Fortunately, there is no real need to worry about altitude here. The highest point of the TMB is a little over eight thousand feet, so elevation is not going to be much of a factor.
What will be a factor are the miles. There’s a lot of them. And the up and down. And VERY steep trails. To get ready, walk as much as possible with weight on your back, and do as much walking as possible uphill AND downhill on the steepest trails you can find. Obviously, it helps to be able to train in the mountains, and these do NOT necessarily have to be high mountains. The TMB after all is NOT a high elevation mountaineering route, it is a walking tour of high alpine valleys that crosses some comparatively moderate (by Alpine standards) passes. The height of these passes is equivalent to a major Appalachian summit.
And that’s exactly how we prepared, by hiking in the Appalachians. In fact, we prepared by doing sections of the Appalachian Trail and surrounding trails. The summit of Standing Indian Mountain in North Carolina is actually higher than the Col de Voza, for example. So, don’t fret if you don’t have big mountains at hand, even hills will do.
But you must do a LOT of walking. Our advice is to build up slowly, or else you will encounter the devil’s paradox of athletic training…you must train to avoid injury and burnout, but the harder you train, the more likely you are to injure yourself or burn out. The risk of this can be reduced significantly if you begin within your limits and build up slowly.