ISS047e032018 (04/01/2016) --- NASA astronaut Jeff Williams works to install the Cell Biology Experiment Facility (CBEF) Cell Mechanosensing Humidifier. Cell Mechanosensing is a Japan Aerospace Exploration Agency (JAXA) investigation that identifies gravity sensors in skeletal muscle cells to develop countermeasures to muscle atrophy, a key space health issue. Scientists believe that the lack of mechanical stress from gravity causes tension fluctuations in the plasma membrane of skeletal muscle cells which changes the expression of key proteins and genes, and allows muscles to atrophy.