Are You Running on Empty? What Runners Need to Know About RED-S (Relative Energy Deficiency in Sport)
If you’re a dedicated runner, chances are you’ve pushed through a little fatigue now and then. Maybe you’ve even brushed off nagging soreness, irregular cycles, or a string of minor injuries. But what if those are signals that your body is actually under-fueled?
Welcome to the world of Relative Energy Deficiency in Sport (RED-S)—a condition that can impact performance, recovery, and long-term health without any obvious warning signs.
Let’s unpack what RED-S really is, how to spot it early, and what you can do to prevent it.
What is RED-S?
Relative Energy Deficiency in Sport (RED-S) is a condition that happens when your energy intake (aka food) doesn't match the energy you expend through training, recovery, and daily life.
This energy imbalance affects much more than just your running pace—it hits nearly every system in your body:
Hormonal health (like estrogen or testosterone)
Bone strength
Recovery and adaptation to training
Immune function
Cardiovascular performance
Mental sharpness and mood
Severe Signs of RED-S: When the Body Starts to Shut Down
Sometimes the body gives us loud warning signs that something’s off. These include:
🔴 Primary Amenorrhea: No menstruation by age 15 or 5+ years after breast development.
🔵 Secondary Amenorrhea: 12+ consecutive missed periods (due to Functional Hypothalamic Amenorrhea).
🟢 Low Testosterone: Clinically low free or total testosterone (normal range: 300–1000 ng/dL).
Who’s at Risk for RED-S?
You don’t have to be an elite athlete to be at risk. In fact, many everyday runners—especially those chasing weight loss or trying to eat “clean”—unknowingly slide into energy deficiency.
📊 Here’s a visual risk matrix:
Common high-risk profiles include:
BMI < 17.5 or rapid weight loss
Menarche (first period) after age 16
Less than 6 menstrual cycles in a year
Dietary restriction or history of eating disorders
Stress fractures, especially in trabecular bone (hip, spine, pelvis)
But It's Not Just About Periods or Weight
For male and female runners alike, RED-S shows up in performance metrics too.
Here’s what else might be off if you're under-fueled:
Look for signs like:
Plateauing even when training hard
Poor motivation or mental fatigue
Weak strength and endurance gains
Poor recovery after hard workouts
Decline in VO2 max, power, or jump height
These signs are objective and worth tracking, especially if you're aiming to improve performance or recover from injury.
How to Come Back From RED-S: A Return-to-Running Framework
Recovery from RED-S isn't just about eating more. It’s about building back wisely—across physical, hormonal, and psychological dimensions.
Here’s a breakdown of return-to-sport phases:
Phases of Return:
Chill: Rest + medical support
WB’ing & ADLs: Gentle reloading with daily activities
Bodyweight Drills: Pain-free movement basics
Progressive Loading: Add load carefully
Power/Plyos: Reintroduce speed & spring
Return to Participation: Walk-run progressions
Return to Sport (R2S): Full integration, smart intensity
What’s the Difference Between Participation, Sport & Competition?
Just because you’re running again doesn’t mean you’re all the way back.
Return to Participation: You're active, but not yet at full performance.
Return to Sport: You’re training again but not at your pre-injury or pre-RED-S level.
Return to Competition: You’re back at or above your best.
Recovery from RED-S takes time. But done right, it leads to long-term performance gains and injury resilience.
How to Prevent RED-S in the First Place
Here’s the good news: RED-S is completely preventable—if you know what to look for.
Simple strategies that go a long way:
Eat enough. Especially carbs. Especially around training.
Monitor your cycle (females) or libido (males).
Don’t train through chronic fatigue, stress fractures, or burnout.
Work with a running coach, PT, and registered dietitian or nutrition coach who understands endurance performance.
👉 If you're not sure where to start or you feel stuck, schedule a call with a Resolve Physical Therapist! You don’t have to navigate this alone.
Final Thoughts
Fueling well isn’t just about looking lean—it’s about being strong, healthy, and capable. If you’re struggling with unexplained fatigue, performance stalls, or menstrual irregularities, RED-S could be the missing piece.
Listen to your body. Fuel like an athlete. Train with intention.
References:
Mountjoy M, et al. British Journal of Sports Medicine (2014, 2018)
Nattiv A, et al. Female Athlete Triad Coalition (2007)
De Souza MJ, et al. BJSM (2014)
Ackerman KE, et al. Current Sports Med Rep (2020)
Elliott-Sale KJ, et al. Eur J Sport Sci (2018)
