If I remember physics class centrifugal force is exactly matched by cetripetal force in a stable rotating system. The equation for centripetal force required to maintain a circle is m*v**2/r. Seems to me when you are swinging you have a large radius system (arms) which gets the mass moving, then when the wrist downcocks you have this speed loaded into a smaller circle (wrist), which means v (velocity) will increase (r is smaller, and angular momentum is conserved).