Why You're Getting Slower (And It Might Not Be Aging)

If you're training consistently but your recovery is getting worse, your pace is falling, and every workout feels harder than it used to — it may not be your age. It may be that your body simply doesn't have enough energy to support what you're asking of it.

Here's a pattern that comes up regularly in clinical practice, and I think a lot of endurance athletes are going to recognize it immediately.

A masters male triathlete in his early 50s. Consistent training, declining performance, fatigue that doesn't fully resolve between sessions. He's actually increased his training load over the past year trying to push through the decline. He eats carefully, keeps his weight managed, and by all external appearances is doing everything right. His bloodwork came back normal. He was told he might be overtraining, or just feeling the effects of getting older.

Here's what I found when I dug deeper.

His body didn't have enough energy to support what he was asking of it. Not because he wasn't eating — he was eating. Often quite carefully. But the gap between what he was taking in and what his training actually cost — once you account for everything the body needs to do beyond the workout itself — was large enough that his body had started rationing. Recovery got less. Adaptation got less. Performance declined as a direct consequence.

That condition has a name most athletes have never heard: RED-S. Relative Energy Deficiency in Sport.

Prefer to watch? The full video is below — or keep reading for the expanded breakdown.

What RED-S Actually Is

RED-S stands for Relative Energy Deficiency in Sport. The word relative is the key — because this isn't about eating nothing, and it isn't about clinical starvation. It's about a gap. A gap between how much energy you're taking in and how much your body actually needs to support everything it's being asked to do.

The foundational concept is Low Energy Availability (LEA). Energy availability is the energy you consume from food minus the energy you expend during exercise, expressed relative to lean body mass. What's left over after accounting for exercise is what your body has available to run everything else — organ function, hormone production, immune regulation, bone maintenance, tissue repair, cognitive function, and recovery from training.

When that remainder is chronically too low, your body makes triage decisions. The systems that keep you alive right now get the energy. The systems that support long-term function — recovery, hormonal balance, bone remodeling, adaptation to training — get rationed or shut down.

That's RED-S. Not starvation. A chronic mismatch between energy in and energy needed, with consequences that ripple across almost every physiological system in the body.

RED-S replaced an older term — the Female Athlete Triad — which described low energy availability, menstrual disruption, and bone density loss specifically in women. RED-S is the broader, updated framework that recognizes this condition affects male athletes as well, and that the consequences extend far beyond those three original markers.

Who Actually Gets RED-S

The stereotype is a lean, competitive, younger female endurance athlete. That profile is real. But in clinical practice the range is significantly broader — and that narrow stereotype is one of the primary reasons so many athletes go undiagnosed.

Masters athletes over 40 are at genuinely higher risk than most people realize. Metabolism shifts with age. Many masters athletes are more conscious about body composition than they were in their 30s. The combination of disciplined eating, high training volume, and a metabolism operating differently than it used to creates exactly the conditions where LEA develops — often without any intention of underfueling. The triathlete described above is not an outlier. He's a representative case.

Male athletes develop RED-S. The physiology is the same regardless of sex. The consequences are equivalent. What male athletes don't have is the most visible marker — menstrual disruption — that often triggers investigation in women. So male athletes get dismissed even more readily, because the conversation about this condition has historically been framed as a women's issue.

Athletes eating genuinely healthy diets can have RED-S. This is the point that surprises people most. Clean eating, whole foods, avoiding processed food — none of that determines energy availability. The quantity of food relative to training load does. An athlete eating nutritiously but insufficiently for what they're asking their body to do can develop every consequence of this condition. Healthy eating and sufficient eating are not the same thing, and treating them as equivalent is one of the most common reasons RED-S goes unrecognized.

What RED-S Actually Feels Like

The symptom picture is broad — which is part of why individual symptoms are easy to explain away as training fatigue, stress, or aging. It's the pattern of multiple symptoms occurring simultaneously that matters.

Fatigue that doesn't resolve with rest is the most consistent symptom. Not post-training fatigue, which is expected. A baseline tiredness that doesn't lift with recovery days or adequate sleep, and makes training feel harder than it should for a given effort level. Athletes describe it as always starting sessions already behind.

