Doing less exercise could deactivate a vital protein in the body, causing further inactivity and making exercise more difficult, new research suggests.  Deactivating the Piezo1 protein, a blood flow sensor, reduces the density of capillaries carrying blood to the muscles.  This restricted blood flow means activity becomes more difficult and can lead to a reduction in how much exercise is possible. This helps to explain the biology of why exercise becomes harder the less you do.