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:
1. Does moderate load training change blood and faecal levels of butyrate (a short-chain fatty acid made by gut bacteria) after eight weeks compared with a control group?
2. Compared to moderate load training, do higher training loads lead to different responses in blood and faecal levels of butyrate?
Researchers will compare:
* 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.