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The Science of Progress: The S.A.I.D. Principle in Fitness for Better, More Consistent Results

Do you ever notice how the more you perform a task the better you get at doing it? The human body is incredibly adaptable. This is known as the S.A.I.D. principle, or specific adaptation to imposed demands. What this simply means is that whatever stimulus regularly happens to your body, your body will adapt to be more efficient at. How can you use this information? To put it simply, do more of what you want to be better at: if you want to be fast then run fast, if you want to be strong then lift heavy, but the level of specificity is what is often overlooked.

Let’s use the example of trying to run a faster 5k (3.2 Miles). Going into the gym and performing barbell back squats, deadlifts, and calf raises will increase your leg strength, and there is some level of carryover from the benefits of these lifts to running, but these lifts neglect the actual task of running and adapt your body's energy systems for strength training instead of the goal of running.

a person running training

So how should you train?

The simple answer would be to run, but that answer remains general and not specific. You would need to assess your previous runs to find out specifically what you need to focus in on. If your 1-mile splits are: 8 minutes, 9 minutes, and 13 minutes, you can see a the effects of fatigue towards the end of your run and it would be wise to focus on endurance running at distances beyond a 5km (3.2 Mile) run, like a 4 or 5 mile run added in until your 1-mile splits are closer together. Let’s say your 1-mile splits are closer now and are 8, 8, and 9 minute miles. The effects of fatigue are no longer the issue and now the focus should be on speed, so the addition of faster paced runs at shorter distances like adding speed miles to your normal training routine to train your body to run at faster paces. All of this is assuming your running form doesn’t need any changes, and for all of these elements you should look into getting a coach who can assess your running mechanics and provide feedback to everything discussed so far and make suggestions to where supplementary training like the addition of strength training would be most beneficial.

Now our training is specific, but what about our lifestyle?

For most, our training only encompasses about an hour of our day, but the adaptations continue throughout the rest of our day through our jobs, leisure activities, and even how we sleep. More and more jobs are becoming automated in some way causing many workers to shift to more desk jobs. Your body is adapting to this too. A study out of Georgetown University suggests that roughly 65% of American adults live with some form of lower back pain. The leading cause of low back pain comes from what is commonly referred to as lower crossed syndrome. This is caused by the adaptations of glute and abdominal muscles becoming underactive and lengthened and/or overactive and shortened hip flexors and erector spinae muscles, usually due to prolonged sitting and/or sedentary activity (as illustrated below). This creates a forward tilt of the pelvis and places stress on the lower back that can express as low back pain, a bulging disc, or even nerve pain/damage.

lower crossed syndrome

With the growing dependence on cell phones in everyday life there has been an increase in what is known as upper crossed syndrome. Similar to lower crossed syndrome, it leads to similar tightened and overactive upper trap and pectoralis muscles with lengthened and underactive lower trap muscles and neck flexors. The same thing occurs with upper crossed syndrome pulling the head forward and placing stress on the cervical spine that can lead to neck pain, disc bulge, and nerve pain/damage.

upper crossed syndrome

How do you prevent this?

The short answer is to lengthen your tight muscles and strengthen your weak muscles, and you can do some of this in the gym, but it also comes from lifestyle changes like utilizing a standing desk and being aware of your posture when you’re on your cell phone. These examples illustrate the negative effects of the S.A.I.D. principle and can put you at risk for injury.

So how much change can you actually make to your body by being intentional about your training?

Most believe that your genetics play a major role in your muscle fiber types and that you only have the ability to change them by a few percent; however, in 2018 Dr. Andy Galpin published a study on identical twins. One twin regularly competed in high level endurance events for over 30 years while the other lived a relatively normal, sedentary adult lifestyle. The results were staggering, the twin who competed in endurance events has 55% more slow twitch muscle fibers than their sibling, making them way more efficient at endurance events than their twin. Twin studies are rare and hard to come by, and this is too small of a sample size to come to an absolute conclusion, but it provides evidence that we have way more control over the development of our muscles than previously expected. These changes happened over 30 years and we don’t know how long it would take to make significant changes like in this study, but if it takes that long to change your body, then right now is the best time to get started.

If you’re interested in pursuing a specific fitness goal or lifestyle changes, schedule a consultation with a Fit Societe coach here: or sign up for our upcoming fitness challenge complete with a membership, dexa scan, t-shirt, and great educational opportunities from our amazing coaches here:


Jake Passot, MS, CSCS, CES, USAW-1, FMS-1, XPS, OLP, is a Fit Societe Performance Coach specializing in sports performance and corrective exercise. He attended San Diego State University and earned his bachelor's degree in Kinesiology with an emphasis on fitness specialist as well as his master's degree in Exercise Physiology. He is a disabled veteran who is passionate about encouraging active lifestyles while remaining pain-free and maximizing human performance.


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