The Laws of Fitness: SAID Principle

When it comes to fitness there are very few things that are set in stone.  There are so many techniques, movements, and varieties of methods. It can be argued that some may be better than others but to some extent they may all hold some value. Our bodies are wonderous devices capable of far exceeding the limits that we believe them to have. So when it comes to training and preparing our bodies, there may not be a wrong or right way, but there are things that we do know to be true and are the standing concepts with which all of this running around, lifting weights, biking, running, and pure simple hours of sweat are based on.

That being the case there are several “laws” that we do know exist and operate with out fail. The first is known as the SAID Principle. For the sake of this conversation we will acknowledge it as being a “law”.  The SAID Principle is “Specific Adaptation to Imposed Demands”.  In simple terms our bodies get better at what we make them do.

Sounds simple enough. If I want to do more push-ups, then I need to do more push-ups.  Or running, or whatever your activity is.  When I apply stress to my body in the form of physical resistance, power output or even speed, it creates a stimulus for my body. This stimulus can be compared to your body being given a need to get better. By asking more of our bodies than they are immediately prepared to give our body determines that a response must be made to be prepared for the next time this task is experienced again.


This stimulus and response results in an adaptation. This adaptation could be in the form of increased muscle density or size, it could be the coating of neurons with more myelin to improve our muscle control, it could also be change in the lungs and circulatory system to improve out ability to transport blood and oxygen.

One thing that we also have to look at is the elements of Specific and Imposed, not just the adaptation to demands. Our bodies only get better at what we ask it to do. If all I ever do in my workout is aerobics, then i have never given my body a need to lift heavier. Similarly, doing bicep curls every day is not going to help my squat. My arms might get bigger and stronger, but that is because that is the specific demand being imposed.

If we apply the same stress over and over again, our body will adapt but eventually that level of stress will no longer promote adaptation. In order to continue to adapt we have to increase the demand. This could be in several different forms.

  1. Simple movements to more advanced/complex movements (Coordination)
  2. Slow movements to faster movements (speed)
  3. Low force to higher force (Strength/Power)
  4. Short Duration to longer duration (endurance/stamina)
  5. Over greater distance or range of motion (flexibility)
  6. Increased Specificity or decreasing the margins of acceptable movement (Accuracy)
  7. Changes in direction (running backwards, laterally) (Agility)
  8. Increased function decentralized from base of support or center of gravity – example Squats (bilateral movement) vs Pistols  (unilateral movement) (Balance/stability)

Our ability to progress is not limited to solely adding more weight or running faster.  The challenge of being a good coach is understanding the importance of how to use the range of stressors to improve adapation. Similarly, understanding how much stress and when can determine the success of our athletes. If the stress is too little or too infrequent our bodies will never feel the need to get better. If we apply too much stress or stress too frequently then we risk over training and injury,


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