Blood Testing for Athletes: Improving Performance and Outsmarting the Competition
Should athletes turn to blood tests to improve their performance?
Updated December 6, 2023.
Blood analysis provides a unique window into an athlete’s health and performance. Certain biomarkers like vitamin D and ferritin can directly impact athletic performance, while others like cortisol and creatine kinase can provide insights into overtraining and injury prevention. Athletes can now rely on blood testing to pinpoint focus areas and implement effective changes to improve performance.
Here's how athletes, including Olympians, CrossFitters, ultramarathoners, and others, use InsideTracker blood testing to optimize their health and performance.
Sarah Hammer used blood testing in preparation for the Olympics
In preparation for the Olympics, US Olympic track cyclist Sarah Hammer spent hours training and building her endurance. But to reach the next level in her performance, she needed to look where she hadn't before—inside her own body. An InsideTracker blood analysis revealed that she was very low in vitamin D.
Blood test for endurance athletes
Vitamin D deficiency is one of the most common nutrient deficiencies across the globe, including among athletes. A 2016 study found that 32% of professional basketball players were deficient in vitamin D, while 47% had low levels of the nutrient. 
Vitamin D plays many essential roles in the body, especially regarding athletic performance. For starters, the vitamin increases muscle mass and strength, improves bone health (along with calcium), increases the size and number of the muscle fibers used for short bursts of speed and power, and improves lower body strength. [2, 3] Furthermore, adequate Vitamin D can reduce inflammation in the body, specifically the inflammatory marker CRP. A meta-analysis from the journal Nutrients found that vitamin D supplementation can lower serum CRP levels by 20%.  What’s more, according to a randomized control trial, low vitamin D levels can also lead to decreased testosterone, especially in men.  Testosterone is an anabolic hormone produced in both men and women that helps increase bone strength and stimulates muscle mass and strength.
Through blood testing with InsideTracker, Olympian Sara Hammer and her coach were provided blood-based insights about her vitamin D status and provided her with a set of evidence-based interventions to effectively increase it. Sarah went on to win two Olympic silver medals in track cycling.
Crystal Seaver uses routine blood tests to overcome fatigue
Ultramarathoner Crystal Seaver crushes 50 and 100-mile races in her spare time. But after a 100-mile race, Seager struggled to bounce back both physically and mentally. Instead of guessing, she analyzed her bloodwork with InsideTracker to learn more about her body before beginning another training cycle. Testing with InsideTracker showed Crystal that she needed to address her iron and ferritin levels.
Once you see it on paper, it becomes real. It also means you know what kind of changes to make to get back to feeling like yourself again. For me, that meant changes to diet, more rest and less exercise, and letting my body fully recover. - Crystal Seaver
Iron deficiency is one of the most common nutritional deficiencies across the globe, especially in women. Athletes, in particular, face a greater risk of low or deficient iron status, as iron is lost during heavy training periods through sweating, running, and gastrointestinal bleeding that can sometimes follow intense workouts.
How does low iron affect athletic performance?
Iron is part of the protein hemoglobin—a component in all red blood cells (RBCs). RBCs are responsible for transporting oxygen to cells, tissues, and organs throughout the body. Iron deficiency, therefore, tends to lead to lower levels of both red blood cells and hemoglobin.  As a result, blood carries less oxygen to muscles and the brain, which can negatively impact performance. [ 8]
Symptoms of iron deficiency can also include:
- Frequent injury
- Weakened immune system
- Chronic fatigue
- High exercise heart rate
Ferritin, a protein that stores iron, is the best indicator of iron in the body, yet physicians do not routinely check this marker. Athletes, especially female athletes, should track ferritin status to avoid fatigue and plateauing during athletic events. InsideTracker provides ferritin, serum iron, hemoglobin, and RBC tests, as well as specific recommendations on how to improve them.
Kris Brown and Raphael "Rufio" Durand use blood testing to prevent overtraining
Kris Brown, endurance athlete, and ultramarathoner, uses InsideTracker to prevent overtraining. After testing with InsideTracker, the athlete discovered he had early signs of overtraining syndrome, including elevated cortisol.
Cortisol, also known as the stress hormone, is a steroid hormone produced by the adrenal glands. It responds to both physical and emotional stress and plays a crucial role in many essential physiological functions. Overtraining may lead to physical stress and high cortisol levels.
