Can nutritional supplementation enhance molecular pathways responsible for building muscle following anterior cruciate ligament (ACL) injury?

Magnetic Resonance Imaging (MRI) scans will be completed using a 3Tesla imaging system. Muscle volume of all lower limb muscles will be determined for both limbs using an automated segmentation platform at the beginning of the trial, prior to intervention. MRI Scans will be performed during each participant’s familiarisation visit, prior to nutrition and exercise interventions. Each participant will undergo a single MRI of both lower limbs that will take 30 minutes in total. Participants will be escorted to Swinburne Neuroimaging by research staff, with MRIs supervised by an experienced radiographer at Swinburne Neuroimaging (Swinburne University). The evening prior to each experimental trial, participants will be provided a standardised meal to consume and be asked to arrive to the laboratory after an overnight fast (~8-10h). Participants will receive their standardised meal following their MRI at Swinburne University, comprised of chicken breast tenders/canned tuna/tofu, steam fresh carrot, cauliflower & broccoli, medium grain brown rice and butter. Each participant will undergo unilateral leg-press 1 repetition maximum (1RM) testing once only, at their initial familiarisation visit, following their MRI. 1RM will be determined for both the injured and uninjured limb. A single 1RM test will be performed, supervised by trained research staff. Each limb will complete a warm up with load equivalent to 5 on a 10 rating of perceived exertion scale for 3-5 repetitions. Load will incrementally increase (by approx 5-20kg) and repetitions will decrease until the load an individual cannot successfully lift for 1 repetition is found. 1RM testing will take approximately 15 minutes to complete. 12 muscle biopsies in total will be obtained per participant; 1 pre exercise biopsy and 1-hour post exercise, and 3-hours post exercise from each leg. This will be repeated for each of the two supplement conditions (whey protein or placebo). Additionally, 6 small blood samples (12mL each) will be collected, pre and 1-hour and 3-hours post exercise for each of the two supplement conditions. Supplementation: Immediately following leg press exercises, participants will consume 0.4g/kg body weight of whey protein isolate or an isocaloric placebo. Acute strength training intervention: Acute strength training will commence 15 minutes after resting muscle biopsies. Participants will complete a warm up of 10 reps on each leg with no load, before commencing the strength training intervention. In total, the intervention will run for 30 minutes, supervised by trained research staff. All participants will perform 6-8 sets of 8 repetitions of unilateral leg press exercise with load equivalent to 80% 1RM for each leg. Each set will be completed 1 leg at a time with limbs completing sets in alternating order. Each limb will be given 90sec rest between sets. Shortly after the final muscle biopsy sampling and completion of experimental exercise session participants will be offered a light snack (e.g. muesli bar). The washout period between each intervention will be no more than one week between experimental conditions.