SPEND ENOUGH TIME in the gym (or consume enough fitness-related content online), and you’re sure to encounter plenty of physiology terms. If you’re not a trainer yourself or you never took any type of anatomy or kinesiology course in school, that terminology can get confusing fast. Two terms that come up often when it comes to movement are flexion and extension.
Understanding concepts like flexion versus extension can help you better understand the purpose of your workouts, ultimately leading you to better performance. Whether you’re trying to increase athleticism, boost functional strength, or simply move better in and out of the gym, educating yourself on these topics will help you better tailor your training plan to your specific needs.
What Is Flexion vs. Extension
The difference between flexion and extension comes down to joint angle.
Flexion
Flexion makes the joint angle smaller, bringing two body parts closer together. Examples of flexion include:
- Biceps curl
- Leg curl
- Situps
Extension
Extension makes the joint angle larger, moving two body parts farther away from each other. Examples of extension include:
- Triceps kickbacks
- Leg extensions
- Back 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 Workouts
Flexion 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.
This is Your Quick Training Tip, a chance to learn how to work smarter in just a few moments so you can get right to your workout.
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