What is Knee Flexion and Extension? - Muscles Used & 10 Exercises

What is Knee Flexion and Extension? - Muscles Used & 10 Exercises

knee_flexionYou use knee flexion and extension every day.

Every time you sit down and stand up, your knee goes through flexion and extension. It is a basic part of human movement.

As a fitness coach, it’s essential that you understand human movement. It will help you write better exercise programs and explain your rationale to your clients.

To help you write better exercise programs, let’s look at what knee flexion and extension are, their uses in everyday life, and exercises to strengthen them. 

What is Knee Flexion and Extension?


Knee flexion is a movement that decreases the angle between your thigh and your shin. Think curling your heel to your glutes. 

Knee extension is a movement that increases the angle between your thigh and your shin. Think kicking your leg straight. 

Both of them take place on the sagittal plane and occur both unilaterally and bilaterally. The squat and lunge movement patterns both use knee flexion and extension. Some knee flexion and extension may occur in certain bend pattern exercises too, such as the bottom of a conventional deadlift.

The Muscles Used in Knee Flexion and Extension

The main muscles used in knee flexion and extension are the quadriceps and hamstrings.

The quadriceps are on the top of your thigh and responsible for knee extension, or straightening your leg.

The hamstrings are on the backside of your thigh and are in charge of flexion, or curling your leg to your glute.

Flexion and Extension in Everyday Life

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You use both of these movements throughout your life. Every time you go for a walk, climb the stairs, sit down, go for a hike, duck under a branch, or pick something up off the ground, your knee goes through flexion and extension.

Thus, training these knee movements has a direct carryover to everyday life. As the muscles in the movement pattern get stronger, the movement becomes more efficient and enduring.

Here are our ten favorite exercises to train knee flexion and extension.

10 Different Knee Flexion and Extension Exercises

A note of caution, every individual possesses a different range of motion and motor control and these exercises may or may not be ideal for them. Assess your client’s ability before prescribing any of these exercises, and when in doubt, refer out. Learn our method for onboarding and assessing new clients here.

1) The Goblet Squat

Start the Goblet Squat standing with hips as wide as your shoulders with the weight in the goblet position. Then hinge at the hips and flex the knees to squat down. Drive with your glutes and return to the standing position. This is one repetition.

2) The Dumbbell Front Rack Cyclist Squat

Start the Dumbbell Front Rack Cyclist Squat standing with your heels elevated on a riser and a dumbbell in each hand. Then, hold a dumbbell in each hand and bring them up to the front rack position. Squat down to the bottom of a squat position and then drive back up to standing.

We love the cyclist squat because plates under the heels mean there can be more knee flexion.

3) Box Squat

Start the Box Squat in a standing position with the bar placed on your traps. Break at the hips and lower until you are in a fully seated position on a bench, driving back to a full standing position.

4) Split Squat

Start the Split Squat in the split position, bending the front knee into a lunge until the thigh is parallel to the ground and the back knee lightly touching the floor. Drive back up to stand.

5) Dumbbell Lunge

Start the Dumbbell Lunge standing with a dumbbell in each hand. Then step forward with one foot. Keep your knees over your toes with the front foot and lower your back knee to the ground. Then drive back up and bring the front foot back to the starting position. 

6) Reverse Lunge

Start the Reverse Lunge with feet hip-width apart, take a step backward with the right foot and then slowly bend both knees until the back knee lightly touches the floor, returning to the start position, then take a step backward with the left foot and bend both knees until the back knee is just above the floor, returning to the start position.

7) Dumbbell RNT Split Squat

Start the Dumbbell RNT Split Squat in the split stance position while holding two dumbbells down by your sides, with a band wrapped around your distal knee. Slowly lower in a vertical motion until the back knee lightly touches the ground, then raise back to the starting position.

8) Dumbbell Step-Up

Start the dumbbell step up standing in front of a box holding a dumbbell in both hands. Step up one leg at a time until both feet are on top of the box. Then step back down and repeat, leading with the opposite leg.

9) Pistol Squat

Start the Pistol Squat in the standing position with your feet shoulder-width apart. Balance on one leg, extend the opposite leg out in front of your body. Break at the hips and squat until the hip is below your knee and return to the starting position all while keeping one leg extended.

10) Poor Man’s Leg Extension

Start the Poor Man's Leg Extension on both knees. Then lower yourself backwards until your glutes almost touch your heels. Then, use your quads to pull yourself back up to the straight-up kneeling position. 

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