The yield curve is not static and may experience parallel or non-parallel shifts. When an economy is overheating and inflationary expectations are rising the rates at the short end tend to rise further than rates at the long end. Central bank open market operations are more effective at the short end of the yield curve than the long end. When an economy is slowing or moving into recession central banks tend to cut rates at the short end aggressively. These shifts provide opportunities to bet on the spread between short-term and long-term rates widening or narrowing.