When Athletes Stop Adapting: Recognizing Low Energy Availability Before It Becomes RED-S

Every strength and conditioning coach has worked with an athlete who appears to be doing everything right. They never miss training sessions, consistently push themselves in the weight room, and demonstrate an unwavering commitment to improving their performance. Yet despite increasing training volume and maintaining excellent discipline, their progress stalls. Recovery slows, fatigue becomes persistent, minor injuries become recurring setbacks, and illnesses seem to occur more frequently. The instinct is often to modify the training program—adding more volume, increasing intensity, or changing the stimulus. However, before altering an otherwise well-designed program, coaches should ask one important question:

Athletic training serves as a deliberate physiological stressor. Whether the goal is increased strength, power, endurance, or hypertrophy, exercise intentionally disrupts homeostasis. The targeted adaptations occur only when the athlete optimizes the Performance Adaptation Triangle.

This framework requires a balanced interaction between an appropriate training stimulus, sufficient recovery, and adequate energy availability. When one side of this triangle is compromised, physical adaptation slows or stops entirely. Chronic low energy availability is one of the most common, yet overlooked, reasons athletes fail to realize the full benefits of their training.

This concept lies at the heart of Low Energy Availability (LEA), the underlying cause of Relative Energy Deficiency in Sport (RED-S). Energy availability refers to the dietary energy remaining for normal physiological function after accounting for the energy cost of exercise. When energy intake consistently fails to meet the combined demands of training and essential biological processes, the body responds by prioritizing survival over performance (Loucks et al., 2011).

Rather than investing energy into adaptation, the body begins to reduce energy expenditure wherever possible. Hormone production becomes suppressed, resting metabolic rate decreases, protein synthesis slows, immune function becomes compromised, bone remodeling is impaired, and reproductive function may be downregulated. These physiological changes represent highly sophisticated survival mechanisms, not training adaptations. Although these responses conserve energy in the short term, they significantly impair the athlete's ability to recover, adapt, and perform (Mountjoy et al., 2023).

Historically, energy deficiency in athletes was described as the Female Athlete Triad, consisting of low energy availability, menstrual dysfunction, and reduced bone mineral density (De Souza et al., 2014). While this framework dramatically improved awareness among clinicians and coaches, subsequent research demonstrated that the consequences extend far beyond reproductive and skeletal health. Recognizing these broader effects, the International Olympic Committee introduced the concept of Relative Energy Deficiency in Sport (RED-S), acknowledging that chronic low energy availability affects multiple physiological systems, including endocrine, metabolic, cardiovascular, gastrointestinal, hematological, immune, and psychological function, while simultaneously impairing athletic performance (Mountjoy et al., 2018; Mountjoy et al., 2023).

Importantly, RED-S is not limited to elite endurance athletes or individuals with diagnosed eating disorders. It can affect athletes of any sex, sport, competitive level, or body composition. Many athletes develop LEA unintentionally by increasing training volume without a corresponding increase in caloric intake, attempting to improve body composition during periods of heavy training, or underestimating the energy required to support recovery. Consequently, athletes may appear healthy, maintain a stable body weight, and continue training at a high level while significant physiological disruption is occurring beneath the surface.

For strength and conditioning professionals, this represents an important shift in perspective. Training is only one half of the adaptation equation. The other half is energy availability. When athletes are inadequately fueled, the body no longer directs resources toward improvement—it simply works to survive. Recognizing when this transition occurs may be one of the most valuable skills a coach can develop.

One concept to discuss with athletes and students is an LEA-specific version of the Performance Adaptation Triangle. Coaches often focus heavily on programming because training is the most visible component of performance. However, adaptation occurs only when three equally important factors are present: an appropriate training stimulus, sufficient recovery, and adequate energy availability.

Training provides the stimulus for change, recovery provides the opportunity to rebuild, and energy availability supplies the biological resources required for that rebuilding to occur. Remove any one side of the triangle and the entire system becomes unstable.

