This run cycle template can be useful to help you keyframe a running character. I made this one a few years ago after studying how other characters moved and how people run. A run cycle template can be used in any modeling and animation software, but in 3ds Max I generally create a plane object, then apply the run cycle template to the plane, and then I will freeze the plane, but change the visibility of frozen objects to non-gray, so that I can see the template. Then I keyframe my biped or other character using the template as a guide. You will need to click on the image to see the full-size version. Then right-mouse click and choose Save As. This character happens to be carrying a gun, so the arms aren’t moving in a pumping action. Also, this image is faded so it is easy to distinguish from the actual biped or rigged character, but if you need to brighten it up you can do so in Photoshop.
Take special care to make sure that the first frame and the final frame are exactly the same, otherwise your character will “stutter” a bit at the end of each cycle. Depending on the game engine you are using, you may need to slide the position of the template (and the plane it is tied to) so that the character runs in place – or, some game engines insist that your character actually cover the distance.