Complications from the Injury Cycle: RED-S

Complications of the Injury Cycle: RED-S

By Cat Fitzgerald PT, DPT, CSCS

As this blog series has been discussing, the injury cycle is defined by recurring or chronic injury, and it could be the same injury or a different one that happens. This can be perpetuated by a race calendar or by only partially addressing a chronic injury.

A serious complication of the injury cycle is RED-S.

This can work either way: RED-S can be a contributing factor to injuries, or it can develop once a runner is in the injury cycle. RED-S, or Relative Energy Deficiency in Sport, is defined as “impaired physiological functioning caused by relative energy deficiency and includes, but is not limited to, impairments of metabolic rate, menstrual function, bone health, immunity, protein synthesis, and cardiovascular health”.1 The direct underlying cause for this is low energy availability, which occurs when a runner’s energy intake (eating) does not match their energy output (exercise). 

RED-S has become more well known over the past few years. Articles have appeared in popular magazines, such as Runner’s World and Women’s Running, and among evidence-based professional groups including the International Olympic Committee and the American Academy of Family Physicians.

Let’s look at an example of how RED-S develops after an injury occurs–the less obvious scenario.

A runner has developed IT band syndrome and is working through the injury in physical therapy. They are continuing to run under the guidance and instruction of the PT, but the weekly mileage is significantly lower and all of the runs are currently easy–no speed work. Often, this runner will begin to restrict their food intake as a result of the decrease in their running volume. This can look very different runner to runner. It might be strategic, such as cutting carbohydrates, with the (incorrect) logic that carbs aren’t needed due to the decrease in running. Or it might look like eating less overall–which can happen naturally with running less–but here we’re talking about restricting to the point where the runner does not have enough energy intake to match the output. It’s important to recognize that this can happen in a subtle way, when the runner is not aware that they aren’t eating enough to support their current activity level… We often look past this to the more stereotypical scenario of someone purposefully restricting because of a concern that their body might change. It is important to be aware of both cases so that no one slips through the cracks.

Once the runner’s energy input/output is out of balance, RED-S can set in and cause a cascade of new injuries and systemic problems. The runner in this example might then develop a stress fracture. That stress fracture then needs at least 6 weeks of no running, which in turns leads to more energy imbalance as the runner is now eating less because they’re not running at all. 

Systemic effects of RED-S are widespread.

The most commonly recognized example is the disruption in hormone function. This can affect thyroid function, and for female athletes this in turn affects the menstrual cycle and fertility. Appetite hormones and insulin are also affected, and cortisol (the stress hormone) is elevated. In men, studies have shown testosterone drops. The effects on the cardiovascular system include low heart rate, low blood pressure, and arrhythmias. Below are additional affected systems, as well as some examples of symptoms:

  • Gastrointestinal: constipation, delayed gastric emptying
  • Immune: increased likelihood of illness, typically GI or upper respiratory
  • Haematological: low iron, low hemoglobin/hematocrit, anemia 
  • Metabolic: decreased resting metabolic rate
  • Skeletal: stress fractures, osteopenia/osteoporosis, decreased muscle growth
  • Growth and development: disrupted growth hormone
  • Psychological: irritability, impaired judgment, disordered eating

A runner can experience varying levels of these symptoms, depending on the severity of RED-S. A common mix I see is: stress fractures, low iron, GI symptoms, low resting heart rate, and psychological factors.

Recovering from RED-S takes time because it requires lifestyle changes.

Medical intervention is necessary for some of the secondary conditions, but the root problem of energy imbalance needs to be addressed in the day to day life of the runner. This means changing diet, training habits, recovery habits, or (more typically) all of the above. Stress management and psychological factors also need to be addressed. (Example: working through the fear of body changes if running volume decreases.) 

These are not easy things to tackle! This is why we approach these changes in a collaborative, individual way with each runner. We expand the team as needed, and this might include a registered dietician, endocrinologist, orthopedist or a therapist/psychologist. Remember: once you’re willing to try lifestyle changes, you are already moving in the right direction. 

By Cat Fitzgerald PT, DPT, CSCS

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