How RED-S affects bones, muscles and performance
The relative energy deficit in sport (RED-S) syndrome has serious consequences for physical health and athletic performance. Endurance athletes in particular feel the effects when their energy supply is insufficient over the long term to support exertion and recovery [2][1].
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#### Reduced bone density and stress fractures
One of the most serious consequences of RED-S is a decrease in bone density. The body reacts to the energy deficit by reducing the production of hormones such as estrogen and testosterone, which are essential for bone formation. As a result, bones become more brittle, and the risk of stress fractures increases significantly. These injuries develop gradually and often lead to lengthy breaks from training [1][6].
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#### Muscle atrophy and reduced performance
Due to insufficient energy supply, there are not enough resources available for maintaining and building muscle. Furthermore, the muscles' glycogen stores, the most important energy substrate for endurance performance, are almost depleted. This leads to a significant decrease in performance, persistent fatigue, and a reduced capacity for training adaptations. Affected individuals often experience general weakness and struggle with a lack of strength and endurance [2][6].
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#### Long-term performance losses
The energy deficit also causes a change in metabolism: the basal metabolic rate decreases, and hormones such as cortisol become more active, further hindering regeneration. These biochemical adaptations cause the body to switch into an "energy-saving program," which reduces the effectiveness of training stimuli and leads to stagnation or decline in performance development. In the long term, this can make ambitious goals unattainable [1][6].
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#### Increased risk of injury and infection
The combination of poor bone quality, weak muscles, and a compromised immune system significantly increases susceptibility to injury. Frequent muscle and tendon injuries, recurring infections, and slow healing are typical accompanying symptoms. The risk of overuse injuries is particularly high because the body's regenerative capacity is severely limited [2][1].
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**Conclusion:**
RED-S leads to serious health problems that directly affect athletic performance. Understanding the links between energy deficiency, hormonal balance, and tissue health is essential for prevention and treatment to ensure that endurance athletes remain fit, injury-free, and perform at their best in the long term [2][1].
Sources
[1] RED-S https://sportaerztezeitung.com/rubriken/ernaehrung/13482/red-s/
[2] RED-S Syndrome: A Guide to Relative Energy Deficit ... https://blackroll.com/de/artikel/red-s-syndrom
[3] RED-S CAT™ https://bjsm.bmj.com/content/suppl/2015/10/14/49.7.421.DC1/RED-S_CAT_DEU_FINAL20151002.pdf
[4] RED-S: Relative energy deficiency in sports due to too much ... https://oped.de/blog/red-s-im-sport-zu-viel-training-und-zu-wenig-kalorien
[5] Relative energy deficit in sport https://de.wikipedia.org/wiki/Relatives_Energiedefizit_im_Sport
[6] Running and running injuries - RED-S https://www.theroga-physiotherapie.de/laufen-laufverletzungen-3/
[7] Recognizing & Acting on REDs - Exercise, Nutrition and ... https://www.hs.mh.tum.de/exercisenutrition/ressourcen-fuer-sportlerinnen/reds-erkennen-handeln/
[8] All about the RED-S syndrome https://www.sportslab.at/blogs/news/alles-uber-reds
[9] Young, sporty – and sick https://www.doccheck.com/de/detail/articles/43323-jung-sportlich-und-krank
[10] What I as a track and field athlete should know about the RED-S https://swiss-athletics.ch/wp-content/uploads/red_s_broschuere.pdf
