Performance and metabolic effects following a single course of antibiotic treatments in healthy individuals

1.1 Overview The study will adopt a single-arm trial design, using pre- and post-outcomes to test the hypotheses. Eligibility and health screening questionnaire will be conducted by phone. Participants will attend three laboratory sessions at Murdoch University physiology laboratory; a familiarisation session with VO2peak assessment, and two experimental sessions with no less than 5 days separating sessions. Familiarisation session will used to familiarise participants with the equipment and the time-trial adopted within the study and attain lactate values of corresponding power outputs for experimental sessions. 1.2 Procedures 1.2.1 Familiarisation session and VO2peak Participants will attend following an overnight fast >10hrs to best replicate testing conditions. Following collection of height and body mass, participants will complete a maximal aerobic performance test (VO2max), using an electromagnetically braked Velotron cycle ergometer (Racermate, USA). Expired ventilation will be collected continuously using a metabolic cart (TrueOne 2400, ParvoMedics, USA). All participants will start at a workload of 50W which will be increased by 35 W every two minutes. Finger-stick lactate will be collected in the final 30 seconds of each stage. Once RER has reached 1.0, workload (35W) will be increased every minute until volitional exhaustion. From this a work output corresponding to a blood lactate of 3mM will be calculated for use in the constant-work component in the experimental sessions. Participants will then be familiarised with the time-trial, which will begin ~20 minutes after completion of the VO2max test. The time-trial will be based on completion of a caloric goal, which will be standardised at 400 Calories for all participants. Participants are able to self-select their cadence as well as gearing and will be able to adjust these throughout the time-trial. Participants will be able to consume water ad libitum before and during the time trial. 1.2.2 Experimental Trials Both experimental trials will be conducted in the morning following an overnight fast >10hrs. Participants will be asked to maintain a 72-hour food and exercise diary prior to the first experimental trial. Normal exercise may be continued leading up to the first experimental trial and participants should best replicate the diary conditions leading up to the second experimental trial. Heavy training in the 24 hour period immediately prior to trials will be discouraged. Each trial consists of a 60 minute steady state (fixed power) cycling at power output corresponding to 3mM of lactate on a Velotron cycle ergometer (Racermate, USA), followed immediately by a time trial for 400 calories. Gas exchange data will be collected using a metabolic cart during the fixed power cycling (TrueOne 2400, ParvoMedics, USA), with heart rate date collected using a heart rate monitor (Garmin, USA). Ratings of perceived exertion (RPE) will be collected using the 6-20 Borg scale (10) and measured every 15 min during fixed power exercise, and every 5 min during the time trial and 5 minutes post completion. During the time-trial, only heart rate and RPE will be collected at each 100 Calorie point. Following experimental trial one, participants will be asked to commence a five-day course of oral Cephalexin 500mg, with dosing as 06:00, 12:00, 18:00, and 20:00. First dose should commence at 12:00 on day one, with the final dose taken at 06:00 on the day of experimental trial two (Day 6). Participants will be monitored in the laboratory for one hour post administration of the first dose to assess for serious side effects (11). Adherence to the Cephalexin dosing will be monitored through a diary and participants will receive two text messages during the 5-day course as a reminder. At the completion of experimental trial two, participants will be asked regarding compliance and report whether any doses were missed. 1.2.3 Blood sampling and analysis Blood sampling in each trial will occur from a cubital fossa vein. A 20 gauge peripheral venous cannula will be placed using sterile technique. 4ml of blood will be collected via using lithium heparin vacutainer tubes. The cannula will be flushed with 10ml 0.9% saline after each sample is taken. 4mL of blood will be taken and discarded prior to collection of sample two and three to ensure no saline remains in the cannula. Samples will be taken prior to commencement of activity, after the fixed output session, and immediately after the completion of the time trial. Testing and sampling will be completed by Dr Ewan Smith, medical doctor 8 years. Laboratory supervision by Associate Professor in Exercise Physiology Timothy Fairchild. Ethics approval is has been applied for with the Murdoch University Human Research Ethics Committee.