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Leg Extension

Isolated quad burn — direct quadriceps work for building size and addressing weaknesses

⚡ Quick Reference​

AspectDetails
PatternIsolation
Primary MusclesQuads
EquipmentLeg Extension Machine
Difficulty⭐ Beginner
Priority🟠 Common

🎯 Setup​

Machine Adjustment​

  1. Seat back: Adjust so knee aligns with machine pivot
  2. Pad position: Just above ankles on lower shins
  3. Foot position: Toes pointed straight or slightly out
  4. Hand position: Grip handles on sides of seat
Proper Alignment

The machine's pivot point should align with your knee joint. Poor alignment creates inefficient leverage and potential knee stress.

🔄 Execution​

The Movement​

What's happening: Straightening legs against resistance

  1. Extend knees to raise pad
  2. Full extension at top
  3. Squeeze quads at lockout
  4. Breathing: Exhale during extension

Tempo: 1-2 seconds

Key Cues​

Primary Cues
  • "Squeeze at the top" — maximize quad contraction
  • "Control the descent" — don't let weight drop
  • "Full extension" — straighten legs completely

💪 Muscles Worked​

Primary Movers​

MuscleActionActivation
QuadricepsKnee extension██████████ 100%
Pure Isolation

Leg extensions are one of the few exercises that isolate the quadriceps almost completely. All four quad muscles (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) are heavily involved.

⚠️ Common Mistakes​

MistakeWhat HappensWhy It's BadFix
Too much weightUsing momentum, swingingPoor quad isolation, knee stressReduce weight, control it
Not full extensionStopping short of lockoutIncomplete quad contractionExtend fully, squeeze
Dropping weightLetting weight fallMissing eccentric workControl descent 2-3s
Lifting hips off seatUsing body EnglishNot isolating quadsLighter weight, stay seated
Toes pointing downPlantarflexionCalf involvementToes neutral or up
Knee Stress

While effective, leg extensions create shear force on the knee. Use controlled tempos and appropriate weight. If knee pain occurs, substitute with squats or leg press.

🔀 Variations​

Common Variations​

  • Standard execution
  • Can handle more weight
  • Typical training method

📊 Programming​

Rep Ranges by Goal​

GoalSetsRepsRestLoad
Hypertrophy3-410-1560-90sModerate
Endurance2-315-20+45-60sLight
Strength3-48-1290sHeavier

Workout Placement​

  • After compound movements — squats, leg press
  • End of leg workout — finishing quad work
  • Isolation focus — when targeting quad development
Programming Note

Leg extensions are best used as accessory work after compound movements like squats. They're excellent for adding volume without systemic fatigue.

🔄 Alternatives & Progressions​

Alternatives​

ExerciseWhen to UseLink
Leg PressNeed compound movement
Split SquatFunctional alternative
Terminal Knee Extension (TKE)Rehab/prehab

Progressions​

ExerciseWhen Ready
Single-Leg ExtensionMaster bilateral
Pause at topIncrease difficulty
Tempo workBuild control

🛡️ Safety & Contraindications​

Who Should Be Careful​

ConditionRiskModification
Patellar tendonitisIncreased stressAvoid or use very light
ACL injury historyShear forcesUse leg press instead
Knee painMay aggravateStop if painful
Stop If
  • Knee pain (not muscle burn)
  • Grinding or clicking with pain
  • Swelling after training

🦴 Joints Involved​

JointMovementROM
KneeExtension90-0° (flexed to straight)

Joint Considerations​

  • Single-joint exercise - only the knee moves
  • Open kinetic chain - foot moves freely (not fixed)
  • Shear force - creates anterior tibial translation; generally safe but be cautious with ACL history
ACL Consideration

Open chain knee extension creates anterior shear force on the tibia. While not harmful for healthy knees, those with ACL injuries or repairs should consult their physio before including this exercise.

❓ Common Questions​

Are leg extensions bad for your knees? Not inherently. They're used in physical therapy for knee rehab. However, very heavy loads with poor control can stress the joint. Use moderate weight and controlled tempos.

Can leg extensions build big quads? Yes, they're excellent for quad hypertrophy because they isolate the muscle group. Combine with compound movements like squats for best results.

Should I do leg extensions before or after squats? After. Compounds first (squats, leg press), isolation last (leg extensions). Pre-exhausting with extensions can compromise your squat performance.

Single leg or both legs? Both work. Single leg is great for fixing imbalances. Bilateral allows more total volume. Use both in your training.

Full extension or stop short? Full extension is fine and provides the best contraction. Just don't hyperextend or slam into lockout.

📚 Sources​

  • Escamilla, R. F. (1998). Knee biomechanics of the dynamic squat exercise. Medicine & Science in Sports & Exercise
  • Signorile, J. F., et al. (1994). Effect of foot position on the electromyographical activity of the superficial quadriceps muscles during the parallel squat and knee extension. Journal of Strength and Conditioning Research
  • Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research
For Mo

When to recommend this exercise:

  • User wants to build quad size
  • As accessory after squats
  • User has quad weakness
  • Bodybuilding/hypertrophy goals

Who should NOT do this exercise:

  • Knee pain or injury → Suggest Leg Press
  • Patellar tendonitis → Avoid
  • Prefer functional training → Use Split Squats

Key coaching cues:

  1. "Squeeze quads hard at the top"
  2. "Control the weight down, don't let it drop"
  3. "Full extension on every rep"

Programming guidance:

  • Place after compound leg exercises
  • Typical: 3 sets of 10-15 reps
  • Rest: 60-90 seconds
  • Use as accessory/finisher

Last updated: December 2024