The study will evaluate the change in gastrointestinal (GI) flora following probiotic supplementation, and expected to lead to an increase in the intestinal epithelial integrity and to improvement in its health. Concurrently with the reduction in the amount of toxins in the GI tract following an intensive exercise, a lower incidence of symptoms of discomfort will improve the quality of the training sessions which will be exhibited by an improvement in endurance capacity and in physiological responses to rigorous exercise. Half of the participants will receive probiotic supplement while the other half will receive a placebo.

Masters runners and professional competitive cyclists will be recruited, as follows: 30 young road cyclists ages 18-39 years, 60 masters runners ages 40-60 years

Sample Size: 90 subjects will be recruited, following the first set of tests and experiments will randomly be divided into two matched groups experimental and experimental groups. The rational for sample size calculation is based on detecting a defined effect size with 5% statistical significance and 80% power. Effect size reflects the difference in the treatment effect between the groups will be calculated as the difference in measurement values between the experimental (probiotics) and control (placebo) groups divided by the standard deviation. Cyclists' cohort will include 34 subjects which will demonstrate effect size of 1.0. Masters runners' cohort will include 60 subjects which will demonstrate effect size of 0.75.

Study design: A random double-blind prospective study

Recruitment of participants will be executed by study staff which will also serve as trainers of cycling and running groups in Israel's Upper Galilee area.

Subsequently to signing on an informed consent form with one of the study physicians, participants will complete the following procedures:

• A series of preliminary tests (Anthropometry, Maximal Oxygen Consumption, Endurance tests) will be conducted by one of the study physicians from Ziv Medical Center in Zefat
• Food Frequency Questionnaires (FFQ ) and frequency of GI symptoms will be completed electronically with Qualtrics (Qualtrics LLC, Provo, UT, USA)
• Blood samples (approximately 10 ml of venous blood) for quantifying immune factors (inflammation) will be collected at Ziv Medical Center or at Tel Hai Academic College and will be sent to the molecular microbiology and biotechnology laboratory in Tel Aviv University.
• Stool samples for testing the genetic expression of the microbiome composition. The tests will be delivered to the study staff at Tel Hai University and after freezing them, they will be sent together in dry ice to the molecular microbiology and biotechnology laboratory in Tel Aviv University
• Tests for evaluating aerobic endurance (Lactate Threshold - cyclists, running economy or time to fatigue - runners) will be conducted at the exercise physiology laboratory in Tel Hai College.

After the completion of tests, participants will randomly be divided to 2 matched groups according to the level of physical fitness, and age in a double-blind design. The experimental (E) group will be given probiotic supplement in capsule form whereas the control (C) group will be given placebo capsules identical in size and color to the probiotic ones.

The participants will consume the supplement / placebo capsules during a period of 90 days after which they will return for an additional visit in which they will re-complete questionnaires and will undergo identical tests and procedures which they had completed during their first visit (before the assignment into groups).

Inclusion Criteria:

• age 18-60 years
• at least 3 years of national-level experience, including participation in competitions
• suffer from one or more of the following symptoms: nausea, vomiting, belching, heartburn and chest pain, bloating, cramps, side pain, urge to empty bowels and diarrhea during training and competitions

Exclusion Criteria:

• Diagnosis of gastrointestinal diseases
• Diagnosis of heart diseases
• Use of Probiotics during the 3 months' period prior to the study
• Use of Antibiotics during the 3 months' period prior to the study
• A radical surgery in the digestive system during the year prior to the

Anonymous individual subjects data for all outcome measures will be made available within 12 months of study completion