The aim of this randomized 5-arm clinical trial is to evaluate the effect of combined anabolic interventions compared to single or placebo interventions on physical performance in community-dwelling (pre)sarcopenic elderly (≥ 65 years) living in Belgium. Physical performance will be evaluated using the Short Physical Performance Battery (SPPB). Muscle mass will be measured using a dual energy x-ray absorptiometry (DXA) and/or bioelectrical impedance analysis (BIA). Muscle strength will be measured by the Biodex (knee-extensor and knee-flexor) and a 1 hand-held dynamometer. The trial will also determine the underlying mechanisms of action using blood measures (such as markers of inflammation and sarcopenia) and muscle biomarkers. Important secondary outcome measures are compliance to the exercise program and to the protein and omega-3 supplementation, as well as functional, cognitive and nutritional status and the patients report on benefits and adverse events.

The study consists of four parts. Part I is the screening phase, which starts from the moment the participant has signed the informed consent until the start of the preparations of the study. During the screening, participants will be assessed for study eligibility by the study coordinator and contributors. If the participant is eligible, he or she will be randomly assigned into 1 of 5 intervention groups: Group 1: Exercise intervention; Group 2: Protein supplement; Group 3: Exercise intervention + protein supplement; Group 4: Exercise + Protein supplement + omega-3 supplement; Group 5: No intervention.

Part II is the preparation phase, in which the participants starts some of the interventions before the start of the study to familiarize patients with e.g. the intake of a protein supplement. All the participants will take an oral vitamin D supplement (800 IU cholecalciferol) from 4 weeks before the start of the intervention if their vitamin D level is above 20 nmol/L. Patients with a vitamin D level \< 20 nmol/L will receive repletion therapy. A trial diary will be completed by all participants to record PA, falls and intake of protein/omega3/placebo and vitamin D products. Participants in the exercise intervention (group 1, 3 and 4) will be invited to an information session where the Otago Exercise Program (OEP) will be explained and practiced. With respect to the protein supplementation, participants will receive an individually adapted protein supplement to achieve the recommended total daily intake of 1.5 g protein/kg. This will be realized by adding an individualized amount (g) of protein powder during breakfast, lunch, dinner or snack between, before or after meals, based on the subjects' food intake assessed by a food diary. The protein powder is commercially available and consists of 4.5g protein/ 5g powder. The participants in group 2, 3 and 4 will start taking the protein supplement or matched placebo 5 days before the start of the intervention. Four weeks before the start of the intervention, the participants of group 4 will start with the intake of omega-3 (1 capsule providing in total 500 mg eicosapentanoic acid (EPA) and 450 mg docosahexaenoic acid (DHA)) or matched placebo. Placebo will be provided for the participants who are not given a protein and/or omega-3 supplement. Participants are blinded to the nutritional interventions.

The third part of the study, the intervention period, takes 12 weeks. During this period, there are 8 contact moments (at baseline, week 1, week 2, week 4, week 6, week 8, week 10 and week 12). All the participants continue with the vitamin D supplementation. Participants in the exercise intervention (group 1, 3 and 4) will perform the optimized and personally adapted OEP and will also follow a walking plan. The strength exercises of the OEP are personalised based on the individual's 1 repetition maximum. Balance exercises of the OEP are personalised based on improvements on MiniBESTest scores during the intervention period. The nutritional intervention groups (protein supplementation: group 2, 3 and 4 and omega-3 supplementation: group 4) continue with the protein and/or omega-3 supplements until the last visit of the intervention period.

Part IV is the follow-up period, after the intervention. This phase takes 12 weeks and exists of 2 telephone contacts and 2 contact moments. All the participants continue the vitamin D supplementation until the last visit of the follow-up. The exercise intervention group (group 1, 3 and 4) may continue the OEP, but no personal encouragement will be given during this period. No protein and/ or omega-3 supplements will be given during the follow-up.

Several outcomes will be measured during the contact moments of the intervention period and follow-up period (part III and part IV). This will be done by questionnaires about nutritional status, fall history and use of health care (from baseline until end of follow-up), and evaluation of functional and cognitive status. Blood, urine and muscle samples will be taken. The physical activity will be measured by wearing a movement tracker. All participants will wear a movement tracker 5 days before the intervention period and during the first two weeks of the intervention period and last two weeks of the intervention period, and during the last 2 weeks of the follow-up period. Participants who receive an exercise intervention (group 1, 3 and 4) will be encouraged to wear the movement tracker during the complete intervention period. The participants will complete a four-day food diary throughout the trial at week 1, week 6, week 12 and week 24. The participants will be asked for compliance during the preparation period and intervention period and their fall history which can be monitored by using diaries during the intervention period and the follow-up period.

Addendum 27-07-2021: starting from 01-2021 a substudy was initiated in which participants of ENHANce, who agreed for participation in this substudy, collect stool samples at baseline, week 4, week 8 and week 12 of the intervention. This will allow to observe possible changes in gut microbiota composition and intestinal inflammation.