Referred to general practitioner (GP) for further follow-up. The GPs will be informed about participants sarcopenia status with results from assessments of muscle strength, muscle mass, and physical performance. The management of the sarcopenia is at the GPs own discretion.

Number of falls requiring medical attention. Collected via self-report and ascertained by linkage to the Norwegian Patient Registry and medical journals with the use of unique 11-digit Norwegian national identification number for each participant.

Classified according to the International Classification of Diseases, 11th revision, classification system. Peripheral fracture rate per person-years, number of peripheral fractures, number of people sustaining peripheral fractures, and number of people sustaining multiple events. Collected via self-report and ascertained by linkage to the Norwegian Patient Registry and medical journals with the use of unique 11-digit Norwegian national identification number for each participant.

1-repetition maximum leg press and leg extension

Maximal isometric handgrip strength

Muscular power assessed using a force platform installed on a leg press machine

Physical performance using the Short Physical Performance Battery

Static and dynamic balance using the Mini-Balance Evaluation Systems Test (BESTest)

Stretch stature using a wall-mounted stadiometer

Body mass estimated using multi-frequency bioelectrical impedance analysis

Estimated using multi-frequency bioelectrical impedance analysis. Fat mass, skeletal muscle mss, appendicular skeletal muscle mass.

Waist, arm, and calf circumference

Systolic and diastolic blood pressure, and resting heart rate measured after 5 minutes of seated resting using an automated blood pressure device

Systolic and diastolic blood pressure response 1, and 3-min after standing up

Self-reported physical activity levels

Health-related quality of life assessed using the 12-item Short-form health survey

Fear of falling assessed using the Falls Efficacy Scale-International

Cognitive function evaluated using The Mini Mental State Examination

Levels of depression measured via the Geriatric Depression Scale.

Physical frailty assessed according to Fried's frailty phenotype

Nutritional status assessed using the Mini-nutritional Assessment Short form.

Sleep quality assessed using the Pittsburgh Sleep Quality Index

Information about hospitalisations due to falls and fall-related injuries will be collected by means of electronic linkage to the Norwegian Patient Registry and medical journals with the use of a unique 11-digit Norwegian national identification number for each participant.

Use of primary health care (general practitioner, emergency room, physiotherapist, and chiropractor), community care, and assistive technology during the study will be collected by linkage to the Norwegian Municipal Patient and User Register (KPR) database with the use of a unique 11-digit Norwegian national identification number for each participant.

Use of prescription drugs during the study will be collected by linkage to the Norwegian Prescribed Drug Registry with the use of a unique 11-digit Norwegian national identification number for each participant.

DFS is defined as time from randomization to the first occurrence of: (i) death from any cause; (ii) incident dementia; or (iii) incident ADL disability. Participants with dementia or ADL disability at baseline are excluded from the DFS analysis.

Death: ascertained by linkage to the Norwegian Cause of Death Registry.

Incident ADL disability: score of 3-5 any of the six primary ADLs (Physical Self-Maintenance Scale) or a score of 0 for any of the five instrumental ADLs (Lawton IADL Scale). If ADL status cannot be obtained, admission to long-term nursing care (national registries) will be used as a proxy for disability.

Incident dementia: registry/clinical diagnosis (ICD-10 F00-F03, G30, or equivalent codes in national registries). Exploratory supplement: MoCA assessed at 24/36 months; dementia defined as MoCA z-score ≤ -2.0 (age/education-adjusted).

Intervention costs (resistance training and control), prescription medication, and health and care service utilisation during the 12-month intervention period. Costs for the training intervention include fitness centre membership fees and instructor labour costs (time worked + overheads). We will not consider potential travel costs for participants. We will obtain expenses related to prescription medication and health care service utilisation by linking participant data with data from the Norwegian Prescribed Drug Registry, the Norwegian Patient Registry (specialist health services), and the Municipal Patient and User Register (primary care, care services, physiotherapist, and chiropractor). We focus only on implementation costs, thus disregarding research protocol costs (e.g. recruitment).

We use the 12-item short-form health survey (SF-12) to assess health-related quality of life across eight areas, with scores summed into a physical component summary score and a mental component summary score, ranging from 0 to 100, with higher scores indicating a better quality of life.32 Next, we'll convert the SF-12 scores into SF-6D utility scores using the equation by Brazier and Roberts (2004).33 The utility scores range from 0 (equivalent to death) to 1 (equivalent to perfect health). Finally, we'll calculate QALYs for the 12-month intervention period by linearly interpolating SF-6D utility scores for baseline, six, and 12 months

Echocardiographic indices of atrial and ventricular structure and function

During the study unreported mortality will be assessed twice per year by linkage to the Norwegian population registry with the use of a unique 11-digit Norwegian national identification number for each participant.

Montreal Cognitive Assessment Tool

Using the Protein Screener 55+

We will analyse the cost-effectiveness by estimating the Incremental Cost-Effectiveness Ratio (ICER) between the resistance training and control groups. We consider resistance training cost-effective if the ICER falls below the willingness-to-pay threshold (WTP).