Hello Laurens,

As you have discovered, this is not uncommon and there has been a lot written about it, from the 'blog' type sites to the more academic. These papers might be of interest:

De Oliveira, E. P., & Burini, R. C. (2009). The impact of physical exercise on the gastrointestinal tract. Current Opinion in Clinical Nutrition & Metabolic Care, 12(5), 533-538.

https://www.researchgate.net/publication/26300953_The_impact_of_physical_exercise_on_the_gastrointestinal_tract

Shephard, R. J. (2015). How fast must you trot? Vigorous exercise and diarrhoea. The Health & Fitness Journal of Canada, 8(1).

http://new-hfjc.library.ubc.ca/index.php/html/article/download/185/156

Triezenberg, D., & Simons, S. M. (2010). 24 Runner’s Diarrhea. Diarrhea: Diagnostic and Therapeutic Advances, 425.

https://books.google.co.uk/books?

hl=en&lr=&id=BstHGdtpb9AC&oi=fnd&pg=PA425&dq=runner%27s+diarrhoea+why+and+treatment&ots=6GNipg675y&sig=wLoxdNv5U7l7SDxGv3nASSxOxaw#v=onepage&q=runner's%20diarrhoea%20why%20and%20treatment&f=false

I hope you find a solution that is right for you; very best wishes with your running,

Mary

Article The impact of physical exercise on the gastrointestinal tract

Hi Laurens,

to complete the listing from Mary...about nausea when running or more generally GI complains, role of the immune system (through endotoxemia), and a putative link with exertional heat stroke.

Best,

Laurent

Nausea is associated with endotoxemia during a 161-km ultramarathon

Kristin J. Stuempfle, Taylor Valentino, Tamara Hew-Butler, Frederick M.

Hecht & Martin D. Hoffman 

http://dx.doi.org/10.1080/02640414.2015.1130238

https://www.researchgate.net/publication/262050754_Gastrointestinal_Complaints_During_Exercise_Prevalence_Etiology_and_Nutritional_Recommendations?ev=srch_pub&_sg=RVXhXacXblw1ofxNx5GIjrZ2u7dH0W09jsSglJKqw6W-Brl5zfem7Gp9n_TBLWyp.oQ_TEyyXLOT-LmUwdcupnQTsYnl_HJlo_Y0C75yjF6pJS6U8K6-4_xocJcS0IEz8.eCD42tmj93z64A2eqmqhXRrbmhaOzogbT2HzOVgowfBAPIJ5c8jvXuX0kmq_SGU_

Gastrointestinal Complaints During Exercise: Prevalence,Etiology, and Nutritional Recommendations

Erick Prado de Oliveira • Roberto Carlos Burini •

Asker Jeukendrup

Sports Med (2014) 44 (Suppl 1):S79–S85

DOI 10.1007/s40279-014-0153-2

Ibuprofen Use, Endotoxemia, Inflammation, and Plasma Cytokines During Ultramarathon Competition

 David Christopher Nieman et al.,

 Brain Behavior and Immunity 20(6):578-84 · December 2006

DOI: 10.1016/j.bbi.2006.02.001 · Source: PubMed

https://www.researchgate.net/publication/7225295_Ibuprofen_Use_Endotoxemia_Inflammation_and_Plasma_Cytokines_During_Ultramarathon_Competition

The Roles of Exercise-Induced Immune System Disturbances in the Pathology of Heat Stroke The Dual Pathway Model of Heat Stroke

Chin Leong Lim and Laurel T. Mackinnon

Sports Medicine 36(1):39-64 · January 2006

DOI: 10.2165/00007256-200636010-00004

https://www.researchgate.net/publication/7329144_The_Roles_of_Exercise-Induced_Immune_System_Disturbances_in_the_Pathology_of_Heat_Stroke

Article Gastrointestinal Complaints During Exercise: Prevalence, Eti...

Article Ibuprofen Use, Endotoxemia, Inflammation, and Plasma Cytokin...

Article The Roles of Exercise-Induced Immune System Disturbances in ...

Thank you to Laurent and Mary for covering a wide range of literature to give you a sound footing in understanding the physiology of the gastrointestinal tract - particularly during exercise.  One thing that hasn't been picked up is the sheer volume of water the athletes were consuming throughout the day.  Additionally, it is not clear as to whether the training camp was conducted in a different country than the athletes were usually training in - two things to clarify before making comparisons to your own circumstances.

Finally, these are seemingly well trained athletes familiar with increased training loads - your personal circumstances suggest you are not familiar with training loads therefore making the link between the two events difficult.