The aim of this research is to analyze whether nutritional intervention combined with a multicomponent physical training program based on strength, balance, and aerobic exercises can prevent disability caused during hospitalization in individuals aged 75 years or older admitted for medical conditions, thereby improving functional and cognitive capacity.

To achieve this objective, we will conduct a randomized clinical trial in which patients are randomly assigned to either the control group, which does not perform the physical training, or the intervention group, which participates in the multicomponent physical training program.

The main objective of the present study is to evaluate the differences in the impact of an intervention based solely on physical exercise on the functionality of hospitalized older patients, in an Acute Geriatric Unit, who are malnourished or at risk of malnutrition.

As secondary objectives:

1. To assess and compare changes in body composition following the intervention during hospitalization.
2. To evaluate and compare dietary intake, appetite progression, and food consumption throughout the intervention period.
3. To compare in-hospital infectious complications between the two groups.
4. To describe and compare changes in nutritional biochemical parameters between groups after the intervention and 30 days post-discharge.
5. To study changes in other physical function measures throughout the study period and compare them.
6. To describe the presence of molecular markers related to senescence and sarcopenia in patients and compare them between groups at discharge.
7. To study and compare changes in participants' cognitive status.
8. To evaluate and compare changes in perceived quality of life.
9. To assess and compare changes in maximal dynamic strength before and after the intervention.
10. To describe and compare hospital stays and 30-day readmission rates of study participants.
11. To describe participants' personal satisfaction with the intervention.
12. To describe the presence of potential side effects attributed to the intervention during the study period.

Inclusion Criteria:

• Aged 75 years or above
• Hospitalized in the Acute Unit of the Geriatrics Service at the University Hospital of Navarra
• 4 days or more of expected hospitalization
• Malnourished according to the GLIM criteria or at risk of malnourishment (MUST scale)
• Barthel Index ≥ 60 points
• Capable of tolerating oral intake
• Able to walk (with or without assistance)
• Able to understand instructions and communicate
• Consent to participate in the study after being informed of its objectives and who sign the informed consent (the participant or their legal guardian in case of disability).

Exclusion Criteria:

• Advanced major neurocognitive disorder (GDS 6 and 7)
• Uncontrolled cardiac arrhythmia, acute pulmonary thromboembolism, acute myocardial infarction, or bone fractures within the last 3 months
• Chronic kidney disease stage 4 or 5
• Safe and effective swallowing only with pudding texture
• Inability to participate in the physical exercise program due to physical limitations
• Participate in another study that may interfere with data interpretation or have participated in another study in six months prior to their entry into the study.