SAS Travel advises that you only do the 4-day Inca Trail hike if you’re physically fit. I thought I was in pretty good shape and ready for the trip, and I near puked every day. Now I’ll define what I called physically fit, because I obviously wasn’t. For 2 months I walked 6 flights of stairs up to my office at least twice a day, and played squash, ball hockey, ice hockey and ran track each at least once a week. I was fine for the first day, finishing first or second place in the group, and by the 4th day I was dead last, wearing a knee brace on loan from an ex-rugby player in the group and 2 borrowed walking sticks from a couple girls.
Keep in mind you pass altitudes of 4,000 meters and if you’ve never been at such an altitude you don’t know how your body will react. I was light headed, short of breath, my joints (fingers especially) swelled up, and my knees buckled big time. Your body is likely not used to those altitudes, so if you’re not in shape don’t bother, seriously.
It’s recommended that when you get to Cuzco you should stick around and acclimatize to the altitude for a couple days, I say more like 4 days. And Cuzco is a VERY cool place to hang out in for 4 days.
You may hear of people dying on the Machu Picchu tour (falling off the side of a mountain or collapsing from exhaustion on the Inca Trail). This is true, and you can die, if you’re an idiot. For example, there are places along the Inca Trail hike that you are not advised to venture out to, or climb up a mountain side you’re not advised to climb. Some people wanted to be “that guy” and paid the price. If an idiotic adrenaline rush doesn’t kill you, you’ll likely end up breaking a leg, arm, back or with a nasty concussion.