Doubles isn't too tiring, even at the professional level. The rallies are typically short. Myskina is relatively fit, used to playing singles on consecutive days even to win other tournies. She needs to watch out about taking the doubles so seriously that she gets mentally drained by the end. Otherwise, it's okay.
As far as I recall the only minor danger of doubles is getting something strained. Otherwise, only Hingis complained repeatedly of being too tired afterwards to win her singles match the next day. Remember that fatigue was a factor for her regardless of whether she was playing doubles in the tournament. She was just always tired during those 3rd sets (except when playing Monica).
Someone is quietly turning back the clock...to them bulldozer dayz...
Always on the lookout for a great tennis match.