shad·ow·box 
/ˈʃædoʊˌbɑ:ks/ verb
shad·ow·box·es; shad·ow·boxed; shad·ow·box·ing /ˈʃædoʊˌbɑ:ks/ verb [no obj] : to box with an imaginary opponent as a form of training
▪ He was shadowboxing to stay in shape.
▪ He was shadowboxing to stay in shape.
— shadowboxing noun [noncount]
