Flexion

Flexion - Closing the joint angle

Definition

Flexion is an anatomical movement that decreases the angle between two body segments at a joint. It is the opposite of extension, which increases that angle.

💡 Memory trick: flexion = "folding" (think "flex" your bicep — you fold the elbow). Extension = "extending".

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Examples of flexion

• Elbow flexion: bicep curl, the bicep contracts
• Knee flexion: leg curl, hamstrings activate
• Hip flexion: lifting your knee toward your chest
• Spinal flexion: rounding forward (sit-up, crunch)
• Wrist flexion: bending hand toward inner forearm

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Main flexor muscles

Joint	Main flexors
Elbow	Biceps brachii, brachialis, brachioradialis
Knee	Hamstrings (biceps femoris, semitendinosus, semimembranosus)
Hip	Iliopsoas, rectus femoris
Spine	Rectus abdominis (abs), obliques
Shoulder	Anterior deltoid, pectoralis major

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Best exercises for flexors

Elbow flexion (biceps)

• ✅ Barbell curl, hammer curl, preacher curl, chin-up

Knee flexion (hamstrings)

• ✅ Leg curl, Nordic curl, glute-ham raise

Hip flexion

• ✅ Hanging leg raise, knee raise, sit-up

Spinal flexion (abs)

• ✅ Crunch, cable crunch, sit-up

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The case of hip flexion

Hip flexors (especially the iliopsoas) are chronically tight in most people due to extended sitting. Consequences:

• ❌ Lower back pain
• ❌ Forward pelvic tilt
• ❌ Glutes "shut off" because hip flexors dominate
• ❌ Reduced sprint and squat performance

Solution: regular stretching of hip flexors (low lunge, pigeon, etc.).

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Common mistakes

• ❌ Confusing flexion (close angle) with extension (open angle)
• ❌ Working only flexors, ignoring extensors (muscle imbalance)
• ❌ Sitting all day = tight hip flexors
• ❌ Excessive crunches without extension work (rounded back)

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Key takeaways

Flexion = closing the joint angle. Essential for grip, posture, and movement. Always balance with proper extensor work to avoid muscular imbalances. Stretch hip flexors regularly if you sit for long hours.