Performance decline that doesn't track with training is usually what drives athletes to start looking for answers. Times getting slower. Power dropping. Perceived effort increasing for the same objective output. Something is limiting the adaptive response. That something is frequently inadequate energy availability — the body doesn't have the substrate to convert the training stimulus into adaptation.

Slow or incomplete recovery — soreness that used to clear in 24 hours now lingers for three or four days. Minor soft tissue issues that used to resolve quickly become recurring complaints that never quite go away.

Recurrent illness, particularly upper respiratory infections, signals immune compromise. The immune system is metabolically expensive to run, and it's one of the first systems deprioritized when energy is chronically insufficient. Athletes who are getting sick more frequently than their training would seem to explain are often experiencing exactly this.

Stress fractures disproportionate to training load are among the most medically serious consequences — and frequently the finding that finally prompts the right investigation. When energy availability is chronically low, bone formation is reduced while resorption continues. Bone density quietly declines. A stress fracture in an athlete who hasn't dramatically increased training load should raise immediate suspicion about energy availability.

In women, menstrual disruption is an important signal when present — irregular or absent cycles indicate the reproductive hormone system has been deprioritized under energy scarcity. But its absence does not rule RED-S out. Some women maintain apparently regular cycles even with significant LEA. Perimenopausal women may miss this signal entirely because cycle changes seem explained by age. And male athletes don't have this marker at all — which is why it cannot be the primary diagnostic criterion.

Mood and cognitive changes — irritability, low motivation, increased anxiety, difficulty concentrating, mental fog, reduced decision-making during training and racing — round out the picture. In isolation these are easy to attribute to life stress. In the context of the other symptoms above, they're meaningful data points in a recognizable pattern.

Why This Gets Missed So Consistently

Understanding why RED-S goes undiagnosed as often as it does requires looking at both the athlete side and the clinical side.

From the athlete's perspective, most of the symptoms — fatigue, performance decline, slow recovery, mood changes — are also expected consequences of hard training. Athletes conditioned to push through discomfort interpret these as things to train harder against rather than signals to investigate. The characteristics that make someone a committed endurance athlete — high pain tolerance, strong intrinsic motivation, comfort with suffering — are the same characteristics that make them less likely to recognize when something physiologically serious is actually wrong.

There's also a cultural layer that's worth naming directly. Endurance sports carry a largely unexamined narrative that leanness equals performance, and that eating discipline is a virtue. In that context, eating more feels like backing off rather than solving a problem. The athlete who is underfueling often frames it internally as staying disciplined. The framework that's supposed to be serving performance is actively working against it — and the culture makes it hard to see.

From the clinical side, standard bloodwork in early RED-S frequently looks unremarkable. Basic metabolic panels, complete blood counts, thyroid panels — all can appear within normal limits even when LEA is significantly affecting physiology. Without looking for the specific markers that reflect energy availability and its downstream hormonal consequences, and without interpreting results through a performance lens rather than a disease-screening one, the workup comes back normal. And a normal workup ends the investigation.

This is why athletes with RED-S frequently spend months or years being told everything is fine — because everything is fine by the metrics being used. Not by the metrics that would actually answer the question.

Could You Have RED-S Without Realizing It?

Yes. Quite easily. The condition develops gradually. The symptoms overlap substantially with expected training consequences. The cultural context of endurance sport actively discourages recognizing underfueling as a problem. And standard medical workups aren't designed to find it.

The pattern to watch for: consistent training, declining performance, fatigue that doesn't resolve with rest, slow or incomplete recovery, and a diet that's health-conscious but may not be calibrated to your actual training load. If several of those things are simultaneously true — and you've already been told everything is normal — this is worth investigating specifically, with someone who's looking for it and knows what to look for.

The next piece of this series answers the question that naturally follows: why does eating just a little too little affect almost every hormone in your body, even when your diet seems genuinely healthy? That's where the real downstream urgency of this condition becomes clear — and where the connection between energy availability and the hormonal picture we've discussed throughout this series comes fully into focus.

Dr. Jason Barker is a naturopathic doctor with over 20 years of clinical experience working with endurance athletes. He is a two-time Ironman finisher and the founder of Natural Athlete Clinic. For individualized evaluation of energy availability and its downstream consequences, visit naturalathleteclinic.com.