What Flexion and Extension Means for Your Workouts

TRAINING EFFECTIVELY MEANS training smart. There are plenty of gym-centric terms floating around the fitness zeitgeist that won’t necessarily help you become stronger or build more muscle, especially if you’re just getting started in the weight room. Most of the time, training smart means understanding the basics—so it’s worth making time to learn about concepts that can help you understand why you should move in certain ways in order to achieve certain outcomes. Two of those terms include flexion and extension.

Many exercises can be broken into two parts: The portion where you are shortening the angle of the joint (flexion), and the portion where you are lengthening the angle of the joint (extension). Understanding both will teach you how to calibrate your efforts so you can achieve your goals even more quickly.

What Is Flexion vs. Extension The difference between flexion and extension comes down to joint angle.

FlexionFlexion makes the joint angle smaller, bringing two body parts closer together. Examples of flexion include:

Biceps curl Leg curl SitupsExtensionExtension makes the joint angle larger, moving two body parts farther away from each other. Examples of extension include:

Triceps kickbacksLeg extensionsBack extensions If you’re thinking it sounds like some exercises include both flexion and extension, you’re not wrong. When you drop down into a squat, for example, you flex your hips and knees, and when you drive out of it, you extend them. But while most exercises incorporate flexion and extension, nearly all of them focus on one aspect or the other.

Let’s dial in on this concept to make it more clear: when you squat, the focus is on driving out of the hole into a standing position. That puts the main point of focus extension. The biceps curl, on the other hand, emphasizes bending the elbow to bring the forearm closer to the upper arm, making it an extension-focused movement.

If you’re ever unsure, keep this simple maxim in mind: flexion is forward and extension is backward. The exceptions to that rule are exercises that involve bending the knee (e.g., hamstring curl). For those, default to rule number one: if the exercise brings two body parts closer together, it’s flexion; if it does the opposite, it’s extension.

How to Incorporate Flexion and Extension Into Your WorkoutsFlexion and extension are simple concepts, but keeping them in mind as you program your training plan can have a powerful impact on your results.

Step one: Make sure that you include a roughly equal number of flexion and extension moves in your routine. That will help ensure you build balanced strength and muscle while minimizing your risk of injury. Performing both the biceps curl (flexion) and triceps kickback (extension) each week will strengthen both sides of your arms, for example. (For that particular pairing, you’ll also set yourself up to work in a superset structure that allows you to double up without needing to rest.)

But here’s something else to consider: You can also use the principles of flexion and extension to double down on the same muscle group and amplify your gains. The key is to emphasize the eccentric (lowering) phase of a handful of exercises each week—by, say, taking as long to lower the dumbbell during a biceps curl. In so doing, you’ll increase each muscle group’s time under tension—a key growth stimulus. The result: more strength and power in everything you do.

Trevor Thieme is a Los Angeles-based writer and strength coach, and a former fitness editor at Men’s Health. When not helping others get in shape, he splits his time between surfing, skiing, hiking, mountain biking, and trying to keep up with his 10-year-old daughter.

Cori Ritchey, C.S.C.S., is an Associate Health & Fitness Editor at Men’s Health, a certified strength and condition coach, and group fitness instructor. She reports on topics regarding health, nutrition, mental health, fitness, sex, and relationships. You can find more of her work in HealthCentral, Livestrong, Self, and others.