If athletes experience a constantly high cortisol state, they face a greater risk of chronic fatigue, high blood glucose levels, and weight gain. In response to his blood test results, Kris implemented the science-driven recommendations provided by InsideTracker, including taking Ashwagandha root daily and whey protein at night.
My test results from InsideTracker had the direct effect of improving my performance by helping me identify and address the specific needs of my body. Still, they also gave me the confidence boost of knowing that, aside from those minor, fixable issues, I was ready to train hard for the biggest race of my life. - Kris Brown
CrossFitter Raphael "Rufio" Durand also uses blood testing to gauge his intensity and determine when to take a break and recover efficiently. Rufio found that when certain biomarkers, such as cortisol and creatine kinase, are elevated, he cannot recover properly.
Creatine kinase (CK) is an enzyme that rises when muscle damage occurs. Test results of this biomarker allow athletes to see how their bodies react to training load and intensity. CK peaks about two to four days after intense exercise and returns to normal levels (< 200 units) over the course of a few days, depending on the intensity of the exercise.
Blood test for marathon runners
This study showed that the CK levels of marathon runners are elevated after endurance training and competition and took about 7-14 days post-marathon to return to baseline. 
There is also a correlation between CK level and injury. A chronically elevated CK will most likely result in muscle pain, weakness, injury, and more—not ideal for top athletic performance.
InsideTracker considers age, gender, ethnicity, and type of athletic activity (swimmers should have a lower level of CK than soccer players, for example), and determines your personalized range of CK. If you are too high, InsideTracker will provide several personalized options for reducing your levels, including dietary changes, exercises, and supplements.
For me, there’s nothing harder than being told to rest, but InsideTracker helps me understand why it’s valuable. - Raphael "Rufio" Durand
Why should athletes use InsideTracker for blood testing?
All sports have had to grapple with athletes seeking unfair advantages at some point in their histories. But blood testing for athletes is a largely untapped medium for achieving that edge in a fair and clean way.
“Athletes are willing to inject their bodies with drugs to get an advantage, so why not withdraw information to improve performance naturally?” says the founder of InsideTracker, Gil Blander. Blander emphasizes that to optimize your body’s physical capabilities, it’s necessary to have scientific evidence about your unique blood biochemistry.
48 blood and dozens of genetic biomarkers
Ultimate Plan: $699/test
HIPAA and SOC-2 protection
InsideTracker is a personalized health and wellness platform that aims to help people optimize their biomarkers to live healthier and longer lives. It analyzes genetics, behaviors, and goals to give you personalized nutrition, fitness, sleep, stress, and supplementation recommendations.
Why choose InsideTracker
InsideTracker offers DNA testing for dozens of genetic fitness, nutrition, and longevity genetic markers. Since genetics influence many aspects of your health, the app can provide helpful context and an action plan. It also integrates with wearable devices to collect real-time health data, tracking factors like sleep, activity, and heart rate.
Pros and cons
Comprehensive blood biomarker testing
Integration with wearables
Encourages retesting every 3 to 6 months
Personalized optimal zones
Customizable Action Plan
Not a replacement for medical care
DNA testing not available outside of the U.S.
The InsideTracker team spent years analyzing thousands of research papers to find the most critical biomarkers to improve physical performance and identify the nutrition, supplements, lifestyle, and exercise interventions to optimize them. Roughly 3,000 potential biomarkers were narrowed down to more than a dozen of the most essential for injury prevention and athletic performance.
What makes InsideTracker unique is its integration of an “optimal zone” in the blood analysis. This number is specific to each person and considers his or her unique demographic information, including age, gender, ethnicity, and activity level, as well as lifestyle and performance goals.
InsideTracker’s sophisticated algorithm determines the optimal zones for each marker based on the latest peer-reviewed research. For example, the normal generic range for a woman’s ferritin level is between 12-150 ng/dL. But InsideTracker recommends that an active woman in her 20s should have blood levels of ferritin between 40-150 ng/dL for optimum performance. If you're not in this zone, the algorithm recommends effective and simple interventions involving diet, supplements, and training modifications that are specific to your needs.
The InsideTracker team created the algorithm to produce the most accurate recommendations for its users based on cutting-edge scientific research extracted from peer-reviewed scientific literature.
Optimize your physical performance with InsideTracker
From amateur athletes to professionals like Sara Hammer and Rufio Durand, InsideTracker has helped thousands of athletes improve their performance. Combining the latest scientific research with information about your body’s unique biochemistry, InsideTracker can make you a more informed, fit, and better athlete.