Leg Extension Machine Substitutions. Plus some alternative options that target similar muscle groups!
1. Banded Leg Extension (use a hip band along with a regular band)
2. Quadruped Banded Knee Extension
3. Reverse Nordic
4. Sissy Squat (Unsupported if you're a ninja 🥷—no pressure!)
While you won't get the exact same stimulus as a machine, these options will still get your quads on 🔥!