Are Leg Extensions Bad for Your Knees? The Truth About Quad Growth, ACL Stress, and Knee Health

The Knee Extension Controversy

When I started as a certified trainer, experienced colleagues warned against leg extensions: “Bad for your knees,” or “It puts your knee joint at risk.” As a newcomer, I accepted this advice unquestioningly. For years, leg extensions became public enemy No. 1 for knee safety in my training philosophy. You’ve likely heard similar warnings:

• “Don’t do it—they’ll shred your patella”
• “That machine’s dangerous, just squat instead”

This belief has solidified into a persistent gym myth, potentially robbing lifters of an effective tool for quad development, strength building, and post-rehab recovery. After strength coach Nick Tumminello addressed this issue, we must ask: Are leg extensions knee-savers or knee-destroyers?

We’ll resolve this leg-day dilemma by examining the myth’s origins, biomechanics, and how to safely build teardrop quads with extensions.

Origins of the “D

Recommended Products:

• 

  Type Zero Ultra Clean Vegan BCAA Powder + Electrolytes (Hawaiian Punch | 6G) 2:1:1 Sugar-Free/No Sucralose BCAAs Amino Acids Supplement for Women/Men – Best BCAA Vegan Amino Acids After Workout Drink

  $24.95 Buy Now
• 

  Creatine Monohydrate Gummies for Strength & Athletic Performance – 5g Creatine Per Serving – Creatine Chews to Build Muscle, Increase Performance & Improve Post Workout Recovery – 120 Gummies (2-pack)

  $24.95 Buy Now
• 

  Nutrex Research EAA Hydration | EAAs + BCAA Powder | Muscle Recovery, Strength, Muscle Building, Endurance | 8G Essential Amino Acids + Electrolytes | 30 Servings (Fruit Punch)

  $27.99 Buy Now