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

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