Flexion and Extension in Bodybuilding

By: Jeremy Fox, CNC, CPTPublished: July 7, 2023

When we first start going to the gym, many of us begin lifting weights without much understanding of how our bodies work. While it’s better than nothing, haphazard training is definitely not the safest or most effective approach.

As we progress, we gain knowledge of body mechanics and become familiar with terms like flexion and extension. Understanding these concepts thoroughly can take our training from average to elite.

To help you optimize your resistance training for building muscle and strength, I have created a definitive guide on flexion and extension. Keep reading to learn how to use your anatomy to improve your training!

Flexion and Extension Bodybuilding

What Are Flexion and Extension?

Anatomical terms such as flexion and extension describe the angle between two body parts and the movement around particular joints.

For instance, flexion of the elbow joint involves bringing your forearm closer to your upper arm, reducing the angle. Conversely, elbow extension involves straightening your arm and increasing the angle.

This same terminology is applied to many other joints in the body, including the knees, hips, and shoulders.

Flexion and Extension Example

Application in Resistance Training

To move your body, you need skeletal muscles. These muscles pull on the framework of levers that makes up your skeleton, creating movement.

When you contract a muscle that’s attached to two bones, it pulls them closer together, which is called flexion. Conversely, when you contract the opposite muscles, it pulls the same bones further apart, which is called extension.

For instance, when you flex your bicep, your forearm bones move closer to the humorous, while contracting your tricep moves the arm bones further apart.

Resistance training involves pulling these levers against a load to make your muscles bigger and stronger. If you understand flexion and extension, you can effectively design resistance training programs targeting specific muscle groups.

Flexion and Extension by Joint

In this section, we will discuss the definitions of flexion and extension in different joints of the body. Additionally, I will provide examples of exercises that demonstrate the difference between flexion vs extension for joints such as the knees, hips, shoulders, elbows, and more.

Table 1. Primary Muscles Involved in Flexion and Extension by Joint
  Flexion Extension
Knee Quadriceps Hamstrings
Hip Hip Flexors Gluteus
Shoulder Anterior Deltoid Latissimus Dorsi
Elbow Biceps Triceps

Knee Flexion and Extension

The knee joint operates similarly to the elbow joint, functioning as a hinge. Like your arm, your leg can perform flexion and extension movements.

When you contract the hamstrings, your knee performs a flexion movement. And exercises designed to isolate this muscle group are called leg curls, like bicep curls.

On the other hand, when you contract the quadriceps, your knee performs an extension movement. This is why the equipment used to isolate the quads is called a leg extension machine.

Knee Flexion and Extension

Knee Flexion Exercises:

  • Hamstring Curls

Knee Extension Exercises:

Hip Flexion and Extension

The hip joint is unique as it enables movement in various directions through its ball and socket structure. Unlike the knee, the hip can also perform abduction and adduction, so it’s important to distinguish the movements.

When the frontal hip flexor muscles contract, the thigh moves forward, resulting in hip flexion. Leg lifts are an example exercise that targets hip flexion.

On the other hand, the gluteus muscles in the backside contract during hip extension, causing the hips to straighten. The hip thrust is an exercise that focuses on hip extension.

Knee Flexion and Extension

Hip Flexion Exercises:

  • Leg Lifts

Hip Extension Exercises:

Shoulder Flexion and Extension

The shoulder joint is another ball and socket joint capable of moving in multiple directions, much like the hip joint. Therefore, shoulder flexion and extension movements are similar to the hips.

Raising your arms straight out to the front is an example of shoulder flexion, and this movement can be exercised through front raises.

Pulling your arms down and behind your torso is an example of shoulder extension, controlled by the latissimus dorsi (lats) more than the deltoids.

Shoulder Flexion and Extension

Shoulder Flexion Exercises:

Shoulder Extension Exercises:

Elbow Flexion and Extension

As we previously discussed, the elbow functions as a hinge joint where the bicep performs flexion, and the tricep performs extension.

To exercise elbow flexion, one can perform various types of bicep curls. On the other hand, elbow extension exercises usually involve tricep pushdown or pressdown movements.

Elbow Flexion Exercises:

Elbow Extension Exercises:

Other Joints

The joints of the wrist, ankles, and spine can also undergo flexion and extension. The wrist and ankles are sliding joints, whereas the spinal vertebrae connect through facet joints.

To perform wrist flexion, you pull your palm toward the bottom of your forearm. Wrist extension involves pulling the back of your hand toward the top of your forearm. Each movement is controlled by the wrist flexor and extensor muscles.

Ankle flexion, or dorsiflexion, requires the tibialis muscles to pull your toes toward your shin. Conversely, ankle extension, aka plantar flexion, involves pulling your toes towards the floor, as in a calf raise.

Lastly, spinal flexion involves pulling your torso forward, as in an abdominal crunch. And for spinal extension, you pull your spine to the rear like doing a hyperextension exercise.

Flexion and Extension of Ankle Joint

Flexion and Extension In Compound Movements

So far, we have mainly talked about flexion and extension in relation to single-joint movements. However, things become more complex when we look at compound exercises that involve two or more joints.

For instance, let’s consider the traditional barbell back squat. During squats, you bend at the hips, knees, and ankles – all three joints undergo some degree of flexion and extension.

Furthermore, individual body proportions, bar placement, and stance width can impact joint angles during the squat exercise. Although we can’t alter our body proportions, we can modify the exercise to achieve our desired training outcome.

To illustrate, a narrow stance squat generally increases knee flexion while reducing hip flexion, resulting in greater quad activation during the concentric phase. Conversely, a wide stance results in more hip and glute activation.

In addition, placing the bar higher on your shoulders results in a more upright posture with less hip flexion and greater knee flexion. This, in turn, activates the quads more during extension.

Conversely, utilizing a low bar position results in more hip flexion and less knee flexion, which is advantageous for activating the glutes and hamstrings during squats

Finally, elevating the heels during squats reduces ankle dorsiflexion while increasing knee flexion. This small adjustment can allow people with limited ankle mobility to squat deeper and maintain better form.

These are just a few instances where we can utilize our understanding of extension and flexion to customize exercises for our workout objectives. Similar principles can be applied to both compound and isolation movements.

workouts mobile

Custom Nutrition & Workout Plan

Get a personalized meal plan built to fit your body and lifestyle. Including a custom workout routine designed around your fitness goals.

With your custom plan, you will finally be able to burn fat, build muscle, and transform your body. All this for just $19.99!

Click here to choose your plan.

More Exercise & Workout Guides

Hopefully, this information has provided you with a practical knowledge of exercise physiology without getting too bogged down in scientific terminology!

If you enjoyed this article, I have several more that I think you will find interesting.

Supination vs Pronation: Why Grip Matters

Flat Foot vs Heel Elevated Squat Kinematics

Flat Bench Press vs Incline Bench Press for Chest

Arnold Press vs Shoulder Press Muscle Activation

Wide Grip vs Close Grip Lat Pulldown Differences

If you’ve had enough anatomy and physiology for one day, feel free to browse my other fitness-related content below. You’ll find free information on nutrition, supplements, and workouts.

Share with your community and get the conversation started!

By |July 7, 2023|Bodybuilding|Comments Off on Leveraging Flexion and Extension In Bodybuilding Exercises
Go to Top