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RED-S Part 1: More Than A Triad

Updated: Mar 23, 2023

In 2014, the IOC expanded on a concept known as the Female Athlete Triad which included Low Energy Availability, Amenorrhea (loss of period for greater than 6 months), and Low Bone Density. The expanded model is called Relative Energy Deficiency in Sport (RED-S). RED-S expands the Female Athlete Triad to acknowledge the effect of low energy availability on multiple physiologic systems, including cardiovascular, gastrointestinal, psychological, immunologic, in addition to endocrine, reproductive, and musculoskeletal systems (1). This also dropped the sex specific qualifications, appropriately acknowledging that men also can suffer from low energy availability that affects their health and performance. I personally like that the new acronym that they chose no longer spells FAT :)

Image from RED-S CAT (2).

Another important component of the RED-S model is that it notes that you can be in a Low Energy Availability state (LEA), but not underweight. This LEA may be intentional as a result of disordered/restrictive eating habits or a clinical eating disorder, or unintentional due to lack of knowledge or resources (i.e. not packing a post workout snack). We often think of energy, in the form of calories, as a simple in versus out equation. However, if there is inadequate energy surrounding training, our bodies will shunt energy away from bodily functions like hormone production, the immune system, and digestion to fuel muscular activity. The graphic below from a blog by Dr. Nicky Keay on the British Journal of Sports Medicine website shows how excessive training or under fueling decreases the energy available for basic life functions.

You can thank evolution for this energy conservation: the body doesn’t know the difference between trying to outrun an opponent versus trying to outrun a bear, and your body wants you to have the energy to survive. Our body has nifty ways to maintain homeostasis, and make sure it has enough energy to outrun bears, so while someone may initially lose weight in a LEA state, their weight may stabilize in a chronic LEA state (3).

Therefore, using low body weight as a screening for LEA or RED-S is not sufficient. There are many other symptoms that raise concern for LEA and RED-S, including but not limited to:

· Decreased performance despite progressive training (4)

· Poor recovery from workouts

· Recurrent injury or a bone stress injury

· Repetitive sickness

· Feeling chronically fatigued (5)

· Decreased heart rate variability

· Digestive difficulties

A combination of awareness of certain markers including an athlete’s fatigue, menstrual cycle and/or libido, heart rate, perceived exertion, intensity and duration of activity, and perceived cognition can help to detect LEA early, before injury occurs. This takes a team effort, with both athletes and coaches (and parents as appropriate for younger athletes), keeping a finger on the pulse of their athlete, figuratively and sometimes literally.

Diagnosis of RED-S is a diagnosis of exclusion, meaning that other causes of symptoms (such as a primary hormone dysfunction, primary GI issue, primary gynecological problem etc.) need to be ruled out first. If an athlete is experiencing symptoms of RED-S, even if they don’t *think* that they’ve been under fueling, they should see a medical doctor to determine if LEA may be the root cause of their symptoms.

In a follow up blog, I will discuss the return from RED-S, and what an athlete’s recovery may look like.

Thanks for reading!

Dr. Elizabeth Karr PT, DPT



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