I'm terrified.

I'm on a plane constantly checking my oxygen saturation levels on the back of the Galaxy Note 7, seeing how the lower pressure of the plane is affecting my blood.

You see, I did something stupid. I signed up for a race in Colorado - the Pike's Peak Ascent - that would see me running up the side of a mountain.

I watched a video. It looked OK. It looked like running up a hill for a bit longer than usual, and the distance was 'only' a half marathon - not easy, but not an alien length.

That was back at Christmas. I didn't think much more of it (other than sitting on my laptop in the middle of an English countryside in the middle of February, desperately refreshing the site while tethered to my phone's data to connection to make sure I got into the race) for a few months after that.

Then, in July, I was watching a program about mountain climbing and the ill-effects of altitude sickness. I idly wondered 'Hmmm, I'm going up a mountain. Should I be worried about this?'

Should I be worried about this?

Actually, let's rewind quickly and explain why I'm doing the race. About a year ago I became obsessed with a running analytics platform called Smashrun. It sucks in all your running data from the apps, sensors or wearables you've strapped on over the years to give a variety of insights into your improvements (or lack thereof).

But one of the most-adored things by any runner is the achievement of a medal, and Smashrun offers 113 different challenges to hit. They range from running a mile to hitting a sub 2:55 marathon - and I decided that I was going to try and do them all in one year for charity.

Hence me doing this race: one of the badges is 'logging a run with an ascent greater than 2652 meters', the rise of Pike's Peak. And there was a race up that mountain: how convenient.

It's a long way up...

I thought 'Well, that's just running. I like running. And it's up a hill. I've done hills before. I'll just walk if I have to.' And that was the last of it, until the documentary made me check out what I was up against.

I'm suddenly spending hours poring through YouTube and reading race reports online to work out what I was up against, dipping into forums on the commute to work and sneaking headphones in my pocket to watch another video in an idle minute.

It sounded horrendous. 11% incline and apparently my research told me 2600 meters is altitude sickness territory, and the worry really grew.

Then the really, really horrible smackdown came - I'd forgotten about sea level. You see, Colorado Springs (obviously) isn't on the shoreline... It's about 1400 meters above it. So combine the two together and I'll be cruising over 4000 meters at the end, possibly passing out or pooping my pants before the finish.

New pants please

I started running up and down hills like a madman, three-and-a-bit weeks out from the race. I strapped on the Garmin Forerunner 920XT (which has a barometric altimeter inside to register ascent through changes in air pressure) to work out how much distance I was covering by heading through these gradients. It wasn't a lot.

I headed to the gym a couple of times, boosting the incline up on the treadmill between 9-13% and spending a few hours at a time just cruising as slowly as possible to see if I could actually do this, and not coming to any conclusions.

Then, last week, I found out about an altitude room at the Virgin Active gym in London - if I could get down there and do some running to simulate the top of the mountain, that'd be great thing to help settle my nerves, right?

Apart from feeling thoroughly out of place in the superbly plush surroundings of the high-end gym (I was wearing a t-shirt with a reindeer sporting sunglasses), I had my oxygen saturation levels monitored to check I wasn't a health risk (99%, woo!) and we headed into the chamber.

Inside the chamber.

As I entered the glass room I was surprised to find out that it didn't really feel that different. We were theoretically standing at 3000 meters above sea level, but I felt OK.

The room packs bikes and treadmills, and our trainer Lucy ran through some basics to induct us to using the equipment at the higher altitude. This is the same thing used by footballers, world-class triathletes and other generally fit types, so I felt more confident, especially as I pushed the treadmill incline up and began to run hard.

I was feeling OK. I might be able to do this!

But then I spoke to Lucy, and realized that things might not be that simple: "The basic benefits of altitude training are that you're going to achieve more in less amount to time. Your body is stressed, heart and lungs are stressed more and you're going to have to adapt to that, which means you're going to get fitter faster," she told me.

When pressed about how it would affect my training for Pike's Peak Ascent, she was confident it would help:

"The main benefit [of training at altitude] is fitness, as you're going to get more used to running harder, going to go into oxygen debt and go anaerobic, which means you're running out of oxygen faster."

What are my chances?

Yeah, that's cool (I love feeling sick when running)... But what about helping me deal with the altitude sickness? Would this 20 minute induction help at all?

"To train at altitude, and in terms of dealing with altitude sickness, you won't get that in here. Unless you literally stayed in here all day and slept here, you're not going to get blood profile changes [where spending days at high altitude forces your body to increase red blood cells to carry oxygen more efficiently].

"This training will help you get fitter, so you'll suffer less with feeling tired, got that mental bank to come back on. In terms of reducing altitude sickness, spend time at altitude before you do your race, to acclimatize and get changes in blood profile."

Ah, crap.

Ah, crap. I'm also slightly worried when I realize that Virgin Active doesn't increase the altitude simulation above 3000 meters for 'health and safety reasons'.

Again: ah, crap.

So, here I am. On a plane about to descend into the Rockies, to spend up to six hours on my feet trying to trek up a mountain at some sort of pace while constantly panicking about running out of air. For pity's sake, there's a bit where trees don't grow because there's not enough air.

I'm terrified.