A Roadmap to Increasing Durability of the Body: Enter Creatine Kinase

By Carl Valle, September 6, 2015


The biomarker creatine kinase (CK) is a useful way to determine general body strain. Anyone who exercises, ranging from light fitness to elite athletes, can benefit from correctly interpreting its data. Unlike vitamin D, ferritin, and magnesium, CK is not a nutrient and thus requires a little extra analysis to take advantage of the information it provides. The average Joe recreational runner all the way to the sports scientist can use CK to improve workouts and unveil some training patterns. In this blog, we will look at CK in detail and offer an outline of how best to use it to gauge body strain so you can plan smarter workouts.

What Creatine Kinase Means to You

When most exercisers or sports professionals hear “creatine kinase,” they think of the supplement creatine phosphate. Some health professionals or nutritionists may think of creatinine, another biomarker that evaluates renal or kidney function. Without getting into unnecessary science beyond basic definitions, creatine kinase is an overall measure of tissue breakdown. CK is valuable because it enables anyone to gauge how their body is responding to training loads: mileage for runners, work done in the weight room, how overall seasonal training is going, and so on. What the biomarker CK is actually indicating is the following:

how much released in the blood stream of what is normally found inside the tissue cells, a sign of muscle damage from overloading the body.

To properly use CK as a marker of training load, you need careful interpretation and good recordkeeping to tease out what is really going on so the information is valid and actionable. From a practical perspective due to the frequency of testing, CK is a wonderful way to calibrate wearable tools and is used in research to help estimate the strain on athletes. CK is also perfect for coaches and athletes to see if mental stress is the reason for high cortisol or poor cortisol- to-free testosterone ratios in training, since in most instances CK only represents muscular breakdown.


CK was used as a cardiac damage biomarker in the past, but now it’s mainly employed as a muscular overload measurement. Nearly everyone involved with exercise is familiar with delayed onset muscle soreness (DOMS), and CK usually peaks in the blood a few days after strenuous training. The science behind why athletes are sore is a little cloudy, but we do know that soreness and CK are correlated in much of current literature.

How to Look at the Numbers Practically

When InsideTracker users look at their data, the first question is, am I in my optimized zone? The optimized zone for CK is what it should be either at rest or after an easy session. Being elevated out of their zone is normal, provided they are training and the rise is due to the natural part of muscle breakdown from typical training.


Users of InsideTracker will sometimes see a score in the red zone and that is often when one has went a little too far on a workout or is not accustomed to new types of training or exercise programs. Smarter training and better timing of blood testing can improve the information on their training or exercise routine.

When training moves from normal extremes and becomes dangerous, the possibility of rhabdomyolysis—the breakdown of muscle fibers and subsequent release of their contents into the blood—arises. Hospitals use CK to help diagnose rhabdomyolysis. Fortunately its likelihood for the average person and even elite athletes training hard is a rare event. One trying to improve performance should be looking to do as much as necessary, not as much as possible. Some dinosaur coaches use training as punishment and at times overly enthusiastic trainees may go too hard, but data-driven InsideTracker users are unlikely candidates for rhabdomyolysis.

Athletes training heavily or neophytes exercising for the first time may see their numbers elevated far out of the zone, creating an unnecessary fear that training is not going well or even that they are overtraining. The CK biomarker can’t be seen as a positive or negative test for overtraining, but rather as a measurement of how your body handled the load over several days before testing.  It can be tricky to see every workout and try to use the number presented to equate to total body damage, but treat CK as another piece of the puzzle to decide where to go.  I base my use of CK on the best practices of far smarter sport scientists. I am looking for clear hints or clues that answer key questions nearly everyone wants to know:

  • Does the CK number represent how hard I am training?
  • Can the CK number explain why I am injured and performing poorly?
  • Should I change or fine-tune my program based on my results?

The answers are maybe, yes, and definitely. CK is a summary-type biomarker of mechanical strain to the muscular system for the most part, so training hard and muscle damage may not be a perfect match. For example, pool recovery workouts that many runners include in their routine may challenge their heart and lungs, but for the most part that training is low-impact for muscles.


Sometimes a race or competition may get athletes into the red zone (high risk) and that is normal an expected. Most of the time yellow is common fro heavy training. Anyone to see if they are fully recovered should be in the green or Optimized zone.

Chronically elevated CK during competition and training can spell injury, and using blood testing to audit rest days and recovery phases is extremely valuable when training is heavy. CK can be combined with other familiar data points, such as GPS and heart rate information. Finally, those doing more power training want to know how fresh they are for workout sessions requiring high rates of speed or explosive strength.

Why Timing of Testing Matters

Some professional teams measure CK weekly or multiple times a week by pricking players’ fingers or something similar. While that is clearly more insightful from the increase of data, it may not be necessary for elites. And it’s not practical for the average person. Three years ago, several professional coaches asked what can one gets from testing once a month or even less. The answer is simple when one uses blood analysis to calibrate recovery instead of measuring muscular breakdown. Nearly every day is a grind, thus the data can be a chore and hard to manage.


