Neutral-beam energies of 200 to 500-keV D0 may be required to ensure adequate penetration into the centre of ignition-sized tokamak plasmas. However, the beam energy requirement can be reduced by using a start-up scenario in which the final plasma is formed by major-radius compression of a beam-heated plasma whose density-radius product, na, is determined by satisfactory neutral-beam penetration. "Compression boosting" is attractive only for plasmas in which nτE increases with na, because a major-radius compression C increases na by C3/2. This paper analyses the dependence on C of beam energy and beam power for plasmas which obey "empirical scaling laws" of the type nτE∝(na)2. The dependences on C of stored magnetic energy and TF-coil power dissipation are also determined. It is found that a compression ratio of 1.5 to attain the ignited plasma permits adequate penetration by ·150-keV D0 beams.