I have heard that when we lie, our body becomes physically weaker.

Because of this phenomenom you can tell if someone is lying by having them spread out their arms perpendicular to their body. Then you can apply pressure downward, while they resist the pressure in the opposite direction.

It is thought that when the person lies, they will be significantly weaker than when they are telling the truth.

Is this true? Thoughts?

Not true.

I heardsomething similar to that, but about heavy metal music. I was told that listening to "negative" music can make you weak. It was "proved" in a similar fashion. I don't think it is true however.