The problems of reactivity enhancement and fractional energy deposition associated with the slowing down of energetic fusion ion products in a burning plasma are investigated. The distribution functions of fuel ions and energetic products are obtained from a self-consistent set of Fokker-Planck equations. Using a perturbation method, a numerical iteration procedure has been worked out for D-T, D-3He. D-D and catalyzed D-D fusion cycles. For all cases, the enhancement in the fusion reactivity is found to be negligibly small. The fractional energy deposition from fusion products into ions and electrons is accurately predicted by an analytical formula derived for a Maxwellian plasma. Also, a global power balance model gives an excellent estimate of the mean fuel ion temperature.