The LEAP Study: Longitudinal Effects of protein beverage and Activity on muscular Performance in physically inactive older adults.

This trial will include two intervention groups. Participants in both groups will complete the same 12-week structured resistance training exercise program, with the beverage intervention differing between groups. Group 1: Multi-ingredient high-protein beverage combined with resistance training Participants allocated to Group 1 will receive a daily multi-ingredient high-protein beverage intervention in combination with the structured resistance training exercise program. The multi-ingredient high-protein beverage was formulated in collaboration with an Australian food company at its Development and Innovation production facility. The beverage contains 10% protein derived from a blend of dairy- and plant-based protein sources, in addition to essential vitamins and minerals. Intervention dose (250 mL/day): Energy: 926 kJ Flavour: Chocolate Group 2: Low-protein beverage combined with resistance training Participants allocated to Group 2 will receive a daily low-protein beverage intervention in combination with the same structured resistance training exercise program. The low-protein beverage is commercially available and contains a lower protein composition (0.6%). Intervention dose (250 mL/day): Energy: 425 kJ Flavour: Chocolate Beverage Intervention Protocol Participants will consume 250 mL of their allocated beverage (either the multi-ingredient high-protein beverage or the low-protein beverage) once daily for 12 weeks. The beverage will be consumed between meals, without intentional modification to participants’ habitual dietary intake. Both beverages are ready-to-drink products. Participants will be instructed to consume the entire 250 mL dose at a time of their choosing during the day as a snack between meals. The beverage may be consumed at any time throughout the day; however, only one 250 mL dose will be consumed daily. Adherence to the beverage intervention will be monitored using participant-completed daily intake questionnaires and verified through the weekly return of used beverage packaging. Resistance Training Exercise Intervention All participants will complete a 12-week resistance training exercise program conducted at a public gym facility. Exercise sessions will be performed twice weekly on non-consecutive days, with each session lasting approximately 40 minutes. The first two exercise sessions will be supervised by an Accredited Exercise Physiologist to familiarise participants with the exercise protocol, ensure correct exercise technique, and promote safe participation. Following this familiarisation period, participants will independently continue the exercise program developed by the Exercise Physiologist using either an exercise program booklet or a mobile phone-based application. The resistance training program will include a warm-up, resistance exercises targeting major upper and lower body muscle groups, and a cool-down. The exercise program will consist of: Upper body exercises: Lateral pulldown Chest press Lower body exercises: Leg press Hamstring curl Knee extension The 12-week resistance training program will be structured into four progressive phases: Weeks 1–3: Foundation phase 2 sets per exercise 6–8 repetitions per set Target RPE: 4–6 (CR10 scale) Weeks 4–6: Build phase 2 sets per exercise 6–8 repetitions per set Target RPE: 6–8 (CR10 scale) Weeks 7–9: Power phase 3 sets per exercise 8 repetitions per set Target RPE: 6–8 (CR10 scale) Weeks 10–12: Peak phase 3 sets per exercise 8 repetitions per set Target RPE: 6–8 (CR10 scale) Resistance training loads will progressively increase throughout the intervention period. Load progression will involve an approximately 2% increase for upper-body strength exercises and a 10% increase for lower-body strength exercises. Adjustments to training loads will be determined based on participants’ perceived exertion following completion of each training phase to ensure appropriate progression of exercise intensity. Participants will be familiarised with the CR10 Rating of Perceived Exertion (RPE) scale and the target RPE required following each exercise session. During the final week of each training phase, the Principal Investigator will review participants’ reported RPE to confirm adherence to the prescribed training intensity and progressive loading protocol. Adherence to the exercise intervention will be assessed through gym attendance records, based on participant sign-in records collected at each exercise session.