Collective single-beam effects, driven by impedances and wake fields in the vacuum chamber of high-energy muon colliders HEMC, are evaluated: (i) using techniques that have been applied to proton-proton colliders such as the LHC and extrapolations from it, (ii) using a new technique more applicable to nearly-isochronous HEMC, adding longitudinal and transverse kicks from longitudinal and transverse loss factors. Results from both techniques are presented for HEMC at 10 and 100 TeV center-of-mass energies. ©2000 American Institute of Physics.