Effect of Probiotic Supplementation on Exercise Metabolism During Exercise in the Heat and Subsequent Effect on Gastrointestinal Disturbance and Gut Microbiome Composition

Study design

Participants The study is open to well-trained endurance 18-50 years (n = 24). Participants will be invited to take part in a matched-pairs design supplement intervention study. Participants will be split into two groups (n = 12), one which will supplement with a probiotic, the other a placebo, for 4 weeks.

Initial assessment During the first visit, subjects will first be asked that the have read the participant information sheet, including that they fit the inclusion criteria. Participants will then be asked to complete the Readiness to Exercise Questionnaire to ensure there are no contraindications before they proceed to exercising, such as a musculoskeletal injury or any medical condition for which exercise would pose an above normal risk (e.g. heart condition). Subjects will complete an incremental cycling test to volitional exhaustion to assess VO2max and blood lactate profile. Briefly, section 1 will commence at 95W and each stage will increase by 30W every 3 min. The wattage will continue to increase until the blood lactate concentration increases beyond 4mmol·L-1. The blood LT will be defined as the second abrupt increase of blood lactate concentration around 4mmol·L-1 by means of a linear-regression break point analysis. In the last 30s of each stage, heart rate (Polar Electro, Finland) will be recorded and a capillary blood sample (fingertip) will be obtained for blood lactate concentration analysis by micro-assay (Lactate Pro LT-1710, ArkRay Inc., Kyoto, Japan). This initial stage will be followed by a 15 min recovery period. Section 2 of the test protocol will then commence at 3.33 w/kg-1 for 150 s and thereafter will be increased by 50 W for a further 150 s. Subsequently, increases of 25 W every 60 s will occur until volitional fatigue or a drop in cadence below 70 rev/min-1. VO2max will be determined as the highest 30 s VO2 consumption.

After completing the initial VO2max test to determine exercise intensity and resting for 30-60 minutes, subjects will complete a familiarisation session during which they will cycle at the prescribed power output for 90 minutes followed by the time to exhaustion trial. This session will be used to familiarise subjects to the procedures of using a rectal thermometer, heart rate monitor, fluid consumption during exercise, exercise capacity test, and the timings of these throughout the experimental trial. The session will also be used to assess, and if necessary, adjust the velocity to attain the required 90% lactate threshold (~70-80% VO2max intensity).

Experimental trials On the morning of the main experimental trials at ~08:00, participants will report to the laboratory in a fasted state. A baseline blood (6 mL) and breathe sample will be collected before participants are provided with a standardized high-CHO breakfast (CHO: 2 g.kg-1 BM; PRO: 0.4 g.kg-1 BM; Fat: 0.2 g.kg-1 BM; comprising cereal, milk, orange juice, and a cake bar. This is representative of an elite real-world cyclists 'Race-day" breakfast (see Table 3.3) (Heikura et al., 2019; Muros et al., 2019; Morton, unpublished observations; Sánchez-Muñoz et al., 2016). Blood samples (6 mL) will be taken 15,30, 60, 90, 120, min postprandially via an indwelling cannula. Subjects will then be fitted with a heart rate monitor (Polar Electro, Finland) and be asked to measure nude body mass (SECA, Hamburg, Germany) in private. It will be explained to the participant that they need to weigh themselves in only their underwear and they will be shown to a private room in order to do this.