You can find an action clip's best cycle and then trim the clip's other cycles to match that one or set markers to show where the best cycle is. Depending on what kind of animation you have, there are two different algorithms used for the cycles: energy (rotations) or frequency (marked parameters).
To find cycles using the rotations of IK joints
Move to a frame to define the starting point for finding cycles.
Choose Clip 
Find Cycles from the mixer's command bar.
In the Find Cycles dialog box, the Energy algorithm is selected. If it finds a period, the trim or mark operation will be performed for that period.
Enter a minimum cycle Duration in frames. All cycles found with a duration of fewer frames than this are rejected.
Select Trim Clip or Add Markers to do either of these operations.
Trimming tries to keep as many periods as it can. If you add markers, you can also specify a generic Marker Name. Markers are added at the initial time and then at regular intervals separated by the period found.
To find cycles on marked parameters
Choose Clip Find Cycles from the mixer's command bar.
The Frequency algorithm is selected in the Find Cycles dialog box. If it finds more than one period is found, the trim or mark operation will not be performed because multiple cycles cannot be calculated.
Enter a minimum cycle Duration in frames. All cycles found with a duration of fewer frames than this are rejected.
Select Trim Clip or Add Markers to do either of these operations.
Trimming tries to keep as many periods as it can. If you add markers, you can also specify a generic Marker Name. Markers are added at the initial time and then at regular intervals separated by the period found.
