When it comes to reaching your fitness goals, what you do outside the gym can be just as important as the time you spend working out. Sleep, nutrition, recovery, and stress all play a role, but so do internal markers that are often overlooked.
Biomarkers like iron, cortisol, vitamin levels, inflammation, and hormones can have a major impact on your energy, strength, endurance, and recovery. If any of these are off, it can hold you back — no matter how consistent your training is.
Here’s a breakdown of the key biomarkers that impact your performance and why they’re worth paying attention to.
Hemoglobin & Ferritin
Hemoglobin and ferritin play a major role in how your body performs and recovers during exercise — especially when it comes to stamina, strength, and oxygen delivery.
Here’s why they’re important:
- Hemoglobin delivers oxygen to your muscles.
Hemoglobin is the protein in red blood cells that carries oxygen from your lungs to your working muscles. Oxygen is essential for endurance, power output, and recovery.
- Low hemoglobin = low performance.
When hemoglobin levels are low, your muscles receive less oxygen, which can lead to fatigue, shortness of breath, dizziness, and reduced stamina during workouts.
- Hemoglobin impacts strength and recovery.
Insufficient oxygen delivery can limit muscle strength, slow recovery, and make consistent training feel harder—even when nutrition and programming are on point.
- Ferritin is your iron reserve.
Ferritin stores iron in your body and helps maintain a steady supply. If your ferritin is low—even if your iron levels are “normal”—your performance can still suffer.
- Low ferritin = poor oxygen delivery.
Without enough ferritin, your body can’t respond well to the demands of exercise, which can hold you back in both endurance and recovery.
If you're feeling unusually tired or winded during workouts, it’s worth checking both your hemoglobin and ferritin levels. Optimizing both is key to powering your performance.
Cortisol & DHEA
Cortisol and DHEA work together to determine how well your body handles training stress, recovers, and adapts over time. Looking at their ratio — not just cortisol alone — gives a clearer picture of resilience versus overload.
Here’s how it works:
- Cortisol fuels short-term performance.
Cortisol is a stress hormone that should rise during exercise and fall afterward. This temporary increase helps mobilize energy by breaking down carbohydrates, fats, and proteins to fuel working muscles.
- DHEA supports repair and adaptation.
DHEA is an anabolic adrenal hormone that promotes tissue repair, muscle maintenance, immune function, and overall recovery—counterbalancing cortisol’s breakdown effects.
- The Cortisol:DHEA ratio shows stress balance.
Cortisol is catabolic (breaks tissue down). DHEA is anabolic (builds and repairs). Their ratio reflects whether your body is adapting to training—or struggling to keep up.
- High ratio = chronic stress load.
A high Cortisol:DHEA ratio is commonly seen with overtraining, poor sleep, under-recovery, or prolonged life stress. It’s associated with muscle breakdown, stalled progress, impaired recovery, and increased burnout risk.
- Low ratio = blunted stress response.
A low ratio may indicate inadequate cortisol output, which can impair energy availability, exercise tolerance, and immune resilience—making workouts feel harder than they should.
Tracking the Cortisol:DHEA ratio helps identify recovery capacity, burnout risk, and immune resilience — allowing training, nutrition, and rest to be adjusted before performance declines. Balanced cortisol and DHEA levels help you train hard and recover well so stress works for you, not against you.
Vitamin B12 & Vitamin D
These two vitamins are foundational for performance and overall vitality.
- Vitamin B12 supports energy production.
It helps convert food into usable energy and plays a role in red blood cell formation, which is critical for oxygen delivery during workouts.
- Low B12 = low energy and poor recovery.
A deficiency can cause fatigue, weakness, and even numbness or tingling, making it harder to train consistently and recover well.
- Vitamin D supports muscle strength and immune function.
It also helps regulate calcium levels, which are crucial for proper muscle contraction.
- Low vitamin D is linked to poor strength and higher injury risk.
It can also contribute to mood issues, which may indirectly affect your motivation and consistency in training.
Together, B12 and D are essential for keeping your energy levels high, your muscles functioning properly, and your recovery on track.
C-Reactive Protein (CRP)
CRP reflects the level of inflammation in your body—and chronic inflammation is no friend to performance.
- CRP should be low.
High CRP levels can indicate that your body is under stress, whether from overtraining, illness, or an underlying issue.
- High CRP = slower recovery and more fatigue.
It may also be linked to joint pain, poor sleep, and difficulty building strength or endurance.
- Managing inflammation helps your body repair and grow.
Anti-inflammatory foods, proper rest, and stress management can help keep CRP in check.
Tracking CRP gives you insight into how well your body is handling your training load, and whether it's time to dial it back or double down on recovery.
Creatine Kinase
Creatine Kinase (CK) is an enzyme your body releases when muscle tissue breaks down — something that naturally happens during exercise. While some elevation after a tough workout is normal, consistently high CK levels can be a red flag.
Here’s why it matters:
- CK rises when your muscles are under stress.
Strength training, endurance workouts, or any intense physical activity can cause temporary spikes in CK as your muscles repair.
- Too much CK = poor recovery or overtraining.
If your levels stay high over time, it may mean your body isn’t recovering well between sessions — or that you’re pushing beyond what it can handle.
- Tracking CK helps you personalize your training.
Monitoring your CK levels can give you insight into when to push harder and when to scale back, helping you avoid burnout and injury.
- Baseline matters.
CK levels vary widely between individuals. What’s more important than the exact number is how it compares to your personal baseline— and how it responds to your training load.
Creatine Kinase can help you tune into your body’s recovery needs, so you can train smarter, stay consistent, and reduce your risk of setbacks.
Testosterone
Testosterone doesn't just have to do with sex drive — it’s a major player in your physical performance.
- It helps build and maintain muscle mass.
Healthy testosterone levels support muscle growth, strength, and power.
- It aids recovery.
Testosterone is involved in protein synthesis, which helps your muscles repair and grow after workouts.
- Low testosterone = lower strength, energy, and drive.
It can also lead to poor recovery, increased fat gain, and decreased motivation.
Whether you're male or female, optimal testosterone levels are essential for maximizing results from your workouts and maintaining muscle as you age.
The Bottom Line
Your workout performance isn’t just about how hard you train, it’s also about what’s happening inside your body. Monitoring and optimizing markers like iron, ferritin, cortisol, vitamins B12 and D, CRP, CK, and testosterone gives you a deeper look into how your body is functioning, where it may be struggling, and what you can do to perform and recover better.
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.