Up Knee

Last updated: May 25, 2026

What is an up knee?

“Up knee” is informal MMA terminology for what striking coaches more often call a straight knee or front knee. The defining feature is direction. The front of the knee, leading with the kneecap or just above it, travels upward into the target. This sets it apart from curved knees and flying knees, where the trajectory and the body mechanics differ.

The up knee has roots in Muay Thai, where it is known as khao trong. MMA inherited the technique through striking coaches and fighters with Muay Thai backgrounds. It sits within a wider family of knee strikes that share the same weapon, the knee, but differ in trajectory and range, and in the situations where they fit.

Most often, the up knee shows up at close range. A fighter inside the clinch will use it to attack the body. A defender stuffing a takedown will use it to punish the head as the opponent ducks in. The same basic action carries across positions: drive the knee upward into whatever is in front of it.

How the up knee works

The mechanics combine leg drive with hip extension. The rear or lead leg comes up at the knee, and at the same moment, the hips push forward and upward. The foot points down as the knee rises, which lets the front of the knee strike the target cleanly.

Power comes mostly from the hip thrust rather than the leg lift. This is why coaches stress hip extension when teaching knee strikes.

Targets sit at chest height or above. The strike can land on the sternum, the solar plexus, or the floating ribs. The opponent’s posture matters: when their head is bent down in a clinch, the chin becomes the highest-value target. Wikipedia’s knee strike entry catalogues these same landing spots for the front knee.

A viewer can identify an up knee by the vertical motion of the leg and the absence of any twist or jump around it.

Up knee vs. flying knee vs. curved knee

The up knee is part of a wider knee strike family in MMA, and viewers often confuse it with two closely related techniques: the flying knee and the curved knee. The differences are mostly in trajectory and how power is generated.

Strike	Trajectory	Range	Typical position	Common target
Up knee	Upward, front of knee leading	Close to mid	Clinch, sprawl, top control	Body, sternum, chin
Flying knee	Upward with a jump	Mid to long	Open distance, charging in	Head, jaw
Curved knee	Horizontal, rotated from outside	Inside clinch	Tight clinch	Ribs, side of body

A flying knee shares the upward trajectory of an up knee, but the jumping motion separates them. A curved knee, by contrast, swings horizontally and is used at distances where the up knee cannot fit.

Where up knees show up in MMA

In an MMA fight, up knees most often emerge from the clinch. A fighter who controls the opponent’s head or neck, often with a double collar tie (sometimes called the Thai plum), can pull the head downward and drive a knee upward at the same time. That combined motion drives more force into the strike than a static target would allow.

Sprawl defence is another common setting. As the opponent ducks in low for a takedown, a defender who pushes the head down can fire a knee into the incoming face. The opponent’s own forward momentum carries them straight into the rising knee, which is one reason this technique can finish fights in seconds. Speak MMA’s article on illegal knees in MMA covers where the legal lines sit on these positions.

Up knees can also land from top positions on the ground, such as side control or north-south, depending on the ruleset. The same upward motion applies, just with gravity helping rather than working against the strike.

Are up knees legal in MMA?

Under the Unified Rules of MMA, an up knee to a standing opponent’s head or body is legal. Once that opponent becomes grounded, the strike to the head becomes illegal. The body remains a legal target in most positions.

The definition of “grounded” has shifted over time. At its 2024 annual conference, the Association of Boxing Commissions updated the rule so that a fighter is now considered grounded only when a body part other than the hands or feet touches the canvas. A simple hand on the mat no longer counts. CBS Sports reported the change after the ABC vote.

ONE Championship operates under a separate ruleset, the Global Martial Arts Rule Set for Competition, and allows knees to grounded opponents in many positions. This split is one of the more visible rule differences between the major MMA promotions today.

Frequently Asked Questions

What’s the difference between an up knee and a straight knee?

They are essentially the same technique. “Up knee” is informal terminology used by commentators and fans, while striking coaches more often call it a straight knee or front knee. Muay Thai uses the name khao trong.

Is an up knee the same as a flying knee?

No. A flying knee involves a jumping motion. The standard up knee is thrown with at least one foot on the ground throughout the strike. The trajectory looks similar, but the mechanics differ.

Can a fighter throw up knees from the ground?

From top positions such as side control or north-south, an up knee to the body is legal under most rulesets. Knees to the head of a grounded opponent are illegal under the Unified Rules but legal in ONE Championship.

What target does an up knee usually hit?

Up knees commonly land on the sternum and the solar plexus. The ribs and the chin come into range too, especially when the opponent’s posture is broken in a clinch, and the head drops.

Why are up knees so effective in the clinch?

The clinch lets the attacker pull the opponent’s head down while driving the knee up. The two motions meet in the middle, which adds power compared to a knee thrown at a static target.

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Sources

1. Wikipedia. “Knee (strike).” Accessed May 2026.
2. Evolve Vacation. “The Different Types Of Knees In Muay Thai.” Accessed May 2026.
3. Evolve University. “The Ultimate Guide To Muay Thai Knees.” Accessed May 2026.
4. Speak MMA. “What Is An Illegal Knee In MMA?” Accessed May 2026.
5. CBS Sports. “Commission removes 12-6 elbows from Unified MMA rules, updates grounded opponent rule.” Accessed May 2026.
6. Heavy.com. “WATCH: Explaining the New MMA Rules That Debuted at UFC Edmonton.” Accessed May 2026.

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