Effects of 60-day-6° Head-down Bed Rest on Cartilage and Function of the Knee Joint

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.