This will help minimize the unpleasant or even dangerous effects of altitude, which commonly include headache, fatigue, and nausea. (travelandleisure.com)
If your Peru trip starts in either Lima or Cuzco and you would rather limit the ill effects of altitude sickness, instead of spending time in Cuzco first and then visiting Machu Picchu, head straight to Machu Picchu, spend a night here, another night in the Sacred Valley and then end in Cuzco for a few nights. (onthegotours.com)
Only due to the high passes you travel over on the bus trip in you may feel effects of altitude until arriving to the valley of Chivay. (sastravelperu.com)