When using extra effort (see Extra Effort in The Basics), you can gain two of the listed benefits, even stacking two of the same type of benefit. However, you also double the cost of the effort; you’re exhausted starting the turn after your extraordinary effort. If you are already fatigued, you are incapacitated. If you are already exhausted, you cannot use extraordinary effort. Spending a Victory point at the start of your next turn reduces the cost of your extraordinary effort to merely fatigued, the same as a regular extra effort.
D20 Hero SRD Advantages Article- http://www.d20herosrd.com/5-advantages