Being fit is no guarantee for getting to the summit of Kilimanjaro. However fit you are you can still be affected by the altitude, though obviously there are a number of ways to minimize the effects. Even then, it remains true that people in their 80s have successfully summited while extraordinarily fit athletes have failed to summit.
But one thing that is for sure is that the fitter and stronger you are, the more you will enjoy the experience.
Cardio training and strong muscles will help you with the daily hiking on the mountain of between 5 and 7 hours. If you can, get out and hike at home whenever possible in the weeks and months leading up to your Kilimanjaro climb. Fill up and strap on your day bag to get used to carrying extra weight, and be sure to wear in your hiking boots too. Hike steep inclines and downhills, do steps and strengthen leg muscles. Being a runner or cyclist helps, but it does not fully prepare you for a tough 6-day hike.
Lots of stretching to improve your flexibility before setting off will also help muscles from becoming too stiff when on the mountain. It’s also a good idea to stretch at the beginning and end of the day whilst on the mountain.
But for all the work you might put in beforehand, the best advice for physical success is to take it slow when climbing the mountain, however fit you are or aren’t. “Pole pole”, slowly slowly, as they say in Tanzania. This will be your mantra on Kili. Your body needs to adapt to the thin air and lack of oxygen at altitude.
Almost everyone will experience at least some symptoms of altitude sickness at some point. Headaches, nausea and lack of appetite are all part of the game, but can be alleviated with rest, nutritious food and water. Obviously prior training at altitude will help in this regard, but it’s still no substitute for walking slowly and rhythmically whilst on the mountain.
Having said all of this, anyone who has successfully summited Kilimanjaro will tell you that mental strength is more important than physical strength fitness. Stay positive at all times, don’t panic or get despondent, follow the instructions of your guides at all times. All of this is key. You can do it.
Also note that the minimum age for joining a Kili trek is 12 years (with conditions) because children are more susceptible to altitude sickness than adults.