Flexion

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".

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

Main flexor muscles

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

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.).

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)

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.