Tired = Wrong

Do your arms start to feel tired during pushing hands? Do your arms suffer from muscle aches after pushing hands? If so, you are doing it wrong. It means that you are using the muscle strength of your arms, rather than the force generated by your legs. It means that you do not know how to relax, that you are unable to relax your kua, unable to relax your arms.

So while you may think that you are not using muscle strength, while you may think that you are relaxing your arms and kua, if your arms start to feel tired during pushing hands, it means you are not. It is one of the easiest gauge of whether you are using brute force, or following the principles of taiji.