Understanding Tissue load

What is tissue load?  We hear this term thrown out by fitness and medical professionals alike.  But to many of you, this may not mean much.

So how can we take this boring, complicated topic, and make it useful to you?

Think of tissue load as how much force is being applied to an area.  Let’s take running as an example. With every step the forces, or load, acting on the body is roughly 3 times your body weight. This helps give us some insight into how we should be training our body so we can absorb the imposed impact.

Physical stress (load) is a composite value. Meaning that it is not just the magnitude of the forces that act on the body, but the time (how long you spend in a position, how many reps are performed etc…), rate, and direction the forces are applied as well.

Let’s think about how the application of physical stress to the body will cause our tissues to adapt in a number of predictable ways.

  1. If too little stress is applied, atrophy of the tissue happens.

  2. If just enough stress is applied, your body will be in a state of homeostasis.

  3. If you apply a stress that exceeds the maintenance range, what we term overload, hypertrophy or adaptation will happen.

  4. If there the forces acting on the body exceed the capabilities of the tissue, injury happens.

Based on these four principles, we can modify the amount of stress or load to create the adaptation we want.

Let’s look at this concept from a rehabilitation stand point.

When we get injured, our body goes into protective mode. Our body purposely decreases its threshold for pain to prevent us from using that part of our body.  What this means is that it takes much less load to cause pain and impede healing.

Let’s take an ankle sprain for example.  Prior to the sprain you were probably able to run, jump, and do anything your heart desired with no second thoughts.  After the sprain you are barely able to walk without limping in pain. In this case, the stress of simply walking is enough to exceed the tissues capacity and decrease the healing response.

The solution becomes removing the painful stimulus, and start challenging the tissue in a non-painful manner to help improve its force bearing capacities.  We are aiming to train our ankle with the overload principle above, but instead of looking for hypertrophy, we are looking to strengthen the tissue back to its original levels.

Let’s change directions a bit and use some examples of how load on the body can cause injury.

  1. A large magnitude force (getting struck by a car) gets placed on the body causing injury.

  2. A moderate magnitude force (lifting too heavy of a weight) applied many times causing injury.

  3. A low magnitude force (gravity acting on the body while sitting) applied for long duration (8 hours a day for 15 years) causing injury.

Not only do these forces add to each other, but stress from other areas of our life can contribute as well.  One thing that is becoming clear to us is that when your body perceives all the stress acting on the body (mechanical or not) as being too much for the body to handle, pain occurs.

So if we want to mitigate your injury risk, we can use this model to help us determine what is needed.  Obviously, we can’t do much about large magnitude forces (unless we put you in a protective bubble) getting struck by a car will cause tissue damage.

But when it comes to moderate and low magnitude forces, we can reduce the composite effects of mechanical loading.

Let’s take sitting 8 hours a day for example.

We can reduce the time component of stress by getting out of our chair periodically or changing positions.  This will give the tissues under constant tension a chance to recover.

On top of that, making sure that we move our body daily throughout it’s full range of motion will allow us to maintain our mobility levels, helping us to decrease our chances of becoming stiff over time.

If we also add strength to the equation, we have tissues that are more tolerable to mechanical load, and therefore, can either handle a larger magnitude load or handle a lower magnitude load for a longer period of time.

At the end of the day, regardless of what the literature states, it is never a bad idea to move more often and improve our movement patterns and strength levels.

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