Impact of Training Load on the Gut miCrobiome And Its Relation to exeRcise Performance, mUscle Phenotype, and markerS of Overreaching in Healthy Men

Inclusion criteria: * Males between 18 and 45 years old. * Recreationally active individuals, with a weekly exercise training volume between one and six hours per week. * Good health status confirmed by a sport medical screening, which includes a sport medical questionnaire and resting electrocardiogram. * Body Mass Index (BMI) between 18.5 and 27.5 kg/m². * Masters the Dutch language. Exclusion criteria: * Engagement in strenuous competitive sports one month prior to or during the study intervention. * Medication and vaccination: Pro- or antibiotic treatment during the past three months, non-steroidal anti-inflammatory drugs (NSAIDs) or cholestyramine during the past month, drugs interfering with intestinal permeability (e.g., prokinetics, laxatives, lubiprostone, loperamide, anti-spasmodics, linaclotide, proton pump inhibitors) during the past month. Vaccinations within one month prior to or during the study intervention. * Blood donations within three months or plasma donation within one month prior to or during the study intervention. * Inflammatory bowel disease (Crohn or colitis ulcerosa) or celiac disease. * Diagnosed irritable bowel syndrome. * Intake of any performance-enhancing medication or nutritional supplements known to modulate the gut microbiome in the two months prior to or during the study. * Substance abuse, including alcohol consumption of more than three units/day (weekly average). * Any injury or pathology considered a contraindication for performing physical exercise, as determined by the medical doctor overseeing the preparticipation medical screening. * No access to smartphone and/or computer with internet access. * No willingness to use the Polar Flow app and MijnEetmeter to collect physical activity, heart rate, sleep, and food intake data. * Concomitant participation in another interventional trial, without approval from the research team. * Any other reasons considered by the research team that the participant will not complete the study.