This is really a tough question to answer; when someone asks what is the fitness level required for Everest Base Camp Trek ?
Being a frequent traveler/trekker to Everest zone; I can say with confidence that any fitness level is absolutely fine to complete the Everest Base Camp Trek. What is mainly required is your passion level to go there. I believe if you are a nature lover and one who really wants to go there; then you will be there in any fitness level. I have seen many older people in their 70s and 80s trek to Everest Base Camp. I saw many really fit people crawled there but really overweight people successfully completing the trek.
Yes you need a basic fitness level for Everest Base Camp Trek, but you do not need a pro level athlete’s fitness.
Some parts of the trek are really strenuous. Such as Monjo to Namche Bazaar; this part of the trek is really strenuous so walk slow and find your right pace.
Then between Pungi Thanga to Tengboche; this is the last hike before Tengboche and this is a strenuous hiking.
After that, Old Ama Dablam Base Camp; if you are going here on your rest day at Dingboche. I will say this is the strenuous hiking which is equivalent to Kalapatthar. You must go here because from here you can see Mount Makalu and Cho Oyo.
Then Hiking to Lobuche Pass, this part of hike is also strenuous. This starts when you start from a place called Dughla, In between Lobuche to Gorakshep, you need to hike a small pass which is little strenuous. Then the Kalapatthar hike; this is the toughest hike for many people but if you go slow and in your own pace then this will be the most beautiful moment of your life.
If you are doing all the passes like Chola pass, Renjhola pass, Gokyo Ri hiking and Kongma La pass then you will encounter so many strenuous hiking.
So what kind of fitness level is requiring for Everest Base Camp Trek?
A moderate level fitness is perfect for Everest base camp trek.
If you are regular gym guy or regular runner then you are completely fit for this trek.
if you are not doing any kind of physical activities and want to go for the Everest Base Camp Trek then you need to do at least 4 to 5 kilometer walking daily for about 60 days before your trek starts. The key here is to practice and walk for longer duration on a jogging track on a regular basis.
if you are practicing it on a treadmill then walk on a slight incline level.
As I mentioned above, I saw several fit people who crawled during the Everest Base Camp Trek. They get exhausted because they lost interest in trekking. Once you have lost your interest and start thinking why I am pushing myself to this extent or what is the use of such strenuous hike or is this really required for me etc then you will definitely need a rescue and I am sure the fit people I saw they lost their passion. So be moderately fit and enjoy every moment of your trek and this zone is immensely beautiful. Walk on your own pace, drink enough water and do proper acclimatization then you will successfully complete this extraordinary trek.