Strength and power comes to those who use these spells. Strength is not only physical strength but also mental and magical.
When casting these spells, the target of the spell becomes stronger for a short period of time. These spells can not be reversed by magic but will wear off over time. Unlike other spells which wear off over time, the strength of the caster does not determine how long the spell lasts, but more the effect of how strong the target becomes.