Skeletal Muscle Adaptations to Peptide-Supplemented Resistance Exercise Training

The intervention involves undertaking 3 supervised, in person, training sessions per week for 8 weeks, which are designed to increase muscle mass and strength of all major muscle groups. Each session will involve performing 7 different exercises in the order of a seated chest press, standing overhead press, bent-over row, 45-degree leg press, knee extension, seated hamstring curl, and a seated calf press. For each exercise, participants perform 4 working sets to volitional failure with 75% 1RM with a two-minute rest period will be given between sets. Resistance exercise loads will be adjusted between sets to ensure that participants consistently reach volitional failure between 8-12 repetitions and reset during week 5 when interim 1RM tests are undertaken. Throughout this period, participant will consume their assigned supplement daily either in the morning on non-training days or within 30 mins of training on training days.

Participant's body composition will be determined through a full body DEXA scan before and after the intervention. They will have their height and weight determined prior to this scan to confirm their BMI and to calibrate the DEXA machine. The DEXA scan involves resting supine for approximately 20 minutes whilst the machine utilises a low dose of ionising radiation to estimate the total amount of fat mass and fat-free (lean) mass. The distribution of these is also determined across different body segments. The dosage of radiation is approximately 10 micro-Sieverts (µSv), which is far lower than the 80µSv airline passengers are typically exposed to during a single transatlantic flight. Scans will be conducted in line with IRMER regulations/guidelines by an appropriately trained individual.

Before and after the 8-week training intervention, a skeletal muscle (vastus lateralis) biopsy sample will be obtained from participants. This will be completed by a trained individual, in sterile conditions and under local anaesthetic using the Bergstrom needle technique modified for suction. These will be immediately processed and stored for subsequent analysis following intervention completion by all participants.

Before and after the 8 week training intervention, a single 10ml venous blood sample will be collected from participant's antecubital vein. Serum and plasma will be subsequently isolated from the sample and stored for future analysis.

This uses an isokinetic dynamometer to determine the peak amount of force that the leg extensor (thigh) muscles can produce during a voluntary muscle contraction. Participants will be required to sit on a padded dynameter chair with their lower legs naturally hanging over the edge of the chair, bent at a 90-degree angle. On each attempt, participants will be asked to cross their arms over their upper body and, following a count of 3 seconds, to kick as hard and as fast as possible into the stationary shin pad for 5 seconds, with peak force recorded during each attempt. This will be completed before and after the 8 week training/supplement intervention.

Participants will next complete 1RM strength tests for 7 different resistance exercises before, mid-way and after the intervention. Each exercise will target different areas of the body and will be performed throughout the 8-week training programme. These include a seated chest press, standing overhead press, bent-over row, 45-degree leg press, knee extension, seated hamstring curl, and seated calf press. This involves lifting progressively increasing loads for each exercise until a single repetition can no longer be completed with correct form. Attempts will be separated by a rest interval of 2 minutes.

Participants will have their vastus lateralis muscle thickness and cross-sectional area measured via an Ultrasound scan. They will be asked to lie still on a medical examination couch whilst a member of the research team locates the position of their greater trochanter and lateral condyle of the femur. The ultrasound probe will then be placed on this mark and repositioned vertically to identify the medial and lateral borders of the VL. The midpoint of these locations will be marked and the distance between the superficial and deep aponeuroses of the VL muscle will be measured to quantify VL muscle thickness. A wide-view image spanning the entire cross-section of the vastus lateralis will also be obtained for cross-sectional area assessment.

Participants will be asked to record a 3-day weighted food diary on weeks 1, 5 and 8 of the resistance training programme. The choice of days will be at the participants discretion but must include 2 weekdays and 1 weekend day to account for dietary variation throughout the week. On these days, they will be required to record all food and drink consumed which contains calories, including the weight/volume and branding. Food diaries will be analysed for macronutrient and caloric intake. This data will be used to determine whether participant's diets, especially protein intake, remains relatively stable throughout the interventional period. Full instructions on how to properly record a weighted food diary will be provided by the research team at the start of the training period. Depending on participant preference, diaries may be recorded physically within a provided logbook or electronically using a mobile application (MyFitnessPal). Weighing scales will be provided by the research team

In a double-blind manner, participants will be randomised to supplement or placebo cohorts. Assigned supplements will be consumed daily across the 8-week intervention either in the morning on non-training days or with 30 minutes of training on training days. The placebo will contain maltodextrin carbohydrate, whereas the supplement will comprise 5 active ingredients: 1) Dileucine (Peptide 185™, 2g/serving), 2) PeptiStrong®( 2.4g/serving), a trademarked hydrolysed Broad Bean (Vicia faba) protein extract, 3) Calcium β-hydroxy-β-methylbutyrate monohydrate (myHMB®, 1.5g/serving), a leucine metabolite in its calcium salt form, 4) Creatine monohydrate (5g/serving), , and 5) PepForm® creatine monohydrate (1g/serving), a trademarked creatine monohydrate product where creatine is bound to peptides derived from whey proteins. Supplements will be provided in opaque contained withs instructions to add one scoop (provided) of supplement/placebo to 300ml water.