Keif Vigor

The target gains a +2 enhancement bonus to its Strength. Once per round as a free action, the target can choose to increase the enhancement bonus by 2 for 1 round; if it does so, it takes 1d6 points of nonlethal damage and the spell's duration decreases by 1 additional round. For every 5 caster levels you have, the target can choose to increase the enhancement bonus by an additional 2, taking an additional 1d6 points of nonlethal damage and decreasing the duration by 1 additional round per increase to the Strength bonus, to a maximum enhancement bonus of +10 and 4d6 points of nonlethal damage at caster level 15th. The subject can't spend more rounds than remain in the duration. When the spell ends, the subject becomes fatigued.