This framework also explains why increasing training volume is not always the solution when performance plateaus. If an athlete is sleeping poorly, recovery becomes the limiting factor. If they are chronically under-fueled, energy availability becomes the limiting factor. Adding more training in either situation simply increases physiological stress without improving adaptation.

For coaches, this shift in thinking is powerful. Rather than asking, "How can I make this athlete train harder?" we should first ask, "What is preventing this athlete from adapting?"

Perhaps the greatest challenge with RED-S is that it rarely presents the way most coaches expect.

Many still associate low energy availability with visibly underweight athletes, eating disorders, or sports that emphasize leanness such as gymnastics, ballet, or distance running. While these athletes remain at increased risk, research now demonstrates that RED-S can occur across virtually every sport and at every competitive level. Strength athletes, team sport athletes, recreational exercisers, and masters’ athletes can all develop low energy availability when training demands consistently exceed energy intake (Mountjoy et al., 2023)

More importantly, athletes experiencing LEA often look healthy. Many maintain a stable body weight, possess well-developed muscle mass, and appear disciplined in their nutritional habits. Others are intentionally trying to improve body composition while simultaneously increasing training volume. In these situations, athletes may unknowingly create an energy deficit large enough to impair recovery despite consuming what appears to be a healthy diet.

This is why RED-S has become what can be referred to as the silent adaptation killer. Athletes continue to train, coaches continue to program, yet the physiological machinery responsible for adaptation is gradually being downregulated. Progress slows not because the training program is ineffective, but because the body no longer has sufficient energy to support the adaptations that training is designed to produce.

From a coaching perspective, this is a critical distinction. The athlete is still working hard. They simply lack the physiological resources to benefit from that work.

One of the earliest observable indicators of low energy availability may not be a laboratory value or formal diagnosis, but a change in how the athlete responds to training. Athletes who previously recovered well may begin requiring longer between sessions, struggle to achieve progressive overload, or experience plateaus in strength, power, and sport-specific performance.

Workouts that were once manageable may also feel disproportionately difficult and be accompanied by greater fatigue, poorer concentration, and reduced overall well-being. A recent systematic review and meta-analysis found that low energy availability was associated with impaired training response and reductions in endurance performance, explosive power, agility, concentration, and sport-specific performance (Gallant et al., 2025). Experimental and longitudinal studies have similarly demonstrated declines in explosive power and competitive performance during periods of inadequate energy availability, in some cases before more obvious hormonal or clinical abnormalities were detected (Jurov et al., 2022; Vanheest et al., 2014). These subtle performance changes may therefore provide coaches with an important early opportunity to ask questions, review training and recovery patterns, and initiate an appropriate referral.

As LEA persists, the consequences become increasingly widespread. Reduced muscle protein synthesis limits recovery and hypertrophy, while suppressed endocrine function contributes to fatigue, impaired adaptation, and, in female athletes, menstrual dysfunction. Bone remodeling slows, increasing the risk of stress fractures and overuse injuries, while immune suppression may contribute to recurrent illness and missed training days (De Souza et al., 2014; Mountjoy et al., 2018).

Psychological changes should not be overlooked. Athletes experiencing LEA may demonstrate irritability, reduced motivation, difficulty concentrating, or increased anxiety. Unfortunately, these symptoms are often attributed to the pressures of competition rather than recognized as potential consequences of inadequate energy availability.

Taken together, these changes create a vicious cycle. Performance declines, prompting athletes to train harder or further restrict caloric intake to regain their competitive edge. Rather than solving the problem, these strategies deepen the energy deficit and further reduce the body's capacity to adapt.

Strength and conditioning professionals are not responsible for diagnosing RED-S, nor should they attempt to prescribe individualized nutritional interventions. Their greatest contribution lies in recognizing patterns, initiating supportive conversations, and facilitating appropriate referrals.

