The influence of cow or soy milk on circulating blood sex hormones following a single session of resistance exercise.

Study overview Eligible participants will attend the Illawarra Health and Medical Research Institute (IHMRI) on three occasions in total. The first visit to IHMRI will be for a maximal strength assessment (1-Repition Maximum [1-RM]). The maximal strength assessment (visit 1) will be followed by two subsequent visits to complete two identical resistance exercise training sessions where either cow or soy milk will ensue followed by blood collection (visits 2 and 3). An experienced trainer will supervise all resistance exercise sessions. Visit 1. A single testing session will be conducted at IHMRI to determine 1- repetition max strength for several resistance exercises including: barbell bench press, latissimus dorsi pulldowns, seated barbell shoulder press, standing barbell biceps curl, and seated machine triceps extension. 1-RM will be established from the best of 4 attempts at each exercise, each separated by 5 min of rest. Upon completion of 1-RM for each exercise, 10 min will be permitted before testing the next exercise. Standardised instructions on testing procedures will be provided to all participants and verbal encouragement will be offered throughout the testing session. Visit one is expected to take approximately 1.5 hours to complete Visits 2 and 3. Participants will be able to perform their usual exercise training regimen until 48 h prior to resistance exercise training sessions. All participants will complete resistance exercise training sessions at the same time of day (between 0600 and 0900) to control for diurnal hormonal fluctuations. Participants will begin with a warm-up consisting of 2 sets of 20 repetitions for barbell bench press at 40% of their predetermined 1-RM load. Three sets at 70% of 1-RM will then be completed for the same exercises used in the maximal strength assessment: barbell bench press, lat pulldown, seated dumbbell shoulder press, standing barbell biceps curl, and seated machine triceps extension. Participants will be instructed to perform repetitions until voluntary exhaustion, and verbal encouragement will be provided. Pausing between the eccentric and concentric phases of each repetition will not be permitted. There will be 2 min of passive rest between each of the sets of exercises (barbell bench press, latissimus dorsi pulldown, seated dumbbell shoulder press, standing barbell biceps curl, and seated machine triceps extension) and 2 minutes of passive rest between each exercise. Session attendance checklists will be completed at visits 2 and 3 to monitor training output. The second resistance exercise training condition, which is identical to the first will proceed within 7 days after completion of the first. Visits 2 and 3 are anticipated to take approximately 3 hours to complete. All subjects will be asked to maintain their usual activities of daily living throughout the study. Participants will consume either soy or cow's milk following both visits 2 and 3 and have blood samples collected to test their reproductive hormone levels (details below). Nutritional intervention Utilising a randomised crossover design, all subjects will complete each treatment condition: dairy milk and soy milk following resistance exercise (70% of 1 repetition maximum). The dairy milk will be organic, grass-fed, locally procured whole milk. Soy milk will also be organic. A single serve of 600 mL/m2 of milk will be provided, a quantity administered in previous research yielding 33-40g protein. Milk will be provided at 45 minutes post-exercise and all milk will be consumed within 10 min to ensure intake within the “post-workout anabolic window of opportunity,”. A registered dietitian will provide the nutritional intervention (soy or cow’s milk) to participants. Participants will be instructed to continue with their habitual dietary patterns 2 days prior to each visit and will be advised on how to record all food items consumed including the amounts and recipes. A registered dietitian will be available to answer questions as needed throughout the food diary collection periods. Intake of dairy (including dairy from cow, goat, and sheep) and soy products as well as alcohol and more than 1 cup of coffee per day will be prohibited for 2 days prior to each experimental condition and the investigators will emphasise the importance of abstaining from supplements and ergogenic aids throughout the course of the study. The ‘Meallogger’ smartphone application will be used to assess/monitor participants adherence to the nutritional restrictions. Participants will be instructed to refrain from food consumption for 12 h prior to each experimental condition. Water consumption will be permitted however, in order to maintain euhydration. Hormone testing and analysis At both resistance exercise training sessions (visits 2 and 3) blood samples will be obtained to quantify the plasma concentration of selected sex hormones (total testosterone, progesterone and estrogen) immediately following exercise and at additional time points. Approximately 4 mL of blood will be drawn from the antecubital vein and will be collected with subjects in a seated, slightly reclined position upon exercise completion and 30, 45, 60, 80, 100, 120 min thereafter following milk consumption. Samples will be centrifuged at 3500 rpm at 4°C for 10 min for separation of plasma, which will be aliquoted and stored at -80°C with 1 thaw for analysis. Plasma hormone levels will be measured in duplicate by Cardinal laboratory.