Proof test	100% maximum rating of the test machine.  It is the maximum rating because there is no shock load to the machine.
Break test	75% of the proof (maximum) test load.  The reason this is decreased to 75% is because there is a shock load to the machine, load cell & hydraulic system.  Therefore, it is down rated to 75% of the proof load.
Cycle test	50% of the proof (maximum) test load.  A machine that is used for cycle loads will fatigue a lot faster than a machine that is used for proof loading or break testing.  The reason being is the cycle loading puts more cycles onto the machine.  Therefore, everything fatigues at a much faster rate.  Because it fatigues at a much faster rate the maximum load rating is at 50% of the proof test load.