Running on Empty: How Low Energy Availability Quietly Breaks Athletes’ Bones

Stress fractures are often blamed on overtraining, poor footwear, or sudden increases in exercise intensity. While these factors certainly play a role, they do not tell the full story. A growing body of sports medicine research shows that many athletes who develop stress fractures are not simply training too hard — they are not fueling their bodies adequately for the demands placed upon them.

This imbalance between energy intake and energy expenditure is known as Relative Energy Deficiency in Sport. It affects bone strength, hormonal balance, immune function, and overall athletic performance. When left unrecognized, it significantly increases the risk of stress fractures and delays healing.

This article explores how Relative Energy Deficiency in Sport develops, why it weakens bones, how it leads to stress fractures, and what athletes, coaches, and healthcare providers need to know to prevent long-term damage.

Relative Energy Deficiency in Sport occurs when an athlete’s dietary energy intake is insufficient to support both basic physiological functions and the demands of training and competition. In simple terms, the body does not have enough energy left over after exercise to maintain healthy systems such as bone remodeling, hormone production, and tissue repair.

This condition was formally recognized by the International Olympic Committee as an expansion of the earlier concept known as the Female Athlete Triad. Importantly, Relative Energy Deficiency in Sport affects both males and females, across all ages and sport types, including endurance sports, aesthetic sports, and weight-class sports.

Bone is a living tissue that constantly remodels itself. New bone formation requires adequate energy, protein, calcium, vitamin D, and hormonal support. When energy availability is chronically low, the body shifts into conservation mode, prioritizing essential survival processes over bone maintenance.

Low energy availability disrupts:

• Bone formation rates
• Calcium absorption
• Vitamin D metabolism
• Hormones critical for bone strength, such as estrogen and testosterone

As a result, bones become more fragile and less able to withstand repetitive mechanical stress.

Stress fractures develop when repetitive loading exceeds the bone’s ability to repair itself. In athletes with Relative Energy Deficiency in Sport, this threshold is reached much earlier.

Key mechanisms include:

• Reduced bone mineral density
• Impaired microdamage repair
• Increased bone resorption
• Suppressed reproductive and metabolic hormones

Studies show that athletes with low energy availability have significantly higher rates of bone stress injuries, even when training volume appears appropriate.

Relative Energy Deficiency in Sport can occur in any sport, but it is especially prevalent in:

• Distance running and marathon training
• Gymnastics and figure skating
• Ballet and dance
• Cycling and triathlon
• Rowing
• Combat sports and weight-class sports

In these disciplines, athletes often face pressure to maintain a lean physique, which can lead to chronic underfueling and increased fracture risk. (American College of Sports Medicine)  

Relative Energy Deficiency in Sport often develops gradually, making early detection challenging. Warning signs may include:

• Recurrent stress fractures or slow bone healing
• Persistent fatigue despite adequate rest
• Decline in performance or endurance
• Frequent illnesses or infections
• Muscle weakness or loss of coordination

Additional red flags include:

• Irregular or absent menstrual cycles in females
• Reduced libido or low testosterone symptoms in males
• Cold intolerance
• Gastrointestinal disturbances
• Sleep disturbances

While mechanical stress is necessary for stress fractures to occur, it does not explain why some athletes fracture bones while others tolerate similar training loads. Relative Energy Deficiency in Sport provides the missing biological explanation.

Athletes with adequate energy availability can adapt to training stress by strengthening bone. Those with energy deficiency cannot, making injury almost inevitable over time (Mayo Clinic).

Diagnosing Relative Energy Deficiency in Sport requires a comprehensive approach that includes:

• Detailed dietary history
• Training volume and intensity assessment
• Injury history, especially recurrent stress fractures
• Menstrual or hormonal history

Stress fractures are commonly diagnosed using magnetic resonance imaging or bone scans. However, identifying the underlying energy deficiency may require:

• Bone mineral density assessment (DEXA scan)
• Hormonal evaluation
• Nutritional analysis

The American Academy of Orthopaedic Surgeons emphasizes that treating the fracture alone without addressing energy deficiency leads to high recurrence rates.

Relative rest from impact activity is required to allow stress fractures to heal. However, rest alone does not correct the underlying metabolic problem.

The foundation of treatment is restoring adequate energy availability through:

• Increased total caloric intake
• Balanced macronutrient distribution
• Adequate calcium and vitamin D intake
• Timing nutrition around training sessions

Working with a sports dietitian is strongly recommended (International Olympic Committee).

As energy availability improves, hormonal function gradually normalizes. This process is essential for restoring bone strength and preventing future fractures. Hormonal recovery often takes weeks to months and requires consistency.

In many cases, low energy availability is not accidental. Pressure to maintain body weight, fear of performance decline, or distorted body image can contribute to chronic underfueling.

Addressing psychological factors is crucial for long-term recovery. Sports psychologists and mental health professionals play an important role in preventing relapse (American Psychiatric Association).

Returning to sport before energy balance is restored significantly increases the risk of recurrent stress fractures. A safe return requires:

• Pain-free daily activities
• Evidence of bone healing on imaging
• Normalization of energy intake
• Restoration of hormonal markers

Gradual reintroduction of training volume and intensity is essential (British Journal of Sports Medicine).

Failure to recognize and treat Relative Energy Deficiency in Sport can lead to:

• Chronic low bone density
• Recurrent fractures
• Early osteoporosis
• Fertility issues
• Cardiovascular complications
• Persistent performance decline

Research shows that bone loss during adolescence and early adulthood may never be fully recovered, increasing lifelong fracture risk (National Institutes of Health).

Key prevention strategies

Preventing Relative Energy Deficiency in Sport and stress fractures involves:

• Educating athletes about fueling needs
• Avoiding early sport specialization
• Monitoring training load increases
• Encouraging open communication about fatigue and pain
• Normalizing rest and recovery

Coaches and parents play a critical role in creating environments where health is prioritized alongside performance.

Athletes should seek evaluation if they experience:

• Recurrent or unexplained stress fractures
• Persistent bone pain with activity
• Menstrual irregularities or hormonal symptoms
• Unintentional weight loss with increased training

Early intervention dramatically improves outcomes and reduces long-term damage.

Relative Energy Deficiency in Sport is not a niche diagnosis or a problem limited to elite athletes. It is a widespread, underrecognized condition that directly contributes to stress fractures and long-term bone health consequences.

Strong bones are built not only through training but through adequate energy, proper nutrition, and hormonal balance. Addressing low energy availability early protects athletic careers, long-term health, and overall well-being.

References: