Interest rate movements are based on the outlook for the economy and the risk a bond holder is willing to take when compared to other investments. Mortgage interest rates are based on the market of Mortgage Backed Securities.
If bond yields are more attractive than other investments, the price of a bond will increase and rates (yield) decreases. This can happen when investors are looking for more secure investments than the stock market. When the economy is expanding there is a higher demand for credit, so rates move higher; whereas when the economy is slowing, the demand for credit decreases and so do interest rates.