21. Leglocks - What are the differences between an ankle lock/achilles lock, heelhook, toehold, and kneebar (And is it true the ankle/achilles lock is just a pain submission)?
A great instructional resource to explain leglocks:
High Percentage Leglocks - Ankle Locks, Heel Hooks & Toeholds
Great articles:
Kneebar Leg lock Q & A from Grapple Arts
Breaking down the Ankle Lock - an analysis of the basic foot lock
Quick summary of each lock:
Ankle lock/achilles lock: Works by extending the toes downward while cranking up on the achilles tendon, right behind the heel. Can be applied from a variety of leg positions. The names "ankle lock" and "achilles lock" essentially mean the same leglock, but minor differences in how the lock is applied can change its effect more towards crushing the achilles tendon or hyper-extending the foot -- either can create the tap, and both are usually involved to some degree. NOTE: Contrary to common claims, this lock can easily break/damage the foot, and is absolutely not just a pain submission. It is, however, probably the safest leglock, because there is little or no twisting action applied to the knee -- unlike the heelhook, which looks very similar and uses a similar control position as the ankle lock. For this reason, the straight ankle lock is typically legal at blue belt and up in gi BJJ, and always legal in no-gi competition.
Heelhook: Looks very similar to ankle/achilles lock, but the heel is cupped over the arm rather than under it. The heel can be twisted either way, inside for a regular heelhook, outside for a reverse heelhook. The leg is twisted to finish, along with bridging back. Primarily attacks the knee and hip. A very dangerous submission that is always illegal in gi BJJ and in judo, but allowed in MMA and some no-gi tournaments. The reverse heelhook is probably the most devastating leglock of all, and can easily cause severe injury.
Toehold: The toes are grabbed with one hand, and the other arm grabs the wrist in a "figure 4" lock on the foot. The foot is then twisted back. Attacks the ankle and knee joints. Legal at brown belt and above in BJJ. A very versatile attack that can be used from many positions. Also a dangerous lock, due to the twisting force it creates on the knee joint.
Kneebar: Basically just like an armbar, but done to the leg. Requires good technique to finish, due to the great strength of the leg. Kneebar, as its name indicates, attacks the knee joint. It attacks an important joint, but because it does not use much twisting force, is usually thought to be somewhat less dangerous than heelhooks and toeholds. Usually legal in gi BJJ from purple on up.
Others: There is a dizzying variety of leglocks, but 99% of what actually finishes people in competition are the locks listed above. You may also encounter calf slicers, shin locks, Indian death locks, hip locks, banana splits, etcetera, but they are much less frequent, and primarily applied by leglock specialists.