My cameraman, Leon McCarron, and I have now spent more than five months walking south from Mongolia towards Hong Kong.
Before setting off, I wrote in this column about how I had prepared physically for the journey (through training hikes, and learning the best stretching exercises). All this preparation certainly helped. But now, more than 3,000 kilometres later, how have our bodies coped with the day-in, day-out pounding which we have been giving them?
First, it should be explained what kind of strain our bodies are under. On average, we walk for 12 hours a day (covering about 35 to 40 kilometres) for five days, and then take one day off. Our packs weigh around 25kg (primarily from our camping gear, camera gear, clothes and food). Combined with my body weight, this means my feet are taking a 100kg pounding with each step, and as our total distance will eventually be 5,000 kilometres (or five million metres), this means that each foot gets five million 100kg poundings against the road.
So it is testimony to the resilience of the human body (and perhaps the Ecco boots I am using) that our feet are still intact. But at the same time, they have had more problems than the rest of our bodies.
About a month into the expedition, just as we reached the end of the Gobi Desert, I developed a very sore second metatarsal. (The metatarsals are the bones in the feet.) I could barely put any weight on the centre of my foot for several weeks, and had to walk with a limp, taking as much pressure as I could on my hiking poles.
After some extra days off, and inverting my ankle support so it covered my foot, I found the injury was stabilised, and I could start to walk at full speed again, and both Leon and I continued uninjured for a while.
The next injury, two months into the expedition (while we were walking down the frozen Yellow River valley), was Leon's back. This started to give him great pain, which we thought was due to his rucksack becoming unbalanced.
We fell behind schedule after setting definite deadlines for our return home: my long-suffering wife is waiting for me, we have a television production schedule, and Leon needs to be back in Northern Ireland to be an Olympic torch-bearer. This meant that we could not afford more time off for resting, so Leon soldiered on with the help of ibuprofen and stretching, and, thankfully, his back, like my foot, gradually stabilised.
At about the same time, I started to get my first proper blisters of the expedition, and each evening before bed, I had to use my pen knife and cut open the various bubbles which were forming on my feet, and then douse everything in iodine to prevent infection (which, you can imagine, led to a particularly intense kind of pain).
My blisters recovered but in the fourth month, Leon began to get terrible blisters, some of which started to cover his whole foot, and he had to take antibiotics to stem the infections. I cannot say why it is that our feet managed for more than two months before the blisters started, as I'd have thought they would toughen up, but it seems that sometimes these things just suddenly happen, and once you have one blister, it slightly alters the way you walk, and this in turn provokes more.
And now in our fifth month, Leon has suddenly developed an extremely itchy sweat rash on his back. It is getting hot now, so we need to start jumping into more streams to wash our bodies and clothes. Meanwhile, my feet often feel bruised and battered in the last hours of the walk each day, although it is amazing how these annoyances seem to clear up by the following morning.
Beneath all these niggling injuries, there is an incredible, deep-seated, exhaustion seeping through us. It is not only physical exhaustion, but also mental - from having to maintain our concentration as we walk - whether to avoid twisting our ankles on tiny, mountain or forest paths, or avoid being hit by a truck on busy roads.
Our days off are mostly filled with administrative and research tasks, with little time for our minds to rest.
But despite the aches and pains, I think we've done pretty well, considering how much we've put our bodies through. The incredible, constantly changing landscape we pass through and the amazing, fun people we encounter are enough to make me stop wishing for the walk to end, and instead appreciate every one of those five million steps to get home to Hong Kong.
There will be plenty of time for my body to rest after that.
Rob Lilwall's previous expedition, Cycling Home From Siberia, became the subject of an acclaimed motivational talk, a book, and a National Geographic TV series. Every week in Health Post, he will write about the progress of his new expedition, Walking Home From Mongolia, which is in support of the children's charity Viva. walkinghomefrommongolia.com