Because coaches observe athletes consistently over weeks, months, and often years, they are uniquely positioned to detect gradual changes that may escape notice during periodic medical evaluations. Monitoring training logs, recovery, performance trends, illness frequency, injury patterns, and, when appropriate, menstrual health can provide valuable insight into an athlete's overall physiological readiness.

Simple, open-ended questions often reveal far more than assumptions:

• How are you recovering between training sessions?
• Have your eating habits changed since increasing your training?
• Are you intentionally trying to lose weight?
• Have you noticed changes in your energy levels?
• Have you experienced recurrent injuries or frequent illnesses?
• For female athletes, has your menstrual cycle changed?

These conversations should always occur privately, respectfully, and without judgment. The objective is not to investigate body weight or appearance, but to understand whether the athlete has the resources necessary to support adaptation.

Perhaps the most important responsibility of the coach is to recognize the limits of their professional scope. When RED-S is suspected, referral to the appropriate interdisciplinary team, including a physician, sports dietitian, psychologist, or other qualified healthcare professional, provides the athlete with the comprehensive assessment and management required for safe return to optimal performance

The most effective strategy for managing RED-S is preventing it from developing in the first place. While nutrition interventions should be delivered by qualified sports dietitians, coaches have tremendous influence over the training environment and the culture surrounding performance.

This is where the Performance Adaptation Triangle provides a practical coaching framework. Every training decision should consider three equally important questions:

1. Is the training stimulus appropriate?
2. Is recovery sufficient?
3. Is the athlete adequately fueled to adapt?

When one side of the triangle is neglected, the entire system becomes unstable. Increasing training volume cannot compensate for inadequate sleep, nor can superior programming overcome chronic low energy availability. Coaches who understand this relationship are better equipped to recognize when the solution to poor performance lies outside the training program.

Creating a performance-focused culture rather than an appearance-focused culture is equally important. Conversations should emphasize strength, recovery, resilience, and long-term athletic development rather than body weight or body composition alone. Athletes should understand that nutrition is not simply fuel for today's workout, it provides the biological resources required to recover, repair damaged tissue, synthesize new muscle proteins, maintain hormonal function, and prepare for tomorrow's training session.

Coaches should also normalize conversations surrounding recovery. Fatigue, recurrent illness, persistent soreness, disrupted sleep, menstrual irregularities, and declining motivation should never be dismissed as signs of insufficient mental toughness. Instead, they should be viewed as valuable physiological feedback indicating that the athlete may no longer possess the resources necessary to support continued adaptation.

Perhaps the greatest shift for many coaches is recognizing that more training is not always the answer. When athletes stop progressing, the instinct is often to increase workload. The more effective question may be, "What is preventing this athlete from adapting?" Sometimes the answer is programming. Often, however, it is recovery or energy availability.

Strength and conditioning coaches spend more time observing athletes than almost any other member of the performance team. This places them in a unique position to recognize the early warning signs of low energy availability long before serious health consequences develop.

RED-S should not be viewed solely as a nutritional concern or a medical diagnosis. From a coaching perspective, it is fundamentally a problem of impaired adaptation. When energy availability becomes chronically insufficient, the body shifts from maximizing performance to conserving energy for survival. The athlete may continue training with remarkable discipline and commitment, but the physiological systems responsible for adaptation gradually begin to shut down.

This is why RED-S can be considered the silent adaptation killer. It rarely prevents athletes from training. Instead, it prevents them from benefiting from their training.

As coaches, our responsibility is not to diagnose RED-S but to recognize when something appears wrong, initiate supportive conversations, and collaborate with qualified healthcare professionals when appropriate. Early recognition can reduce injury risk, protect long-term health, and ultimately preserve athletic performance.

The most successful athletes are not necessarily those who train the hardest, they are those who consistently adapt to training. As coaches, our responsibility extends beyond designing effective programs. We must create environments where athletes have the physiological capacity to benefit from those programs.

Athletes do not adapt simply because they train. They adapt because they train, recover, and fuel appropriately. Remove any side of the Performance Adaptation Triangle, and adaptation becomes impossible.

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