Ion tail formation by neutral beam (D0) injection and second harmonic ion (D+) cyclotron heating in a 50:50 D-T plasma is investigated on the basis of a local Fokker-Planck calculation. The deformation of the deuteron velocity distribution function is examined analytically and numerically. The effectiveness of the tail formation is estimated from the enhancement of the D-T fusion reactivity, (f is the deuteron distribution and G is the 'ov-function', averaged over the isotropic triton distribution). The profile of the integrand typically exhibits two humps in velocity space. This results in a large reactivity enhancement for high energy beam injection. For a radiofrequency (RF) induced tail, a 'wing' or smeared tail rather than a hump is formed. ICRF waves couple well with the beam induced tail ions and enhance the reactivity, especially when the beam is injected perpendicularly to the magnetic field. The efficient use of the power supplied by beam and RF waves to enhance the reactivity is also discussed.