Doc talk:Walk Cycle
Motion Capture - Another tool available for creating motion is biovision or motion capture data rendered as images. BVH files are created by recording 3d spatial data of each joint as a person/figure moves (walking, dancing, fighting, etc.) BVH files are used to animate 3d models, but you can view BVH data rendered on 'stick figures' without a 3d program. There are several free BVH viewers available.
Googling for BVH data will lead to many sites that either provide free BVH data, or provide sample BVH data from commerical packages. Viewing the BVH data with mocapsim will provide insight for creating motiong within synfig. Mocapsim can export images of the the BVH motion - so you can also import those to use as a template.
Mocapsim - http://sourceforge.net/mocapsim or search for 'bvh' on sourceforge and you will find a few different bvh players.
If you want to see motion applied to 3d models try daz3d.com for an easy to use windows program. Or, Blender.org for more power (and more to learn.)