Active and passive joint stability: the never-ending game of tug of war


Afbeeldingsresultaat voor knee joint

Ever wondered what keeps your joints from falling apart when you do a heavy movement?

Joint stability is something like a lot of things in life: you only miss it when it’s gone. But what exactly creates stability? In short there are 2 main factors playing a role: active stability and passive stability

Passive stability

Passive stability is created by mostly bones and ligaments. They help your body from not falling apart or doing things which make you say “eeeeewwwww” like hyperextending your knee. It is something we are all born with and unless we somehow lose it (like rupturing your ACL, breaking a bone, …) will help is keep stability in a joint.

Passive stability is mostly the same across individuals, but sometimes we have people who have greater mobility because of longer ligaments or different bone structure, which can allow them to for example hyperextend their knee. This can be a blessing in some situations (you are more flexible), but can be a curse in others: landing with hyperextended knees for example is not a good thing and can easily result in injury.

Afbeeldingsresultaat voor flexibility meme

Active stability

The second form consists of muscle contractions. Around every joint, the supporting muscles will exert forces on it. This constant pulling in different directions will make the joint more stable. Think of it as a battle of tug of war where the teams are perfectly equal.

Afbeeldingsresultaat voor tug of war

That said, what happens if the teams =(muscles) are not equally strong? Imbalances in pulling forces can create too high forces on certain parts of the joint and ligaments, which can lead to injuries.

So what does this mean I should do?

There is nothing we can do to change our passive stability (except not screwing it up in the first place). Active stability however can be trained. There are 2 factors which should be taken into consideration when looking at the risk of injury:

  • Maximal force possible: the stronger the muscle, the more force it can produce and therefor the more it can help your joint stabilize
  • Muscle (im)balances: this refers back to our tug of war analogy. Having equally strong surrounding muscles will ensure your pulling forces to be equal and minimize your risk of injury.

What exercises should I use for this?

This is why closed chain movements are usually superior to open chain isolation exercises. A closed chain movement means there is contact with the floor or another surface. This contact allows the body to use multiple muscles at once, which is exactly what we want. When we are talking about closes chain movements, we think of squats, lunges, step-ups, deadlifts, shoulder press, …

Open chain movements however equals no contact with the floor, which is usually the case with isolation exercises. Therefore, only muscles on 1 side will be working, which produces shear forces and can destabilize your joint. Think of a biceps curl, ham curl, triceps extension, … and most of the other machine exercises.

So I would firmly recommend you to use compound exercises. There is however a room for isolation work when you have a muscle which is severely lagging. In this case it might actually be better, since you don’t want to have unequal pulling forces in your closed chain movements.

Afbeeldingsresultaat voor squat

 

Now you know what makes your knee from falling apart, go work on your strength! Make sure the teams that are pulling the rope are equally strong, or one of them is bound to lose (and that means you lose too).