your body. Over time, exercising this way could put excess strain on the muscle and associated joints. You should always factor in at least 24 hours of recovery between leg day workouts to allow muscles to repair. But for this challenge, I wanted to test higher reps for one week only.
Grab a set of the best adjustable dumbbells to keep on standby for a variation on the leg extension exercise, and read on to see how my legs fared.
Like hamstring curls, leg extensions are typically done on a machine in the gym, but that makes the exercise less accessible for people with limited equipment. The dumbbell leg extension could build size and definition in your quads and can be done anywhere using one dumbbell. Using free weights also helps out-train muscle imbalances and improve cross-body coordination, and research (opens in new tab) suggests resistance band training could offer similar benefits.
This method is accessible for beginners and teaches you the correct way to move with more support for your back. However, your stronger side (we all have one) has the potential to take the brunt, which could create imbalances.
Leg extensions using a dumbbell require more balance, core activation, and better posture. Either method could be added to the end of a strength training program when the muscles are already tired from squats, deadlifts, and other compound exercises. You could adopt drop sets (dropping the weight or reps for extra rounds) or aim for max reps to reach burnout.
Sit upright with your core engaged and grip the sides of your bench
Place a dumbbell between your feet, keeping your legs at 90 degrees
Stay tall as you lift your legs and extend your knees
Pause and squeeze your quads and avoid arching your back or hunching
Never swing your legs or throw the weight. Always move with control. If you can’t extend your knees, decrease the weight to achieve a fuller range of motion.
Leg extensions strengthen the quadricep muscles and attachments at the knee joint. The move allows you to focus on one muscle group while working your knee through full flexion and extension to build strength and muscle.
I used dumbbells for this fitness challenge, tackling six sets of 10 reps — this is more than I would program for clients, but it isn’t outrageous either, as I didn’t want to risk injury. I focused on squeezing my quads hard at the top with a brief pause, then slowly lowered the weight. Fair to say, I had to squeeze every last drop out of the last few reps of each set, and my quads were on fire for days. Reminder — isolation exercises are full-on.
If you have a knee injury, suffer from joint soreness, or have limited mobility, always check with a medical professional before undertaking leg extensions and stop if you experience pain.
Leg extensions catch a bad rep for harming the knees, but there are two ways to look at it. For many people, it’s a great exercise for strengthening the muscles surrounding the knee joint and could protect you from injury. The strength exercise could also help develop muscles required for sports like football (think of how you kick a ball) and sprinting.
Knee pain is mostly a result of loading at the ankles, which puts strain on the knee. Overloading your muscles and tendons could be another cause and can sometimes be rectified by lifting lighter weights. The high reps and daily repetition were certainly too much for me, so I dropped the weight to a lighter load than I’d typically use. It helped me to focus on my full range of motion without overexerting my knees, and this felt far more comfortable while still working my quads hard.
These are the best knee strengthening exercises and yoga for knee pain workout to try.
Machine leg extensions allow you to rest your back which can help improve posture, but performing dumbbell leg extensions just using a flat bench requires more work from your core muscles to sit upright. I found myself excessively leaning forwards, so I spent the remaining days in front of the mirror to keep an eye on my form.
Initially, I felt pressure sent to my lower back and noticed I had curled my pelvis towards my spine. After a quick adjustment and regular check-ins, my core felt switched on and surprisingly achy. And although progressive overload (gradually adapting reps, weights, or other variables over time) doesn’t happen after one week, I began to feel more comfortable as the week went on.
Hardly a shock, but my quads felt considerably weaker during CrossFit workouts throughout the week, and my legs felt overworked. The Journal of Physiology (opens in new tab) explains that micro-tears of the muscle during exercise are a major cause of muscle soreness, known as DOMS (delayed-onset muscle soreness).
I can’t stress enough how important rest and recovery are for helping your muscles repair, recover, and grow. Always allow at least 24 hours after a lower or upper body strength training program, targeting alternate muscle groups throughout the week to avoid over-training.
