Here's what you need to know...

  1. The leg extension machine stresses out the knees. Use blood flow restriction training to increase its efficacy by creating cumulative stress in the muscle using less weigh.
  2. Standard lunges cause knee pain for many. Either use stationary lunges or reverse lunges to remove stress from the knee and activate the glutes.
  3. Running is hard on the knees. Swap it for incline treadmill walking or add variety using sprints and Fartlek-style running.

If the exercises you love are wrecking your body, swap them out. Or at least be open minded enough to try these modifications. Here are three swaps for the most notorious knee-crushing exercises.

1 – Leg Extensions

The leg extension machine has been demonized in the fitness industry for the last two decades. It's accused of creating chronic knee irritation by creating highly compressive forces at the patella-femoral joint, leading to breakdown of the joint surfaces. It's even called out by coaches, physical therapists, and biomechanists because it's an "open chain" exercise unlike a squat or deadlift.

These are all valid points, but the leg extension is also responsible for helping build some of the most impressive quads in bodybuilding. It continues to be a staple in many programs because it produces results for those wanting muscular hypertrophy. So what's the answer if you want tree trunks for legs AND knee health? Modification. And maybe even replacing it with something to protect the knees for the long haul.

A Better Exercise – Rear Foot Elevated Split Squat

While fatiguing muscular fibers in the quads is guaranteed on the leg extension machine, that same recruitment can be possible through split stance loaded variations such as the lunge or split squat. If you've proved the ability to dominate a static split squat and earned the right to progress, try the rear foot elevated split squat.

This has the ability to create massive amounts of mechanical and metabolic stress in the quadriceps and the posterior chain stabilizers, making it a more highly transferrable exercise without losing any of the quad-targeting the leg extension is known for. If you're searching for a way to elicit as much pain as possible, give this a shot. When your quads lock up after a set you'll have all but forgotten about the leg extension.

How to Keep the Leg Extension, If You Must

You can continue doing leg extensions using blood flow restriction training (BFR). When executed properly, it can lead to an immense amount of muscle growth with a fraction of the external load that's commonly associated with increasing shear and compressional forces at the patella-femoral joint.

Get some elastic straps or wraps, and wrap your thighs as high as you can get them on the hip towards the proximal gluteal fold. Be sure they're at a perceived eight-tenths tightness – pretty damn tight. Once they're on, complete multiple high rep sets, think 15-20 reps, all with 30-40% of your 1RM. Maintain constant tension and flex each rep to drive more and more blood into the quads. Keep rest periods short. Anywhere from 20-40 seconds should do it. Cumulative stress from the pump is the key, so don't worry that you're only a moving a fraction of your normal weights.

2 – The Alternating Forward Lunge

The lunge is a foundational exercise, but the most popular variation – the alternating forward lunge – is the most butchered. A rule of thumb is to never load (use weights) during a dysfunctional movement pattern. But many people don't have the ability to complete a single bodyweight lunge with proper mechanics. And in a society that views more as better, that shitty form becomes even more heinous when loads are introduced.

A lack of hip and core stability translates into valgus (collapsed) knee positions, increased degrees of anterior translation of the knee extending over the foot, and the use of momentum and compensation creating unstable shear forces through the spine, hips, and just about every other joint in the body. The smart thing to do is fix your form. And if you depend on the lunge to round out an epic leg day, there's a simple movement modification to help you keep lunging without the unwanted compressional stress on the knee cap.

A Better Exercise – Static Split Squat

The forward lunge is a dynamic movement meaning that the foot stepping ahead requires movement to step, complete the lunge, and return back to neutral. Any dynamic movement that's just begging for injury can be simplified into a static variation. The static split squat is a good replacement for the forward lunge until you earn the right to progress once again.

Place your feet in a split stance, hip width apart. If your position is sound, you'll be able to drop down to the floor in a half-kneeling position and your hips and knees will create 90-degree angles. From this position, stay on one leg in non-alternating fashion and complete sets of full-range split squats. This will target the same musculature of the dynamic forward lunge but keep compensation and poor technique to a minimum.

If you find yourself struggling to keep your balance, then adding a dynamic component isn't the right variation for you. Go inside a rack or up against a wall and monitor your balance with your fingertips, enhancing your balance each session, ultimately working your way back to free standing.

How to Keep the Alternating Lunge, If You Must

The reverse lunge will activate the posterior chain musculature significantly more than its forward counterpart. It will achieve a slightly (10-15 degree) higher front side hip flexion angle when the lunge is completed in split stance position.

This higher hip flexion angle will allow the rectus femoris (a quad muscle in your thigh) to be slightly slackened when the back foot is placed behind the front and when you're doing the eccentric portion of the lunge. Without the strain from this muscle, the patella is more likely to respond favorably to the training forces through the quads rather than the strain on non-contractile tissues such as the patellar ligaments and fascia on the front side of the knee.

By moving through the reverse variation of this exercise, you'll be able to train the quads and legs just as effectively as the forward version, minus the chronic stress and poor positions. And anyways, who doesn't need a little extra booty emphasis on leg day? That's a win-win.

3 – Running

If you're a runner, you're either one of two people: A natural born runner with impeccable gait mechanics, or a pretender who's slogged through just enough miles to call yourself a runner, but not enough to finally break your body.

If your goal is to stay fit and healthy for the long run, prioritizing road work at sustained mid level threshold outputs for hours on end isn't your fast track to fat-loss or body recomposition. But on the plus side, it may help you finally tap into that health insurance plan. Here's how to make some intelligent modifications to your training if and when you're ready to break up with running.

A Better Exercise – Incline Treadmill Walks

The intelligent movement modification for running is to... wait for it... stop running. Granted, going for a jog once or twice a month isn't going to kill your body. But adhering to a multiple-day-a-week running schedule at moderate intensity and mid-mileage is the norm, and something that's in need of modification if your goal is staying healthy.

Training your cardiovascular system effectively involves more options than just running. As long as the specific energy system is targeted properly through heart rates and oxygen thresholds, cardio is cardio and your body can't discern the difference. Even if you plan on taking part in one long steady-state run a week, you can supplement in a more joint-friendly cardiovascular activity another few days a week to match your cardio output and keep your levels of conditioning up. My top recommendation is incline treadmill walks.

Do them 2-3 days a week, and if you're dead-set on keeping your heart rate elevated at a sustained level, match your outputs on the runs with your systemic outputs on the walks. Just increase the speed and incline enough to reach those specific variables, minus the high impact rates associated with running.

How to Keep Running, If You Must

There's just something about running that captivates people both physically and mentally. So if you're not going to supplement incline walks into your cardio program a few days a week, at least vary your runs enough to avoid the stagnation and plateaus of training effects commonly associated with steady state cardio. This can be done through two different types of programming: traditional interval style runs, or sprints and Fartlek-style training:

You're familiar with intervals, where a faster running speed is completed for a duration followed by a slower speed to tap into heart rate variability and cardiovascular response. Likewise, Fartlek runs allow the variability in heart rate, but also the challenge of constant variances of speeds, inclines, and training variables to produce a more novel training stimulus compared to a steady state run.

Start off simply with the Fartlek runs, determining a specific time or distance for the run, and listen to your body. Challenge yourself with tempo runs, slower jogs, or periods of incline running if you're on a treadmill. Because it's randomized, every Fartlek run will be different. When it comes to improving the orthopedic response to a highly repetitive sport or activity such as running, the more variability in gait stride, speed, and ground reaction forces, the better.

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