Creatine Kinase after a demanding event peaks days later, and a simple way to monitor training and competition is to test 2 days after the hardest session or after an event like a game or race. Recreational athletes and fitness users can test at any time, but they have to be cognizant of how CK rises and falls after strenuous training.

Instead, it’s far smarter to look at the calendar and focus on training milestones and related benchmarks. Like InnerAge for overall health and performance, anyone using CK should focus on unloading periods or light training phases to check that they are truly restored during each stage of the season.  Testing all the time is nice, but the reality is that most users want to see the results of the time they invest. It doesn’t matter when you test, but make sure the timing of the test answers the questions you want to know about.

Testing for Recovery from Heavy Training- After weeks of heavy training, many training programs take a few days to unload a bit, typically 3-7, to restore the body. Testing 72 hours after the last hard session or after the conclusion of the rest period can objectively show the body is rested. One should be in the green or Optimal Zone after prescribed or planned rest.

Testing for Readiness to Perform or Tapering- Coaches and athletes, even recreational ones, can try to come into an event fit (prepared) and fresh (properly rested) to improve their performance.  It’s tempting to try to test before the event to try to make last minute adjustments, but a wiser option is to test the week or days before and see after the competition if the plan worked or not. Seeing results before the competition can backfire if they are not positive, so a little bit of “wait and see” is needed to prevent a negative self-fulfilling prophecy. One should be in or near the optimized zone.

Testing to Push the Limits- Any coach or training program can make someone tired and sore, but the purpose of workouts are to improve the body, and how much and how hard isn't a perfectly clear recipe. During the heaviest part of training it's perfectly fine to see what is going from the inside and later test again when one is rested and expected to do well to see if the plan worked. After competition testing is very helpful to see what the "cost of doing business" was and see if the next attempt can better prepare for the event.

CK is an excellent biomarker but no magic single bullet exists with monitoring and managing nutrition and training, so combining CK with the other markers of the body is the best approach. Looking at Free Testosterone, Cortisol, SHBG, and even hs-CRP are great data points to paint a very wide picture of how the body is responding to mechanical and life stress. 

One can overthink when the best time to test is, but the answer is anytime is good, and the results should match what is expected. When the data doesn't jive, make the right changes from the recommendation and test again to get on the right track.

Appreciating Trends and Merging Your Device Data

Retesting compounds the value of the original blood results, so every user not only screens, they can also see if their strategy to improve is working. The third test is the most telling, since it takes a minimum of three data points to see a trend. When CK is repeatedly high, it means one is not recovering as planned. It may also be a way to see if one is adapting, if the number drops when the training load remains the same or increases. Many athletes and active people take very little time off. By creating a repeatable process of evaluation, no one has to be completely rested to get good insights.


Anyone using monitoring tools like Omegawave, FirstBeat, Polar, Garmin, Suunto, and in this case Myithlete.com can get more objective value by adding blood analysis.

When multiple object data points that traditionally were the sole ways to measure training are used, the synergy is very exciting. Simple data like total mileage or total weight can help recreational runners and fitness enthusiasts stay informed. But professional teams now want to see how the “cost of doing business” truly affects the body. While TrainingPeaks and many software products can store blood data, in the coming months expect more pioneering companies to provide composite metrics that merge sensor data with biomarker scores.

The Roadmap for Durability

The formula for success with most sports or activities is simply to be available to participate meaningfully. Removing the need for exotic equations and complicated math, nearly everyone wants to do more or recover faster. Each year, whether it’s a professional athlete preparing for the rigors of a long season or a 77-year-old female bodybuilder making sure her training in on pace, the process is very similar to farming: Plant the seeds, till the soil, and harvest at the right time.

Unfortunately we are seeing a major decrease in durability, which has much to do with the lack of preparation for the season because of longer competitive periods. It might provide job security for those working with athletes as overtraining and fatigue are a delicate balance. Don’t train so hard that athletes are at risk for having the sport overload them. Train too hard and the workouts can be blamed as the culprit for injury. When teams get the injury bug, usually the strength coach is first to go—not the head coach who may be simply doing too much or not organizing the sessions to match the body responses.


The new exercise tools with InsideTracker can improve the precision of training by adding more profiling variables that adjust the optimal zones for each individual.

The solution to keeping athletes on the field or increasing durability is training smarter, specifically training with more precision. Coaches knowledgeable about the right training “dose” call it the Goldilocks Method, giving just the right amount at the right time for athletes to adapt to. Training with higher degrees of precision with all of the monitoring tools that estimate fatigue and readiness is common now, even with recreational consumers. Proxy measurements like autonomic data and or external loading options from wearable sensors still use blood to validate them, otherwise the companies that want to show credibility wouldn’t use research that incorporates blood analysis. Anyone wanting to get better can do so easily by simply taking a peak under the hood and ensuring that the trend is going as well as planned.


What is your CK telling you?


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