Objective: To investigate the effects of long-term simulated unloading in bed on articular cartilage quality based on functional magnetic resonance imaging (FMRI) and Knee joint function.

A total of 26 subjects were recruited for a 60-day period of head-down bed rest (HDBR). The bed rest position is a 6° downward tilt of the head, and all daily activities are performed in this position. We will perform functional MRI scans of the right knee joint using T2 mapping sequences to assess tissue composition and water content before and after HDBR. Functional assessments, including the Y-Balance Test and International Knee Documentation Committee (IKDC) scores, were performed pre-HDBR and post-HDBR.We will divide each participant's knee cartilage into 18 regions and measured T2 values according to the whole organ magnetic resonance imaging score (WORMS) partitioning method.

Inclusion Criteria:

• (1) male; (2) age 25-50 years old; (3) height between 160-175 cm, weight ≥50kg, and BMI between 18.5-26 kg/m²; (4) good general health status.

Exclusion Criteria:

• (1) history of alcoholism; (2) smoking ≥5 cigarettes/day in the 3 months before the test; (3) drug dependence or use of medications affecting bone metabolism within 2 weeks before screening; (4) presence of metal implants, severe vertigo, or severe snoring.