To test the hypotheses that 1) 14-days of immobilization of young healthy subjects using a 6 degrees -"head-down-tilt-bed-rest"-model (6 degrees -HDT) would reduce cartilage thickness in the knee and serum Cartilage oligometric matrix protein (COMP) concentration and 2) isolated whole body vibration training would counteract the bed rest effects.
The study was performed and designed in compliance with the Declaration of Helsinki and is registered as trial DRKS00000140 in the German Clinical Trial Register (register.germanctr.de). Eight male healthy subjects (78.0+/-9.5kg; 179+/-0.96cm, 26+/-5 years) performed 14 days of 6 degrees -HDT. The study was designed as a cross-over-design with two study phases: a training and a control intervention. During the training intervention, subjects underwent 2x5-min whole body vibration training/day (Frequency: 20Hz; amplitude: 2-4mm). Magnetic resonance (MR) images (slice thickness: 2mm; in-plane resolution: 0.35x0.35mm; pixels: 448x512) were taken before and after the 6 degrees -HDT periods. Average cartilage thicknesses were calculated for the load bearing regions on the medial and lateral articulating surfaces in the femur and tibia.
While the control intervention resulted in an overall loss in average cartilage thickness of -8% (pre: 3.08mm+/-0.6mm post: 2.82mm+/-0.6mm) in the weight-bearing regions of the tibia, average cartilage thickness increased by 21.9% (pre: 2.66mm+/-0.45mm post: 3.24mm+/-0.63mm) with the vibration intervention. No significant differences were found in the weight-bearing regions of the femur. During both interventions, reduced serum COMP concentrations were observed (control intervention: -13.6+/-8.4%; vibration intervention: -9.9+/-3.3%).
The results of this study suggest that articular cartilage thickness is sensitive to unloading and that vibration training may be a potent countermeasure against these effects. The sensitivity of cartilage to physical training is of high relevance for training methods in space flight, elite and sport and rehabilitation after illness or injury.