The basic Muay Thai knee is called the stabbing knee, and it goes directly into the abdomen or sternum of your opponent. Drive the knee forward and back. One fluid movement. That's it.
But here's where most people get it wrong. They lift the leg first and THEN push the knee out. Two separate motions. Scott Sullivan is very clear about this — you do not want to lift and push. You want one fluid movement going straight to the body. The difference is the difference between a technique that lands and one that gets you hit with a jab on the way in.
The other detail that matters: don't throw it from directly in front of your opponent. Step to the side first, then deliver the knee. That slight angle change keeps you out of harm's way — you're not walking straight into their punches. You get a safer outside angle while still stabbing the knee into the body.
Extend your lead hand as you throw it. That hand does two things — it measures distance and it protects your face. Without it, you're wide open.
You can angle the knee or drive it straight. Both work. The important thing is the mechanics: step, extend the hand, drive the knee forward in one motion, recover.
This is the foundation for every other knee technique in Muay Thai. The flying knee, the clinch knee, the switch knee — they all build on this basic stabbing motion. Get this one right and the rest come naturally. Rush past it and you'll always have a hole in your game.
For more fundamentals, check out our complete Muay Thai for beginners guide. Get the full course in the Ultimate Muay Thai Training System.