How to limit the rotation of knees, feet, ankles and similar joints? Is there any trick to prevent bending of the knees, ankles and alike so they stop at a certain rotation point, let say 45 degree angle?
I have a character that I'd like the joints to stop rotating "naturally" so it doesn't look weird. The same goes for the knees, feet, ankles, arms, etc ...

See ref imgs and attached .blend file:


.blend file is 37MB and maximum limit is 30MB on blend-exchange.giantcowfilms.com so here's the link: http://we.tl/TFb1T7WNoV

No python scripts please. I'm a total noob.
Edit:
In looked back at this old answer and realized you were using an IK rig. To limit this, there is an inverse kinematics section to the bone properties.

Select the bone you want to constrain, and make sure you are in posed mode. There should be a bone constraints window:



By check boxing 'limit' you can set a bone to only bend so far in IK mode.

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  Old Answer




You can add a "limit Rotation" constraint, as you can see set up there. 
It also has other bone limitations; go ahead and mess around with it.