The goal of this controlled, experimental study is to learn about the effects of 10 sessions of hyperbaric oxygen therapy on physical performance, vascular circulation, biochemical parameters, and composition of the intestinal microbiota in young healthy men depending on the frequency of single treatments.

The main questions it aims to answer are:

1. Do 10 treatments of hyperbaric oxygen therapy induce significant changes in physical performance levels, vascular circulation, and concentrations of biochemical parameters in young, healthy men?
2. Does the body's response to 10 treatments of hyperbaric oxygen therapy differ depending on the frequency of treatments?
3. Does a series of hyperbaric oxygen therapy treatments induce significant changes in the composition of the intestinal microbiota, metabolome, and functional status of the intestines?

Participants are exposed to hyperoxia under hyperbaric conditions or form a control group with no treatment.

Inclusion Criteria:

• Age 18-35;
• Healthy, physically active men;
• Subject who is knowingly willing to participate in the study;
• Subject able to read, understand and sign an informed consent to participate.

Exclusion Criteria:

• Inability to attend scheduled visits and/or follow study protocol;
• Use of HBOT prior to study inclusion;
• Severe or unstable physical impairment or severe cognitive deficits at study entry;
• Pressure-sensitive chest diseases (including moderate or severe asthma) or pressure-sensitive ear or sinus diseases;
• Active smoking;
• Having suffered an injury within 3 months up to the date of the study;
• Taking pre- and/or probiotics in the last 3 months before the study;
• Inpatient hospital or emergency room stay in the last 4 weeks prior to study entry;
• Travel to tropical countries during the last 4 weeks prior to the study;
• Taking antibiotics, steroids and steroid-anabolic agents during the last 4 weeks before the study