Site: nominal (<4% loss)
Site: watch (4–10% loss)
Site: elevated (>10% loss)
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Microgravity bone loss is not one number — it is five or six different rates happening at once, one per skeletal site, each responding to a different mix of exercise devices. This 3D simulator places bone-density markers at the femoral neck, lumbar spine, tibia, calcaneus and forearm on a floating astronaut figure, and shrinks and recolors each marker independently as its own site-specific loss accumulates over a simulated mission — driven by exactly which combination of ARED resistance training, treadmill running and cycle ergometer work the crew actually performs each day. Toggle devices on and off to see why the real ISS exercise protocol pairs a resistance device with an impact-bearing cardio device rather than relying on either alone.