Orphan receptor that acts as a transcription activator in the absence of bound ligand. Binds specifically to an estrogen response element and activates reporter genes controlled by estrogen response elements (By similarity). Induces the expression of PERM1 in the skeletal muscle. {ECO:0000250, ECO:0000269|PubMed:11864604, ECO:0000269|PubMed:18063693, ECO:0000269|PubMed:19067653, ECO:0000269|PubMed:23836911}. This is the function of ESRRG (estrogen related receptor gamma, ENSG00000196482).