Double-blind randomized placebo-controlled clinical trial with two parallel arms. The main objective is to evaluate the efficacy and safety of creatine supplementation in older adults who have been operated on for total knee arthroplasty and undergoing a usual rehabilitation program. The intervention will consist of daily creatine monohydrate supplementation for 12 weeks. The intervention will start after surgery with a loading dose of 20g/day for 1 week and then continue with a maintenance dose of 5g/day for 11 weeks.

Main outcome mesures included muscle mass, muscle strenght, sarcopenia, frailty, functional capacity and physical performance and will be assessed at baseline, 3 and 6 months follow-up.

Inclusion Criteria:

• Persons 65 years of age or older who have been operated on for the first time for total knee arthroplasty,
• who are undergoing an outpatient rehabilitation program according to standard clinical practice,
• who sign the informed consent form.

Exclusion Criteria:

• Chronic renal disease at stage G3b or higher or glomerular filtration rate <30 ml/min/1.73m2.
• Hepatic insufficiency, cirrhosis.
• Neuromuscular and neurodegenerative diseases (amyotrophic lateral sclerosis, multiple sclerosis, muscular dystrophy, myasthenia gravis, Parkinson's disease, etc.).
• Severe or very severe chronic obstructive pulmonary disease (COPD) (GOLD III-IV).
• Moderate or severe chronic heart failure (NYHA 3-4).
• Central sensitivity syndrome (fibromyalgia and chronic fatigue syndrome).
• Moderate or severe cognitive impairment (GDS≥4).
• Moderate-severe dependence for basic activities of daily living (preintervention Barthel index <60 points).
• Hemiparesis, amputation or malformation of any limb.
• Consumption of creatine monohydrate supplements in the last 6 months.