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

NCT07481578 | Recruiting

• 2 other identifiers: B32220240015161172825N
• Study Type: interventional
• Target: 45
• Locations: 1 country
• Sites: 1

Brief Summary

The goal of this study is to learn how different amounts of supervised indoor cycling training change gut health (gut bacteria, the substances gut bacteria make, and the gut barrier integrity), and how these changes relate to changes in fitness, muscle health, and signs of doing too much training (a state called 'overreaching'). The study includes healthy, recreationally active men aged 18 to 45 years. The primary questions, for which the study is powered (sufficient participants included), are:

• A control group that does not complete structured training;
• A moderate-load training group that completes eight weeks of supervised cycling (4x/week);
• A high-load training group that completes four weeks of moderate-load training followed by four weeks of higher training load (twice the number of training sessions). Participants will:
• Be randomly assigned to one of the three groups;
• Complete 8 weeks of supervised indoor cycling sessions if assigned to a training group;
• Complete four study assessment periods (baseline, after week four, after week eight, and after a short taper (rest period);
• Provide blood, stool, skeletal muscle, urine, saliva, and breath samples during the assessment periods;
• Complete fitness and performance tests and questionnaires during the assessment periods.

Conditions

Anthropometric Measurements; Metabolic Health; Exercise; Overreaching; Butyrate; Gut Microbiome; Exercise Performance; Skeletal Muscle; Glucose Tolerance; Hormones; Vascular Health; Muscle Adaptation; Physical Fitness; Heart Rate Variability (HRV); Food Intake

Keywords

Exercise training; Training load; Overload training; Fecal butyrate; Gut health; Exercise performance; Muscle phenotype; Physical fitness; Overreaching; Glucometabolic health; Vascular health; Muscle adaptation; Heart Rate Variability (HRV); Anthropometrics; Metabolic health; Food intake

Outcome Measures

Primary Outcomes (2)

• Serum butyrate concentrations

  Diet and in particular fiber intake will be standardized for three days prior to and during the assessment days during which venous blood sample collection will take place. To promote microbial SCFAs production, participants will consume 15 g of oligofructose five hours prior to venous blood sample collection. Serum butyrate concentration will be assessed using gas chromatography-mass spectrometry.

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

• Fecal butyrate concentrations

  Diet and in particular fiber intake will be standardized for three days prior to and during the assessment days during which fecal collection will take place. Participants will be asked to collect a stool sample at the first experiment assessment day. Fecal butyrate concentration will be assessed using gas chromatography with flame ionization detection.

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

Secondary Outcomes (28)

• Short-chain fatty acids

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

• Gut microbiome

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

• Gut barrier

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

• Self-reported stool consistency, bowel movement frequency, and gastrointestinal distress

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

• Aerobic exercise performance

  At baseline (T1), mid-intervention after four intervention weeks (T2), post-intervention after eight intervention weeks (T3), and 10 days following intervention completion (T4).

Study Arms (3)

Control group

PLACEBO COMPARATOR

Participants allocated to the control group do not perform a structured training program. To control for expectancy effects, they receive a supervised weekly placebo capsule (1 g granulated sugar) presented as a 'novel plant extract' purported to support gut health and performance. Participants are asked to maintain their habitual exercise and dietary intake patterns and to monitor relevant behaviors as instructed.

Dietary Supplement: Supplement

Moderate load training group

EXPERIMENTAL

The moderate load training group will enroll in eight weeks of supervised moderate load cycling training.

Behavioral: Moderate load exercise training

High load training group

EXPERIMENTAL

The high load training group will enroll in four weeks of supervised moderate load cycling training followed by four weeks of supervised high load cycling training.

Behavioral: High load exercise training

Interventions

Supplement DIETARY_SUPPLEMENT

The nature of the intervention does not allow blinding of study participants. However, to induce an 'expectancy-effect' in the control group, participants allocated to the control group will receive dietary placebo supplementation. Participants will be told (deceived) that this novel 'plant extract' is believed to have the potential to mimic training effects on gut health and exercise performance. The dietary placebo capsule will consist of 1 g sugar. Intake of the dietary placebo capsule will take place after a fasting state of six hours or more, at a fixed timepoint once a week, and under direct supervision of a research investigator (Sofie Engelborghs). The control group does not participate in any study-related training sessions, but will be asked to continue and monitor (Polar Pacer heart rate monitor) their normal physical activities and sports.

Also known as: CON

Control group

Moderate load exercise training BEHAVIORAL

The moderate load training group will enroll in an exercise intervention of 8 weeks. This intervention consists of cycling sessions on an electromagnetically braked ergometer under direct supervision of the investigators at the Exercise and Muscle Physiology Group. Training intensities are prescribed based on the power output associated with the first and second lactate threshold and maximal power output obtained during a maximal incremental step test with capillary lactate measurements. Three types of training sessions will be prescribed: moderate-intensity continuous training (2x/week), high-intensity interval training (1x/week), and sprint interval training (1x/week). The training load will gradually increase over time, by increasing the session duration and/or intervals.

Also known as: MOD

Moderate load training group

High load exercise training BEHAVIORAL

Participants allocated to the high load training group will conduct a similar intervention as the moderate load training group, but with double the amount of training sessions (8x/week) throughout the last four weeks of the 8-week training program. The four weeks of high load training aims to induce a state of overreaching in some though not all participants allocated to the high load training group.

Also known as: HIGH

High load training group

Eligibility Criteria

• Age: 18 Years - 45 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• 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.

You may not qualify if:

• 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.

Sponsors & Collaborators

• Stefan De Smet: lead
• KU Leuven: collaborator
• Universiteit Antwerpen: collaborator

Study Sites (1)

Exercise Physiology Research Group, Department of Movement Sciences, KU Leuven, Leuven, Belgium

Leuven, Vlaams Brabant, 3001, Belgium

RECRUITING

MeSH Terms

Conditions

Motor Activity

Interventions

Dietary Supplements

Condition Hierarchy (Ancestors)

Behavior

Intervention Hierarchy (Ancestors)

Food; Diet, Food, and Nutrition; Physiological Phenomena; Food and Beverages

Study Officials

• Stefan De Smet, Professor

  Exercise and Muscle Physiology Research Group, Department of Movement Sciences, KU Leuven, Leuven, Belgium

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Stefan De Smet

CONTACT

+32 16 37 64 87; stefan.desmet@kuleuven.be

Sofie Engelborghs

CONTACT

+32495158699; sofie.engelborghs@kuleuven.be

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: DOUBLE
• Who Masked: INVESTIGATOR, OUTCOMES ASSESSOR
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR INVESTIGATOR
• PI Title: Professor doctor Stefan De Smet

Model Details: Participants (n = 45) will be randomized in a 1:1:1 ratio to (i) eight weeks of dietary placebo supplementation followed by 10 days without placebo supplementation (CON; n = 15), (ii) eight weeks of moderate load cycling training proceeded by 10-day taper period (MOD; n = 15), or four weeks of moderate plus four weeks of high load (overload) cycling training proceeded by 10-day taper period (HIGH; n = 15). Participants will be randomized using a computer-generated randomization sequence uploaded to a secure web application (REDCap) which conceals the randomization sequence for all researchers.

Study Record Dates

• First Submitted: February 4, 2026
• First Posted: March 19, 2026
• Study Start: October 7, 2024
• Primary Completion (Estimated): May 31, 2027
• Study Completion (Estimated): May 31, 2027
• Last Updated: March 19, 2026

Record last verified: 2026-03

Locations

BE (1)