Doctor That Trains BJJ Answers Question: ‘Is Knee Reaping Dangerous?’

Doctor That Trains BJJ Answers Question: ‘Is Knee Reaping Dangerous?’

Leg/knee reaping when doing a foot lock is a very controversial topic in BJJ today. Some say that the act of reaping the leg is dangerous and can injure the knee, whilst others such as Ryan Hall say that it is no more dangerous and that BJJ players are overreacting.

The leg reap according the IBJJF rulebook is:

“When one of the athletes places his thigh behind the leg of his opponent and passes his calf on top of the opponent’s body above the knee, placing his foot beyond the vertical midline of the opponent’s body and applying pressure on his opponent’s knee from the outside.

This video explains the exact definition of leg reaping according to IBJJF:


Professor Gustavo Gasperin and Dr. Mike Piekarski, DPT analyze the dreaded position and give safety tips to avoid potential injuries.

Dr Piekarski trains Jiu-Jitsu and his analysis of reaping is that it is only dangerous if you resist the torque of the reap by going against it. He says that if go with the flow of the technique and then learn how to defend the foot lock on time, then there should not be any risk of injury.

Watch here:



BJJEE interviewed Samuel Sanvicente who is a BJJ black belt instructor at Groundfighters in Hamburg, Germany, IBJJF and an Osteopath and asked him about his opinion regarding the controversial knee reaping rule:

“I train BJJ for more than 12 years and I have worked as Massage therapist and osteopath together with Orthopedic Surgeons for about 15 years. In this time I saw a lot of grapplers and MMA fighters suffering knee injuries because of reaping the knee. When I started with BJJ we were always training with reaping of the knee and heel hooks. Personally I don’t have any problem with this position and I would fight with allowed heel hooks and reaping the knee, but I think that the IBJJF did the right thing in forbidding this move.


Samuel Sanvicente

Samuel Sanvicente


The knee, due to its design and articulation has just a single sense movement, flexion-extension, although in an accessory way it possesses a second freedom sense, rotation on the leg longitudinal axis which appears just when the knee has been flexed but this is a very short move and it is one of the reasons why reaping the knee is so dangerous.

What happens in the reaping the knee position?

Normally (not always on the case of the hip flexion), when we are doing this position the hip and the knee going in a position of flexion and internal rotation and the knee joint do also a little (passive) move of adduction, bringing some structures of the knee joint to the point of maximal tension. These moves combined, with the internal rotation and adduction of the knee) may cause injuries on the MCL (medial collateral ligament), ACL (anterior cruciate ligament), PCL (posterior cruciate ligament) less common but also possible, medial and lateral meniscus and articular capsule, between another’s structures and depending of the magnitude of the force and angle of the joint at this moment.

The degree of the flexion of hip and knee can be different in every situation and this fact can cause different injuries, but now we will focus on the moves with a hip flexion of 90 degrees.

The internal rotation of the hip is about 30 degrees and the external about 60 degrees (it depends of the person).

When you do a reaping the knee, the internal rotation movement of the hip stops very early and because the hip is a very strong joint and the knee is the next weaker joint between the point A (Hip) and B (Foot-distal part of the shin), on the case that point A and B are blocked, as it often happens, the knee joint will receive a lot of pressure and the risk of suffering knee damage in this position is very high.

Also as referee of the IBJJF I saw some knee injuries because of reaping the knee and in the short time as referee assistant in Naga I’ve see too many knee injuries because of knee reaps, most of the times in lower belts.

Reaping the knee for black belts? Well, I’m sure that we would see a lot of athletes suffer from Knee injuries and this wouldn’t be good for the sport. For lower belts in my opinion this is a very bad idea. But this is only my personal point of view. My students learn heel hooks as purple belts and sometimes they are allowed to use it, but training isn’t competition.”

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