He 's using a lot of muscle force like this , or contractile force .
A real simple example is if you 're in a fight , you encounter somebody 's arms like this , and he 's firing his biceps .
somebody 's using a lot of muscle force like this , or contractile force .
A real simple example is if you 're in a fight , you encounter somebody 's arms like this , and he 's firing his biceps .